User Panel
User Panel
User Panel
|
Posted: 4/16/2023 9:48:24 AM EDT
[#1]
The water has always been pretty muddy here... It's hard to determine if the "F" height FSBs came about because of the flat top upper or if they were needed due to the carbine length sight radius. Possibly it's both. Possibly it was Colt just wanting to have a proprietary part with the M4/M4A1 and M16A4? Or possibly it was so the military didn't have to stock two different height front sight posts?
What I do is I just keep a bunch of .040 taller front sight posts on hand just in case I run into a situation where I can't zero without the front sight coming out too high beyond the shelf of the FSB. Of course I still do my best to keep "F" height FSBs matched with flat top uppers and A2 height FSBs matched with fixed carry handle uppers. The only times I've ever needed to use the taller front sight posts has been on flat top uppers with carbine length sight radius and A2 height FSBs with mil-spec height rear sights, but even the need for the taller front sight posts in that scenario is about 50/50. So either tolerance stacking or just the way a particular barrel shoots appears to be a factor here. My source for the .040 taller FSPs. > https://shop.windhamweaponry.com/product/9349056-mod/ |
|
|
|
Posted: 4/16/2023 10:33:51 AM EDT
[#2]
Quote HistoryQuoted: The water has always been pretty muddy here... It's hard to determine if the "F" height FSBs came about because of the flat top upper or if they were needed due to the carbine length sight radius. Possibly it's both. Possibly it was Colt just wanting to have a proprietary part with the M4/M4A1 and M16A4? Or possibly it was so the military didn't have to stock two different height front sight posts? What I do is I just keep a bunch of .040 taller front sight posts on hand just in case I run into a situation where I can't zero without the front sight coming out too high beyond the shelf of the FSB. Of course I still do my best to keep "F" height FSBs matched with flat top uppers and A2 height FSBs matched with fixed carry handle uppers. A while back I bought one of the US Ordnance built Colt GAU 5/A/A, it came with a F Marked front sight post with integrated carry handle and when I got it home from the poorly lit dark gun store and saw that I went like, WTF? There was no F marked sights back then. So I contacted US Ordnance and eventually spoke with the owner who explained it to me, it got thru QC because their main assembler had just died. He stated it should have been ground off and re parked. I'm like so it needs a F height site and he said YES due to the Carbine length site radius. They sent me a Return label, I shipped gun back, they received it on a Friday, replaced barrel on Friday, fixed a couple of other gripes I had, shipped back out on same Friday and it was perfect when I got it back lol. With a F height site but no F. They replaced barrel I know because thats what they told me they would do and the site was canted, what I got back was perfectly straight. That was one of my other gripes they fixed. So he stated as fact what you posted. Owner of US Ordnance Curtis Debord should know if anyone does. |
|
|
|
Posted: 4/16/2023 11:02:38 AM EDT
[#3]
Quote HistoryQuoted: A while back I bought one of the US Ordnance built Colt GAU 5/A/A, it came with a F Marked front sight post and when I got it home from the poorly lit dark gun store and saw that I went like, WTF? There was no F marked sights back then. So I contacted US Ordnance and eventually spoke with the owner who explained it to me, it got thru QC because their main assembler had just died. He stated it should have been ground off and re parked. I'm like so it needs a F height site and he said YES due to the Carbine length site radius. They sent me a Return label, I shipped gun back, they received it on a Friday, replaced barrel on Friday, fixed a couple of other gripes I had, shipped back out on same Friday and it was perfect when I got it back lol. With a F height site but no F. They replaced barrel I know because thats what they told me they would do and the site was canted, what I got back was perfectly straight. That was one of my other gripes they fixed. So he stated as fact what you posted. Owner of US Ordnance Curtis Debord should know if anyone does. Quote HistoryQuoted: Quoted: The water has always been pretty muddy here... It's hard to determine if the "F" height FSBs came about because of the flat top upper or if they were needed due to the carbine length sight radius. Possibly it's both. Possibly it was Colt just wanting to have a proprietary part with the M4/M4A1 and M16A4? Or possibly it was so the military didn't have to stock two different height front sight posts? What I do is I just keep a bunch of .040 taller front sight posts on hand just in case I run into a situation where I can't zero without the front sight coming out too high beyond the shelf of the FSB. Of course I still do my best to keep "F" height FSBs matched with flat top uppers and A2 height FSBs matched with fixed carry handle uppers. A while back I bought one of the US Ordnance built Colt GAU 5/A/A, it came with a F Marked front sight post and when I got it home from the poorly lit dark gun store and saw that I went like, WTF? There was no F marked sights back then. So I contacted US Ordnance and eventually spoke with the owner who explained it to me, it got thru QC because their main assembler had just died. He stated it should have been ground off and re parked. I'm like so it needs a F height site and he said YES due to the Carbine length site radius. They sent me a Return label, I shipped gun back, they received it on a Friday, replaced barrel on Friday, fixed a couple of other gripes I had, shipped back out on same Friday and it was perfect when I got it back lol. With a F height site but no F. They replaced barrel I know because thats what they told me they would do and the site was canted, what I got back was perfectly straight. That was one of my other gripes they fixed. So he stated as fact what you posted. Owner of US Ordnance Curtis Debord should know if anyone does. I'd say that's a pretty good confirmation as to the purpose. Now why they would designate the taller FSBs with an "F" is kind of a mystery? You'd assume that it means for use on "F"lat top uppers. But if it was really for the carbine sight radius then why not designate them with a "C" for carbine? And then you have the commercial manufacturers which send out flat top carbines with A2 FSBs and standard height front sight posts and make up for it with a shorter, non mil-spec height carry handle which seems to solve the issue. |
