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Posted: 9/17/2005 4:17:37 PM EDT
[Last Edit: 9/17/2005 8:25:19 PM EDT by 556Cliff]
I just got to know why?
Link Posted: 9/17/2005 4:48:33 PM EDT
Because it takes more metal to have a removable carry handle hence forcing the rear sights to be higher hence forcing the front sight to be higher. Does this make sence I am not the most articulate poster here.
Pat
Link Posted: 9/17/2005 5:48:38 PM EDT
Link Posted: 9/17/2005 6:05:01 PM EDT

Originally Posted By Glockfan:
Because it takes more metal to have a removable carry handle hence forcing the rear sights to be higher hence forcing the front sight to be higher. Does this make sence I am not the most articulate poster here.
Pat



They why don't all flat tops require taller front sights?

Link Posted: 9/17/2005 6:22:02 PM EDT
Like I said because the carry handle is taller because its removable metal had to be added. Hence making the front sight taller to stay in alignment.
Pat
Link Posted: 9/17/2005 6:46:13 PM EDT

Originally Posted By ian187:

Originally Posted By Glockfan:
Because it takes more metal to have a removable carry handle hence forcing the rear sights to be higher hence forcing the front sight to be higher. Does this make sence I am not the most articulate poster here.
Pat



They why don't all flat tops require taller front sights?




They do. Some manufacturers use sandard height on flat top carbines because they are too cheap to have 2 different parts. Many of these rifles have posts that stick up higher than the protective ears.
Link Posted: 9/17/2005 6:53:26 PM EDT
Link Posted: 9/17/2005 8:18:35 PM EDT
[Last Edit: 9/17/2005 8:42:10 PM EDT by 556Cliff]

Originally Posted By Tweak:
ar15.com/forums/topic.html?b=3&f=66&t=240121



OK, after reading all of that I'm too confused to understand why Mil-Spec front and rear sights are taller then the rest.

So instead of trying to understand why Mil-Spec sights are taller, lets just have someone make a list of the companys that make the correct Mil-Spec highth front sight bases, flat top uppers and removable carry handles. Also there should be a list of who makes the out of spec front sight bases, flat top uppers and removable carry handles. You know, so we can avoid the crap.

Anyone want to make that list?



Also, I would like to know if Bushmaster flat top uppers and A3 carry handles are in spec. Does anyone know the answer to that?

And last, what actually is the taller part on an in spec removable carry handle? The carry handle itself, or the rear sight base that raises up and down?

And I'm I right that it's the highth of the rails on the flat top upper that make it in spec or out of spec?

My head hurts.
Link Posted: 9/17/2005 8:27:46 PM EDT
[Last Edit: 9/17/2005 8:28:27 PM EDT by BravoCompanyUSA]
Link Posted: 9/17/2005 8:58:40 PM EDT

Originally Posted By BravoCompanyUSA:

Originally Posted By 556Cliff:
So instead of trying to understand why Mil-Spec sights are taller, lets just have someone make a list of the companys that make the correct Mil-Spec highth front sight bases, flat top uppers and removable carry handles. Also there should be a list of who makes the out of spec front sight bases, flat top uppers and removable carry handles. You know, so we can avoid the crap.

Anyone want to make that list?



Makers of uppers with F-FSB:
Colt
LMT
CMT/Stag
BCM
GTS

If your barrel or the barrel of a maker not listed above does not have the Mil-Spec FSB it is not a big deal. The difference is only .032" and can be corrected with a taller front sight post sold by Bushmaster or DPMS for about $5


Makers of Rear sights of Mil-Spec heights.
Colt
LMT
CMT
KAC
ARMS
MIYHM ?
Troy Ind
GG&G (although I heard the DEA issue BUIS was shorter - special run)

. . .sorry if I forgot some



Thanks for posting some of the info you have.

You don't need a taller front sight post if your not useing a Mil-Spec rear sight do you? Because I use a Bushmaster A3 carry handle wich should be out of spec according to your list and it works fine with the standard front sight base and sight post.
Link Posted: 9/17/2005 9:13:52 PM EDT
[Last Edit: 9/17/2005 9:14:17 PM EDT by BravoCompanyUSA]
Link Posted: 9/18/2005 7:07:02 AM EDT
The Bushie detachable on my M4gery measures within a couple of thousanths of the Colt dimensions on Tweak's post; and BTW, thanks for reposting that info Tweak. I'd lost it.