|
|
|
Posted: 4/16/2023 11:14:10 AM EDT
[#4]
A few things:
It’s not widely known, but the height of an A1 fsb is not the same as on an A2. Folks tend to think of just F or non-F, but the fsb got taller going from A1 to A2, and again going from A2 to F. I believe that the primary motivation for the F-height fsb was the flattop receiver. Some folks will insist otherwise, but the rear sight on a detachable carry handle sits higher than on an A2. I have both side-by-side on my workbench right now, and the difference is indisputable. But the fact that the M4 is a carbine may have contributed as well. The story about carbines needing a higher front sight because of their shorter sight radius does make sense qualitatively, but if you put in some numbers and do the math, it starts to look pretty shaky. Considering the geometry alone, you’d need only about 0.015” of extra height to make up for the sight radius — just two clicks of the sight post. And if you account for the reduced muzzle velocity of the shorter barrel, you’d get back one of those two clicks. Still, Colt seemingly believed that carbines needed a higher front sight. I recently came across a pre-M4 carbine barrel (maybe from a 727 or late 723), and sure enough, it has an extra-high sight post. My working hypothesis is that the difference is due to recoil — the little carbine has more muzzle rise than a rifle, and hence it needs a higher front sight to compensate for that. Really that’s just a guess, but I’m sure that the sight-radius explanation isn’t the whole story. The effect is just too small. |
|
|
|
Posted: 4/16/2023 11:35:47 AM EDT
[#5]
Quote HistoryQuoted: A few things: It’s not widely known, but the height of an A1 fsb is not the same as on an A2. Folks tend to think of just F or non-F, but the fsb got taller going from A1 to A2, and again going from A2 to F. I believe that the primary motivation for the F-height fsb was the flattop receiver. Some folks will insist otherwise, but the rear sight on a detachable carry handle sits higher than on an A2. I have both side-by-side on my workbench right now, and the difference is indisputable. But the fact that the M4 is a carbine may have contributed as well. The story about carbines needing a higher front sight because of their shorter sight radius does make sense qualitatively, but if you put in some numbers and do the math, it starts to look pretty shaky. Considering the geometry alone, you’d need only about 0.015” of extra height to make up for the sight radius — just two clicks of the sight post. And if you account for the reduced muzzle velocity of the shorter barrel, you’d get back one of those two clicks. Still, Colt seemingly believed that carbines needed a higher front sight. I recently came across a pre-M4 carbine barrel (maybe from a 727 or late 723), and sure enough, it has an extra-high sight post. My working hypothesis is that the difference is due to recoil — the little carbine has more muzzle rise than a rifle, and hence it needs a higher front sight to compensate for that. Really that’s just a guess, but I’m sure that the sight-radius explanation isn’t the whole story. The effect is just too small. And surprisingly after being on here for over 20 years I only herd recently that A1 height sights were shorter than A2 height sights. I believe it was lysander that pointed that out, but also Molon with his comparison of the different front sight posts years ago. But not only was the A1 front sight post shorter than the A2 front sight post, the shelf on the A1 FSB and the A1 rear sight was also shorter as lysander cleared up. I know Colt was sending out their 6720s with their taller 9mm front sight posts to make up for the barrels having A2 FSBs. But they weren't super consistent about that as they have also sent them out with standard front sight posts as my brother has a factory complete 6720 that came that way. While I have both a factory 6720 upper and a 6720 barrel assembly that came with the 9mm front sight posts. And only one out of the three actually needed the taller front sight post. Clear as mud. 
|
|
|
|
Posted: 4/16/2023 11:58:38 AM EDT
[#6]
the sight radius thing doesn't make sense. A1 carbines existed for decades with the standard FSB. I don't recall there ever being f-marked FSB until flat top uppers came out
|
|
|
|
Posted: 4/16/2023 12:17:34 PM EDT
[#7]
Quote HistoryQuoted: the sight radius thing doesn't make sense. A1 carbines existed for decades with the standard FSB. I don't recall there ever being f-marked FSB until flat top uppers came out Though we also had a member here (not sure if he posts here anymore) that insisted that all pre-flat top/pre-"F" height FSB Colt carbines came with taller front sight posts to make up for the carbine sight radius. No one could ever verify this though as no one seemed to pay any attention to the height of their front sight posts back in the early days of the AR15. |
|
|
|
Posted: 4/16/2023 3:34:25 PM EDT
[#8]
Quoted: I figured out the height of the fsb on rifle vs carbine is diff due to its distance from the rear sight, not because a2 is diff height rear than a1. Right? Why, then, do carbines with a1 uppers have non-f marked sight? My opinion on all this drama is that it is completely silly: It's only 1/25th of an inch! 1/4th of an inch is 5x that amount! |
|
|
|
Posted: 4/16/2023 3:40:15 PM EDT
[#9]
Quote HistoryQuoted: A few things: It’s not widely known, but the height of an A1 fsb is not the same as on an A2. Folks tend to think of just F or non-F, but the fsb got taller going from A1 to A2, and again going from A2 to F. I believe that the primary motivation for the F-height fsb was the flattop receiver. Some folks will insist otherwise, but the rear sight on a detachable carry handle sits higher than on an A2. I have both side-by-side on my workbench right now, and the difference is indisputable. But the fact that the M4 is a carbine may have contributed as well. The story about carbines needing a higher front sight because of their shorter sight radius does make sense qualitatively, but if you put in some numbers and do the math, it starts to look pretty shaky. Considering the geometry alone, you’d need only about 0.015” of extra height to make up for the sight radius — just two clicks of the sight post. And if you account for the reduced muzzle velocity of the shorter barrel, you’d get back one of those two clicks. Still, Colt seemingly believed that carbines needed a higher front sight. I recently came across a pre-M4 carbine barrel (maybe from a 727 or late 723), and sure enough, it has an extra-high sight post. My working hypothesis is that the difference is due to recoil — the little carbine has more muzzle rise than a rifle, and hence it needs a higher front sight to compensate for that. Really that’s just a guess, but I’m sure that the sight-radius explanation isn’t the whole story. The effect is just too small. Fn fal requires a SHORTER post when u chop barrel from 21" to 17.5" and the theory is that longer barrel elevates the muzzle higher during this recoil that theorietically flips the muzzle back before bullet leaves the barrel. |
|
|
|
Posted: 4/16/2023 3:41:44 PM EDT
[#10]
Quote HistoryQuoted: the sight radius thing doesn't make sense. A1 carbines existed for decades with the standard FSB. I don't recall there ever being f-marked FSB until flat top uppers came out Maybe some of those were taller, just not marked as such |
|
|
|
Posted: 4/16/2023 9:45:15 PM EDT
[#11]
Quote HistoryQuoted: And surprisingly after being on here for over 20 years I only herd recently that A1 height sights were shorter than A2 height sights. I believe it was lysander that pointed that out, but also Molon with his comparison of the different front sight posts years ago. But not only was the A1 front sight post shorter than the A2 front sight post, the shelf on the A1 FSB and the A1 rear sight was also shorter as lysander cleared up. I know Colt was sending out their 6720s with their taller 9mm front sight posts to make up for the barrels having A2 FSBs. But they weren't super consistent about that as they have also sent them out with standard front sight posts as my brother has a factory complete 6720 that came that way. While I have both a factory 6720 upper and a 6720 barrel assembly that came with the 9mm front sight posts. And only one out of the three actually needed the taller front sight post. Clear as mud. If you measure the height above the bore centerline of a A2 upper to the shelf the rear sight base rests on when fully down, it is 1.948" If you measure from the bore centerline to the top of the rail on an M4 the height is 1.218". If you measure the height from the seating plane of the handle rail to the shelf for the rear sight base, the height is 0.833" giving a total distance of 2.051" So, the M4 with a carry handle moves the position of the rear sight up a full 0.103". The F "Front Sight", P/N 12972681, (the correct term for what everyone incorrectly refers to as the FSB) is taller to the sight shelf because the rear sight is taller. |
|
|
|
Posted: 4/16/2023 10:17:36 PM EDT
[#12]
Quote HistoryQuoted: So, the M4 with a carry handle moves the position of the rear sight up a full 0.103". The F "Front Sight", P/N 12972681, (the correct term for what everyone incorrectly refers to as the FSB) is taller to the sight shelf because the rear sight is taller. Measuring the examples I have on hand, the A2 windage screw is only about 0.050” lower (relative to the bottom of the receiver) than with a carry handle and flattop receiver. The difference between the sight bases is visible by eye. One point I’m not clear on is how the aperture heights above the windage screw compare on A1 vs A2. The height of the windage screw seems to be the same, and yet the A2 uses an FSB that’s ~0.032 higher than the A1. Any thoughts? |
|
|
|
Posted: 4/16/2023 10:42:37 PM EDT
[#13]
Poking around the TDPs, the M4/M4A1/M16A4 FSB is .072" taller than the A1 FSB. I guess the A2 FSB comes in right between the two
I don't think you can just go by the position of the rear sight screw because the A1 and A2 apertures are different heights |
|
|
|
Posted: 4/17/2023 7:33:35 AM EDT
[#14]
Quote HistoryQuoted: That 0.103” is a plausible number for the difference in shelf height, but the difference in the actual height of the sights is less than that because on a carry-handle sight the windage screw sits lower in the sight base than it does on the corresponding A2 part. Measuring the examples I have on hand, the A2 windage screw is only about 0.050” lower (relative to the bottom of the receiver) than with a carry handle and flattop receiver. The difference between the sight bases is visible by eye. One point I’m not clear on is how the aperture heights above the windage screw compare on A1 vs A2. The height of the windage screw seems to be the same, and yet the A2 uses an FSB that’s ~0.032 higher than the A1. Any thoughts? There is the 0.0103" difference (carry handle higher) to the bore centerline to the top of the rear sight base shelf. Then the difference in height to the rear sight windage axis in the rear sight base is exactly 0.060" (M16A2 higher), so the total sight line of the carry