It sits on a Conti upper, and requires a .040 higher front post on the Rock River barrel. I suppose if I'd bought a Colt barrel, I could have used a atandard post w/the F marked base.


Now here's the thing. All these "Colt and mil spec flat flat tops need a higher front sight point " threads conveniently ignore one little fact. The carbines and SMGs with one piece uppers also need a higher front sight. SHORT BARREL ARs HAVE ALWAYS NEEDED A HIGHER FRONT SIGHT.

My Colt SP1 carbine came with a .040 higher front sight in 1978, and when I replaced it with a square profile type awhile back I had to get one of Bushie's .040 higher replacements.

Now my own rather crude measurements, which I did from the top of the charging handle channel to the (approximate) center of the lower aperture indicated no significant differences between that dimension in an A1 profile upper (Colt) and the upper/sight combo mentioned above. Since I don't currently have a rifle w/an A2 profile upper, I couldn't do a measurement on that type, but I'm willing to bet it's not that much different.

Given that the same few forges are currently turning out raw forgings for all the major suppliers, including Colt, I've got to believe that the bottom to top dimensions on all the flat top/sight unit pieces are pretty much the same for all the major manufacturers these days. Now depth of the cutouts may have significant differences, but that's a different issue.

Until someone who owns a flat top 20" barrelled rifle, with upper and sight assy made in the past three years by a major manufacturer, posts that he needed a higher front sight to get zeroed, I'll continue to believe that the "higher front sight point need" is a function of shorter barrel/ gas system length and not what type of upper one has.

And yes, I am aware that Colt, and FN, are putting F marked bases on their rifles now. So what? You can screw down the post to the right height easily enough, and you can save a few bucks in machining costs by using the same base for everything.
Link Posted: 9/18/2005 8:15:27 AM EDT
So which height does a mid-length gas system require, tall or "regular"?
Link Posted: 9/18/2005 8:16:52 AM EDT
[Last Edit: 9/18/2005 8:20:03 AM EDT by txgp17]
IIRC, COLT MIL-SPEC rifles call for higher FSB because the carrying handle is taller. FN, who makes the A4's from Colt's blueprints, does the same thing.
Link Posted: 9/18/2005 10:34:57 AM EDT

Originally Posted By bolster:
So which height does a mid-length gas system require, tall or "regular"?


The length of the gas system has nothing to do with it.
Link Posted: 9/18/2005 11:20:12 AM EDT

Originally Posted By Hoplophile:

Originally Posted By bolster:
So which height does a mid-length gas system require, tall or "regular"?


The length of the gas system has nothing to do with it.



Some are saying it is a carbine-gas system thing and others are saying it's the upper, so I just wanted to know which FSB manufacturers are using for their mid-length uppers. Since there's probably no standard, maybe I asked a question to which there is no answer.

I guess it really depends more on what height your rear sight is, which depends on the carrying handle from what I gather, but then if you read Shamayim's post, "Now here's the thing. All these "Colt and mil spec flat flat tops need a higher front sight point " threads conveniently ignore one little fact. The carbines and SMGs with one piece uppers also need a higher front sight. SHORT BARREL ARs HAVE ALWAYS NEEDED A HIGHER FRONT SIGHT." - it becomes ambiguous. Why did they always require a taller front sight? Should a midlength then require something in the middle between an "f" marked and "standard" FSB?
Link Posted: 9/18/2005 11:28:43 AM EDT
[Last Edit: 9/18/2005 11:41:21 AM EDT by 556Cliff]

Originally Posted By txgp17:
IIRC, COLT MIL-SPEC rifles call for higher FSB because the carrying handle is taller. FN, who makes the A4's from Colt's blueprints, does the same thing.



Is the reason Colts 20" barrel rifles have the taller FSBs and RSBs because of the Carbines need for taller front and rear sights and the fact that Colt didn't want 2 sets of flat top sight parts laying around even though the 20" barrel didn't need them? That's the only reason I can think of for having taller front and rear sights on rifles.