handle is 0.040" higher, almost exactly the same height the front sight shelf moved up on the "F" front sight. As to the M16A2: Not only is the front sight shelf on the M16A2 0.040" higher than the M16A1, the front sight post is a tiny bit (0.005") taller too, The height to the rear sight windage axis for the M16A1 is 2.252. The height to the rear sight windage axis for the M16A2 with the rear sight base run all the way down is 2.253". The reason the front sight shelf moved up has to do with the changes made to the front sight post. Not only did the sighting post get 0.005" taller, the threaded portion got 0.080" longer as well. In order to keep the threads from poking out the bottom of its little swell on the forging, the top of the shelf had to be moved up. This also allowed the rear sight to be a few click above contact when zeroed at 300, so you can lower the sight for 200 dope (USMC qualification). Why did they make the threads longer? I am not sure, but I'll bet the "accuracy shooter" camp did not not like the amount of play in the front sight post threads and wanted a longer bearing surface. (it is a class 2 thread) |
|
|
|
Posted: 4/17/2023 7:38:49 AM EDT
[#15]
Quote HistoryQuoted: Poking around the TDPs, the M4/M4A1/M16A4 FSB is .072" taller than the A1 FSB. I guess the A2 FSB comes in right between the two I don't think you can just go by the position of the rear sight screw because the A1 and A2 apertures are different heights The short range aperture for the M16A1 is 0.310" above the windage screw axis. The long range aperture for the M16A1 is 0.324" above the windage screw axis. The 0-2 aperture for the M16A2/M4 is 0.312" above the windage screw axis. The small aperture for the M16A2/M4 is 0.327" above the windage screw axis. Yeah, you can use the rear sight windage screw as a reference, 0.002 to 0.003 inch is well within the tolerances. |
|
|
|
Posted: 4/17/2023 9:02:18 AM EDT
[#16]
Quote HistoryQuoted: If you measure the height above the bore centerline of a A2 upper to the shelf the rear sight base rests on when fully down, it is 1.948" If you measure from the bore centerline to the top of the rail on an M4 the height is 1.218". If you measure the height from the seating plane of the handle rail to the shelf for the rear sight base, the height is 0.833" giving a total distance of 2.051" So, the M4 with a carry handle moves the position of the rear sight up a full 0.103". The F "Front Sight", P/N 12972681, (the correct term for what everyone incorrectly refers to as the FSB) is taller to the sight shelf because the rear sight is taller. But notice the front isnt bumped up as much as rear, so effectively carbine 14.5 sight is SHORTER |
|
|
|
Posted: 4/17/2023 9:03:51 AM EDT
[#17]
Quote HistoryQuoted: That 0.103” is a plausible number for the difference in shelf height, but the difference in the actual height of the sights is less than that because on a carry-handle sight the windage screw sits lower in the sight base than it does on the corresponding A2 part. Measuring the examples I have on hand, the A2 windage screw is only about 0.050” lower (relative to the bottom of the receiver) than with a carry handle and flattop receiver. The difference between the sight bases is visible by eye. One point I’m not clear on is how the aperture heights above the windage screw compare on A1 vs A2. The height of the windage screw seems to be the same, and yet the A2 uses an FSB that’s ~0.032 higher than the A1. Any thoughts? Someone needs to measure bottom of upper to aperture, using a 'height stand' gauge |
|
|
|
Posted: 4/17/2023 9:07:08 AM EDT
[#18]
Someone needs to figure out the drop between the aperture and post on a 14.5 m4 carbine, and that will tell you exactly how much shorter the a4 would have to be to be on the same line. Maybe the location of the front alone is easily compensated by a few clicks of the front sight post.
|
|
|
|
Posted: 4/17/2023 9:10:25 AM EDT
[#19]
My dream gun is a no-fa no-bump m16 upper carbine with m4 feed ramps, modern forged 14.5" pencil carbine p/w
I have a carbine that does not zero very well, which post should I buy for more height? |
|
|
|
Posted: 4/17/2023 9:28:21 AM EDT
[#20]
I have to wonder why Colt didn't just go with a shorter rear sight height on their carry handles like the commercial manufacturers did? To my mind it makes a heck of a lot more sense than changing the front sight base. But maybe I'm overlooking something?
|
|
|
|
Posted: 4/17/2023 10:30:12 AM EDT
[#21]
Quote HistoryQuoted: I have to wonder why Colt didn't just go with a shorter rear sight height on their carry handles like the commercial manufacturers did? To my mind it makes a heck of a lot more sense than changing the front sight base. But maybe I'm overlooking something? https://i.imgur.com/q4eaON6l.jpg That's a fantastic question. This proves that they did not need to raise the sites. Maybe it was just a concurrent change that was not driven by the removable handle, but rather they just decided heigher sights are better. |
|
|
|
Posted: 4/17/2023 10:33:19 AM EDT
[#22]
Quote HistoryQuoted: Someone needs to figure out the drop between the aperture and post on a 14.5 m4 carbine, and that will tell you exactly how much shorter the a4 would have to be to be on the same line. Maybe the location of the front alone is easily compensated by a few clicks of the front sight post. |
|
|
|
Posted: 4/17/2023 2:24:57 PM EDT
[#23]
Quote HistoryQuoted: But notice the front isnt bumped up as much as rear, so effectively carbine 14.5 sight is SHORTER For the nominal dimensions M16A2: Centerline of bore to rear sight base shelf = 1.948 Bottom of rear sight base to windage axis centerline = 0.305 Total height at rear sight = 2.253 Front sight shelf height above bore centerline = 2.325 M4: Centerline of bore to carry handle seat plane = 1.218 Carry handle seat plane to rear sight base shelf = 0.833 Bottom of rear sight base to windage axis centerline =0.245 Total height at rear sight = 2.296 Front sight shelf height above bore centerline = 2.357 Difference at the rear sight = the M4 rear sight is 0.043 higher Difference at the front sight = the M4 rear sight is 0.032 higher If you go and throw in all the possible tolerances The heights are going to be within the same band. That 0.011 difference is two (2) clicks on the front sight of either, two (2) clicks on the rear sight elevation knob on the M16A2, or four (4) clicks on the M4 rear sight elevation knob. Just as sanity check, the height of the aperture to the seat plane on the MBUS set at 300 meters is 1.414" (plus or minus), the height of the aperture of the carry handle from the seat plane when set at 300 is 1.390". |
|
|
|
Posted: 4/17/2023 2:27:28 PM EDT
[#24]
Quote HistoryQuoted: Someone needs to measure bottom of upper to aperture, using a 'height stand' gauge Why, you can add up the dimensions from the drawings . . . |
|
|
|
Posted: 4/17/2023 2:30:13 PM EDT
[#25]
Quote HistoryQuoted: I have to wonder why Colt didn't just go with a shorter rear sight height on their carry handles like the commercial manufacturers did? To my mind it makes a heck of a lot more sense than changing the front sight base. But maybe I'm overlooking something? https://i.imgur.com/q4eaON6l.jpg I think the original upper forging had a lower top rail, and they designed the carry handle to go with that. Then the Picatinny rail was standardized and the slots in the rail got deeper and the web between the inside and outside was too thin so then moved the top of the rail up. |
|
|
|
Posted: 4/17/2023 4:27:19 PM EDT
[#26]
Quote HistoryQuoted: I think the original upper forging had a lower top rail, and they designed the carry handle to go with that. Then the Picatinny rail was standardized and the slots in the rail got deeper and the web between the inside and outside was too thin so then moved the top of the rail up. This is exactly what happened. It's in the book "The Black Rifle 2". Richard Swan pointed out that a pencil point could be pushed through the top of the original flat top receiver because it was too thin. |
|
|
|
Posted: 4/17/2023 7:38:11 PM EDT
[#27]
Quote HistoryQuoted: This is exactly what happened. It's in the book "The Black Rifle 2". Richard Swan pointed out that a pencil point could be pushed through the top of the original flat top receiver because it was too thin. So you're saying that the carry handle was already designed, and probably was the same height as the A2… And then, when they found out the receiver was too thin and made it taller, without shortening carry handle. Not only is that super disappointing, and really not great logistically since they do refurbish rifles with new barrels, but I'm also incredibly disappointed that they went into production with this thin wall problem. |
|
|
|
Posted: 4/17/2023 7:42:27 PM EDT
[#28]
Quote HistoryQuoted: But why? The M16A4 and M4 use the same FSB Quote HistoryQuoted: Quoted: Someone needs to figure out the drop between the aperture and post on a 14.5 m4 carbine, and that will tell you exactly how much shorter the a4 would have to be to be on the same line. Maybe the location of the front alone is easily compensated by a few clicks of the front sight post. I bet they don't zero with the post on the same position though and the post ends up, screwed in deeper on the 20". The only way that's not the case is if you start talking about the dynamics of the barrel recoiling during firing as mentioned before |
|
|
|
Posted: 4/17/2023 8:46:19 PM EDT
[#29]
Quote HistoryQuoted: I bet they don't zero with the post on the same position though and the post ends up, screwed in deeper on the 20". The only way that's not the case is if you start talking about the dynamics of the barrel recoiling during firing as mentioned before Quote HistoryQuoted: Quoted: Quoted: Someone needs to figure out the drop between the aperture and post on a 14.5 m4 carbine, and that will tell you exactly how much shorter the a4 would have to be to be on the same line. Maybe the location of the front alone is easily compensated by a few clicks of the front sight post. I bet they don't zero with the post on the same position though and the post ends up, screwed in deeper on the 20". The only way that's not the case is if you start talking about the dynamics of the barrel recoiling during firing as mentioned before There's a saying I like for discussions like this: "A difference that makes no difference, is no difference" |
|
|
|
Posted: 4/17/2023 9:15:38 PM EDT
[#30]
Quote HistoryQuoted: So you're saying that the carry handle was already designed, and probably was the same height as the A2… And then, when they found out the receiver was too thin and made it taller, without shortening carry handle. Not only is that super disappointing, and really not great logistically since they do refurbish rifles with new barrels, but I'm also incredibly disappointed that they went into production with this thin wall problem. The original mounting system was more like a Weaver mount with shallow radius cuts, and to redo the carry handle forging was an expensive proposition. So why wasn't redoing the upper forging an expensive proposition? Because the original forging for the uppers was a dual purpose forging that had enough meat on it to machine the rails or machine the carry handle. |
|
|
|
Posted: 4/17/2023 11:25:29 PM EDT
[#31]
Quote HistoryQuoted: The original mounting system was more like a Weaver mount with shallow radius cuts, and to redo the carry handle forging was an expensive proposition. Is not the only difference between a mil-spec height carry handle and a commercial height carry handle a 0.040 difference in how high they machine the shelf for the rear sight to bottom out on? Not that it's a different forging altogether? |
|
|
|
Posted: 4/18/2023 7:09:15 AM EDT
[#32]
So if I get a C7 opera and try to throw my DD lw 14.5 carbine bbl on it, ill have to bury the post...