But does anyone have sight in problems with carbines that have shorter not Mil-Spec front and rear sights?

Was there ever a need for Colt to have taller front and rear sights for their carbines or was it just a Colt blooper?
Link Posted: 9/18/2005 11:30:07 AM EDT
Link Posted: 9/18/2005 11:50:55 AM EDT

Originally Posted By Gloftoe:
I think I've run into this problem with my Bushmaster 14.5" flattop upper. I tried putting an LMT BIUS on it, and had to buy the ".040 front sight post" from Bushmaster. I still had to crank it WAY up to get my elevation right. But, I have a Bushmaster 20" flattop upper that works just fine out of the box, with an ARMS #40. Bah, I don't know what to think.

Guess I'll take them both out and re-sight at 50yds, and try the ARMS 40 on the shorter upper.



That's just wierd.

If you have the taller front sight post and the LMT BUIS on your carbine that is Mil-Spec highth it should be perfect shouldn't it?

Nothing makes sense any more!
Link Posted: 9/18/2005 1:03:21 PM EDT
[Last Edit: 9/18/2005 1:03:35 PM EDT by txgp17]

Originally Posted By 556Cliff:
Is the reason Colts 20" barrel rifles have the taller FSBs and RSBs because of the Carbines need for taller front and rear sights and the fact that Colt didn't want 2 sets of flat top sight parts laying around even though the 20" barrel didn't need them? That's the only reason I can think of for having taller front and rear sights on rifles.

But does anyone have sight in problems with carbines that have shorter not Mil-Spec front and rear sights?

Was there ever a need for Colt to have taller front and rear sights for their carbines or was it just a Colt blooper?


I think it was just an issue that the detachable carrying handle that Colt designed wasn't as low as the A1 & A2 carrying handle. I can't imagine any reason in the world to not make the DCHandle the same height as the A1 & A2, except they ran into some machining and/or engineering issues and could not produce it like they wanted.
Link Posted: 9/18/2005 1:13:07 PM EDT
[Last Edit: 9/18/2005 1:16:20 PM EDT by TonyF]
Link Posted: 9/18/2005 1:14:34 PM EDT

Originally Posted By txgp17:

Originally Posted By 556Cliff:
Is the reason Colts 20" barrel rifles have the taller FSBs and RSBs because of the Carbines need for taller front and rear sights and the fact that Colt didn't want 2 sets of flat top sight parts laying around even though the 20" barrel didn't need them? That's the only reason I can think of for having taller front and rear sights on rifles.

But does anyone have sight in problems with carbines that have shorter not Mil-Spec front and rear sights?

Was there ever a need for Colt to have taller front and rear sights for their carbines or was it just a Colt blooper?


I think it was just an issue that the detachable carrying handle that Colt designed wasn't as low as the A1 & A2 carrying handle. I can't imagine any reason in the world to not make the DCHandle the same height as the A1 & A2, except they ran into some machining and/or engineering issues and could not produce it like they wanted.



No, I think you missed his question and mine too: Why did the carbine with a FIXED carrying handle have a taller front sight? That's why I'm scratching my head.
Link Posted: 9/18/2005 3:28:47 PM EDT

Originally Posted By bolster:
No, I think you missed his question and mine too: Why did the carbine with a FIXED carrying handle have a taller front sight? That's why I'm scratching my head.

You're correct, I did miss that question. Furthermore, I didn't know that fixed handle carbines had the taller FSB, I thought the "F" marked FSB were marked that way to indicate they were for flat-top rifles, of any length barrel, but that's just my assumption. I'm not much of a Colt fan, AND NOT because I think they are junk by the way, I don't want to turn this into a Colt bashing thread, it's just that I don't follow their product lines very much, but I do try to pay a little attention to what Uncle Sam is packing.
Link Posted: 9/18/2005 4:06:46 PM EDT
[Last Edit: 9/18/2005 4:07:25 PM EDT by scottryan]
There is no difference in detachable carry handle heights.

F stamped FSB are spec on anything that has a flattop. It has nothing to do with carbines and rifles.

We have go through this crap all the time. And we still have about 75% of the people spreading misinformation about it.