Still, hoping somebody's gonna tell me which post part number to buy to extend my sight on one of my guns. It's a DSA barrel, shelf height is somewhere between a2 and F, and almost the whole post skirt protrudes to zero |
|
|
|
Posted: 4/18/2023 8:28:31 AM EDT
[#33]
Quote HistoryQuoted: The original mounting system was more like a Weaver mount with shallow radius cuts, and to redo the carry handle forging was an expensive proposition. So why wasn't redoing the upper forging an expensive proposition? Because the original forging for the uppers was a dual purpose forging that had enough meat on it to machine the rails or machine the carry handle. Quote HistoryQuoted: Quoted: So you're saying that the carry handle was already designed, and probably was the same height as the A2… And then, when they found out the receiver was too thin and made it taller, without shortening carry handle. Not only is that super disappointing, and really not great logistically since they do refurbish rifles with new barrels, but I'm also incredibly disappointed that they went into production with this thin wall problem. The original mounting system was more like a Weaver mount with shallow radius cuts, and to redo the carry handle forging was an expensive proposition. So why wasn't redoing the upper forging an expensive proposition? Because the original forging for the uppers was a dual purpose forging that had enough meat on it to machine the rails or machine the carry handle. I'm not sure which was designed first, the receiver or the detachable sight/handle. I would have to go back and research that. But, the receiver was still in the development stage, not a production item when the thin "roof" was pointed out. They raised the rail .040" as a result. The front sight base machining was raised .040" to compensate for this. Hence the "F" sight base. The rest is like lysanderxiii describes above. The lower shelf commercial carry handles are the result of one or more companies wanting to use up, or keep using barrels with standard height front sight bases. So, they just machine the carry handle .040" lower. That way they can use the same barrels with fixed sight or flat top upper receivers. |
|
|
|
Posted: 4/18/2023 8:28:46 AM EDT
[#34]
Quote HistoryQuoted: Is not the only difference between a mil-spec height carry handle and a commercial height carry handle a 0.040 difference in how high they machine the shelf for the rear sight to bottom out on? Not that it's a different forging altogether? There is also the issue of the length of the screw thread portion of the rear sight base. The threads on the rear sight base bottom out on the top of the rail, so if the shelf in lowered, the thread portion is shortened and some elevation is lost. This length is shortener for the commercial carry handles. It is a cascade effect, one little change triggers a whole bunch of other changes. Raising the height of the rail, and the shelf on the front sight required the least changes other parts |
|
|
|
Posted: 4/18/2023 9:31:53 AM EDT
[#35]
Quote HistoryQuoted: There is also the issue of the length of the screw thread portion of the rear sight base. The threads on the rear sight base bottom out on the top of the rail, so if the shelf in lowered, the thread portion is shortened and some elevation is lost. This length is shortener for the commercial carry handles. It is a cascade effect, one little change triggers a whole bunch of other changes. Raising the height of the rail, and the shelf on the front sight required the least changes other parts Quote HistoryQuoted: Quoted: Is not the only difference between a mil-spec height carry handle and a commercial height carry handle a 0.040 difference in how high they machine the shelf for the rear sight to bottom out on? Not that it's a different forging altogether? There is also the issue of the length of the screw thread portion of the rear sight base. The threads on the rear sight base bottom out on the top of the rail, so if the shelf in lowered, the thread portion is shortened and some elevation is lost. This length is shortener for the commercial carry handles. It is a cascade effect, one little change triggers a whole bunch of other changes. Raising the height of the rail, and the shelf on the front sight required the least changes other parts I knew I had to be missing something.  Back in 2003 I did own a Bushmaster post ban (no flash suppressor or bayonet lug) 20" HBAR flat top, it was my first ever gun purchase and my first AR. It did come with a detachable carry handle with the typical 300 to 600 meter elevation dial. I assume that this was a commercial height carry handle since Bushmaster is the one that started that idea and still continues to do so as Windham Weaponry. However, I can't recall with 100% certainty if I could actually raise the elevation all the way to 600 meters on the dial or not.  I almost feel the need to buy a Windham Weaponry carry handle to find out, but I'm a bit short in the gun fund after my parts buying frenzy over the last 2 months preparing for the upcoming ban. 
|
|
|
|
Posted: 4/18/2023 9:52:32 AM EDT
[#36]
Quote HistoryQuoted: So if I get a C7 opera and try to throw my DD lw 14.5 carbine bbl on it, ill have to bury the post... Still, hoping somebody's gonna tell me which post part number to buy to extend my sight on one of my guns. It's a DSA barrel, shelf height is somewhere between a2 and F, and almost the whole post skirt protrudes to zero On the C7 upper with the DD carbine barrel (assumed "F" height FSB) it might zero for elevation fine. So if it were me, I'd just try zeroing and see how it goes before changing out anything. On the DSA barrel I'd either try a Colt 9mm front sight post and if it's still too high I'd then try a Windham .040 taller front sight post. Or you could just start with the .040 front sight post. |
|
|
|
Posted: 4/18/2023 12:11:34 PM EDT
[#37]
Quote HistoryQuoted: There is also the issue of the length of the screw thread portion of the rear sight base. The threads on the rear sight base bottom out on the top of the rail, so if the shelf in lowered, the thread portion is shortened and some elevation is lost. This length is shortener for the commercial carry handles. On the milspec parts, the shelf is .833 -.004 high and the elevation screw is .782 -.005 long, so with the sight cranked all the way down there’s still a bit of space there between the bottom of the screw and the top of the rail, something like .047 to .056. My commercial handle uses it: the shelf is lowered to .792, but that still exceeds the screw length, so things work out ok. There’s a clearance of .013 left underneath with the sight bottomed out. I had kinda figured there would be a price to pay in terms of elevation travel, but no: if anything it has a smidge more than my milspec example, about .100 vs .090. It’ll go from “3” all the way around to “6” with 3 clicks to spare, even though I’ve set it up with 7 or 8 clicks of RIBZ offset. One peculiar thing that I noticed about this commercial handle is that instead of having 24 elevation clicks per turn, it has 25 (like an A2!). The thread pitch seems standard (~ .074 per turn). |
|
|
|
Posted: 4/18/2023 4:08:55 PM EDT
[#38]
So, it seems like in this thread we are learning that Colt made a dumb move in raising the height of the FSB higher than A2 spec instead of addressing the rear sight shelf height of their detachable carry handle. The problem is that all back up iron sight manufacturers followed Colt's lead and designed their rear sights to match the height of the Colt/mil-spec "F" height front sight.
In the end you just have to know what you have and work with it. Most combinations are easily corrected by simply swapping the front sight post. But you can run into the issue of having to lower your front sight post very far down into the FSB if you are using a fixed carry handle upper in combination with an "F" height FSB, or if you are using a commercial height detachable carry handle in combination with an "F" height FSB. So at least try to avoid those two combinations... Though that might only be the case with rifle length sight radius configurations and not for carbines. |
|
|
|
Posted: 4/18/2023 8:27:42 PM EDT
[#39]
Quote HistoryQuoted: On the C7 upper with the DD carbine barrel (assumed "F" height FSB) it might zero for elevation fine. So if it were me, I'd just try zeroing and see how it goes before changing out anything. On the DSA barrel I'd either try a Colt 9mm front sight post and if it's still too high I'd then try a Windham .040 taller front sight post. Or you could just start with the .040 front sight post. Is c7 sight same height as m16? |
|
|
|
Posted: 4/18/2023 8:31:01 PM EDT
[#40]
Quote HistoryQuoted: So, it seems like in this thread we are learning that Colt made a dumb move in raising the height of the FSB higher than A2 spec instead of addressing the rear sight shelf height of their detachable carry handle. The problem is that all back up iron sight manufacturers followed Colt's lead and designed their rear sights to match the height of the Colt/mil-spec "F" height front sight. In the end you just have to know what you have and work with it. Most combinations are easily corrected by simply swapping the front sight post. But you can run into the issue of having to lower your front sight post very far down into the FSB if you are using a fixed carry handle upper in combination with an "F" height FSB, or if you are using a commercial height detachable carry handle in combination with an "F" height FSB. So at least try to avoid those two combinations... Though that might only be the case with rifle length sight radius configurations and not for carbines. ie the carbine post should be a tad higher than rifle, so it may be more forging. Still, kinda blows up my plans for that barrel. |
|
|
|
Posted: 4/18/2023 8:48:35 PM EDT
[#41]
Quote HistoryQuoted: Is c7 sight same height as m16? Yes |
|
|
|
Posted: 4/18/2023 9:09:39 PM EDT
[#42]
Quote HistoryQuoted: Yes Quote HistoryQuoted: Quoted: Is c7 sight same height as m16? Yes What he said. ^^^ Same sight. |
|
|
|
Posted: 4/18/2023 9:15:40 PM EDT
[#43]
Quote HistoryQuoted: ie the carbine post should be a tad higher than rifle, so it may be more forgiving. Still, kinda blows up my plans for that barrel. Quote HistoryQuoted: Quoted: So, it seems like in this thread we are learning that Colt made a dumb move in raising the height of the FSB higher than A2 spec instead of addressing the rear sight shelf height of their detachable carry handle. The problem is that all back up iron sight manufacturers followed Colt's lead and designed their rear sights to match the height of the Colt/mil-spec "F" height front sight. In the end you just have to know what you have and work with it. Most combinations are easily corrected by simply swapping the front sight post. But you can run into the issue of having to lower your front sight post very far down into the FSB if you are using a fixed carry handle upper in combination with an "F" height FSB, or if you are using a commercial height detachable carry handle in combination with an "F" height FSB. So at least try to avoid those two combinations... Though that might only be the case with rifle length sight radius configurations and not for carbines. ie the carbine post should be a tad higher than rifle, so it may be more forgiving. Still, kinda blows up my plans for that barrel. Correct. |
|
|
|
Posted: 4/19/2023 6:25:15 AM EDT
[#44]
Quote HistoryQuoted: What he said. ^^^ Same sight. Quote HistoryQuoted: Quoted: Quoted: Is c7 sight same height as m16? Yes What he said. ^^^ Same sight. I wonder if u can just mill off .040", or if the whole pocket is shifted down .040" |
|
|
|
Posted: 4/19/2023 9:49:07 AM EDT
[#45]
Quote HistoryQuoted: I wonder if u can just mill off .040", or if the whole pocket is shifted down .040" Quote HistoryQuoted: Quoted: Quoted: Quoted: Is c7 sight same height as m16? Yes What he said. ^^^ Same sight. I wonder if u can just mill off .040", or if the whole pocket is shifted down .040" That I don't know, but I'd assume that the pocket for both the front sight and it's detent would be adjusted between an A2 height FSB's shelf and an "F" height FSB's shelf so that the depth would be the same. |
|
|
|
Posted: 4/19/2023 11:08:47 AM EDT
[#46]
Quote HistoryQuoted: That I don't know, but I'd assume that the pocket for both the front sight and it's detent would be adjusted between an A2 height FSB's shelf and an "F" height FSB's shelf so that the depth would be the same. Quote HistoryQuoted: Quoted: I wonder if u can just mill off .040", or if the whole pocket is shifted down .040" That I don't know, but I'd assume that the pocket for both the front sight and it's detent would be adjusted between an A2 height FSB's shelf and an "F" height FSB's shelf so that the depth would be the same. Looking at the TDP for the front sight base, the pocket is dimensioned from the shelf, not from the centerline of the barrel. So, the pocket moved with the shelf. |
|
|
|
Posted: 4/19/2023 12:09:34 PM EDT
[#47]
Quote HistoryQuoted: Looking at the TDP for the front sight base, the pocket is dimensioned from the shelf, not from the centerline of the barrel. So, the pocket moved with the shelf. Quote HistoryQuoted: Quoted: Quoted: I wonder if u can just mill off .040", or if the whole pocket is shifted down .040" That I don't know, but I'd assume that the pocket for both the front sight and it's detent would be adjusted between an A2 height FSB's shelf and an "F" height FSB's shelf so that the depth would be the same. Looking at the TDP for the front sight base, the pocket is dimensioned from the shelf, not from the centerline of the barrel. So, the pocket moved with the shelf. Makes sense, that's what I was assuming to be the case. |
|
|
|
Posted: 4/19/2023 5:46:27 PM EDT
[#48]
Colt Front Sight Posts
Colt has produced at least four different front sight posts for use on their AR-15/M16/M4 series of weapons. The front sight posts can be roughly categorized according to their basic shape, (square or round) their profile, (straight or tapered) and their height of the post above the "flange", (short or tall.) The height of the posts are measured from the top of the sight post down to the top of the flange of the sight post. The sight post with the part number SP64507 has a short, square and straight configuration. This post has a measured nominal height of approximately 0.270” SP64507  Part number SP64665 also has a short and square post, but differs from the above sight post in that it has a tapered shape to it; broader at the base and narrowing at the top. The measured nominal height of this post is also approximately 0.270”. SP64665  Shown below are the square, short/straight and short/tapered sight posts side by side for comparison.  The sight post associated with the M16/M16A1 series of rifles has a round shape and is also short and tapered. The part number for this post is SP61706. It is slightly shorter than the two posts described above with a measured nominal height of approximately 0.260”. SP61706  The last sight post is Colt’s tall sight post which has a measured nominal height of approximately 0.300”. It has a square and straight configuration. Its part number is SP62447. SP62447  Here is a pic with the round sight post and the tall sight post side by side for comparison.  The original round sight post has five equally spaced notches around the sight post flange for elevation adjustment. Each notch corresponds to approximately 1 MOA of elevation (when used with a rifle length sight radius). The other three sight posts all have four elevation notches on their flanges corresponding to approximately 1.25 MOA of evlevation (with the rifle length sight radius).  |
|
|
|
Posted: 4/19/2023 9:20:18 PM EDT
[#49]
Quote HistoryQuoted: Colt Front Sight Posts Colt has produced at least four different front sight posts for use on their AR-15/M16/M4 series of weapons. The front sight posts can be roughly categorized according to their basic shape, (square or round) their profile, (straight or tapered) and their height of the post above the "flange", (short or tall.) The height of the posts are measured from the top of the sight post down to the top of the flange of the sight post. The sight post with the part number SP64507 has a short, square and straight configuration. This post has a measured nominal height of approximately 0.270” SP64507 https://www.ar15.com/media/mediaFiles/28568/short_straight_front_sight_post_01_resiz-1302034.jpg Part number SP64665 also has a short and square post, but differs from the above sight post in that it has a tapered shape to it; broader at the base and narrowing at the top. The measured nominal height of this post is also approximately 0.270”. SP64665 https://www.ar15.com/media/mediaFiles/28568/short_tapered_sight_post_01_resized-1302035.jpg Shown below are the square, short/straight and short/tapered sight posts side by side for comparison. https://www.ar15.com/media/mediaFiles/28568/short_straight_and_tapered_sight_posts_0-1302037.jpg The sight post associated with the M16/M16A1 series of rifles has a round shape and is also short and tapered. The part number for this post is SP61706. It is slightly shorter than the two posts described above with a measured nominal height of approximately 0.260”. SP61706 https://www.ar15.com/media/mediaFiles/28568/round_front_sight_post_01_resized-1302040.jpg The last sight post is Colt’s tall sight post which has a measured nominal height of approximately 0.300”. It has a square and straight configuration. Its part number is SP62447. SP62447 https://www.ar15.com/media/mediaFiles/28568/colt_tall_front_sight_post_01_resized-1302038.jpg Here is a pic with the round sight post and the tall sight post side by side for comparison. https://www.ar15.com/media/mediaFiles/28568/colt_tall_post_and_round_post_01_resized-1302039.jpg The original round sight post has five equally spaced notches around the sight post flange for elevation adjustment. Each notch corresponds to approximately 1 MOA of elevation (when used with a rifle length sight radius). The other three sight posts all have four elevation notches on their flanges corresponding to approximately 1.25 MOA of evlevation (with the rifle length sight radius). https://www.ar15.com/media/mediaFiles/28568/elevation_notches_on_front_sight_posts_0-1302042.jpg That's super, thank you! But i have a follow up q. If 4 notch is 1.25 moa on rifle, which will be even coarser on a carbine, how the hell do you fine tune your zero. |
|
|
|
Posted: 4/20/2023 2:40:00 AM EDT
[#50]
Quote HistoryQuoted: That's super, thank you! But i have a follow up q. If 4 notch is 1.25 moa on rifle, which will be even coarser on a carbine, how the hell do you fine tune your zero. |
|
|
Win a FREE Membership!
Sign up for the ARFCOM weekly newsletter and be entered to win a free ARFCOM membership. One new winner* is announced every week!
You will receive an email every Friday morning featuring the latest chatter from the hottest topics, breaking news surrounding legislation, as well as exclusive deals only available to ARFCOM email subscribers.
AR15.COM is the world's largest firearm community and is a gathering place for firearm enthusiasts of all types.
From hunters and military members, to competition shooters and general firearm enthusiasts, we welcome anyone who values and respects the way of the firearm.
Subscribe to our monthly Newsletter to receive firearm news, product discounts from your favorite Industry Partners, and more.
Copyright © 1996-2024 AR15.COM LLC. All Rights Reserved.
Any use of this content without express written consent is prohibited.
AR15.Com reserves the right to overwrite or replace any affiliate, commercial, or monetizable links, posted by users, with our own.