Why can we tack a thread or I will start a new thread latter this week explaining this whole deal with pictures that can be tacked.
Link Posted: 9/18/2005 5:03:13 PM EDT
+1 to that Scott.
Link Posted: 9/18/2005 5:45:14 PM EDT

Originally Posted By TonyF:

Originally Posted By 556Cliff:

But does anyone have sight in problems with carbines that have shorter not Mil-Spec front and rear sights?



I can't recall the details but the last carbine class we did a student had a parts gun and *ran out* of front sight adjustment. It was a 16 barrel flat top (don't know what brand) and he dd not have an F marked FSB.

ETA: He was running an optic but I can't recall which BUIS.



Well that would make sense if the BUIS he was useing was of correct MIL-SPEC highth wouldn't it?
Link Posted: 9/18/2005 5:52:12 PM EDT
Link Posted: 9/18/2005 6:04:25 PM EDT
[Last Edit: 9/18/2005 6:12:21 PM EDT by 556Cliff]

Originally Posted By scottryan:
There is no difference in detachable carry handle heights.

F stamped FSB are spec on anything that has a flattop. It has nothing to do with carbines and rifles.

We have go through this crap all the time. And we still have about 75% of the people spreading misinformation about it.

Why can we tack a thread or I will start a new thread latter this week explaining this whole deal with pictures that can be tacked.



So if there is no difference in the highth of the carry handles being used then it's got to be the rear sight bases that are of different height, right?

Still there is not much of an answer to the "WHY" question though.

+2 on the pics and a good explaination!

And what about flat top uppers? Does anyone have a list of who makes correct highth MIL-SPEC flat top upper receivers?
Link Posted: 9/18/2005 6:25:42 PM EDT
Link Posted: 9/18/2005 10:34:17 PM EDT
[Last Edit: 9/19/2005 2:49:37 AM EDT by bolster]

Originally Posted By scottryan:
There is no difference in detachable carry handle heights.

F stamped FSB are spec on anything that has a flattop. It has nothing to do with carbines and rifles.

We have go through this crap all the time. And we still have about 75% of the people spreading misinformation about it.

Why can we tack a thread or I will start a new thread latter this week explaining this whole deal with pictures that can be tacked.



Let me apologize for not being as knowledgible as you. "We" don't have to go through this crap all the time. If you see a thread discussing something that's been discussed before, no one is forcing you to get involved and read it. Just skip it if it's something you already know about, which apparently is everything, judging on your posts in other threads, where you've shown little patience with people who don't know everything that you do.

Look for instance at all the threads each week on "which FF forend to use." Yes, it's been discussed a million times and will be a million more. Just let it go. It's not like the AR changes in leeps and bounds every day, so you're gonna see the same thing discussed a lot- something you should know since you've been here a long time.

If you have information to share, and want to contribute, then please do. But please put an end to the condescending attitude, or just let the "75%" continue to misinform everyone. If people are misinformed about the height of front and rear sights, it's hardly a matter of national security.
Link Posted: 9/19/2005 10:10:58 AM EDT

Originally Posted By Tweak:

Originally Posted By scottryan:
There is no difference in detachable carry handle heights.



Wrong.



So is it the removable carry handle that has two different heights or is it the Rear Sight Base?
Link Posted: 9/19/2005 2:15:41 PM EDT
I got an E-mail from Bushmaster that said on Colt 20"A4 barrels there is two raised bands under the hand guards to point to the fact that the barrel has an F marked FSB. Can anyone else confirm this? If it is true, is it also on Colt 14.5 flat top barrels?
Link Posted: 9/19/2005 4:04:08 PM EDT
[Last Edit: 9/19/2005 4:47:03 PM EDT by scottryan]

Originally Posted By 556Cliff:
I got an E-mail from Bushmaster that said on Colt 20"A4 barrels there is two raised bands under the hand guards to point to the fact that the barrel has an F marked FSB. Can anyone else confirm this? If it is true, is it also on Colt 14.5 flat top barrels?



I don't know what they are talking about. I have a M16A4 upper in front of me and the barrel is the same and a M16A2 barrel except for an F marked FSB.

It could be something latter, as I don't think anyone on here has seen a current production M16A4 barrel recently.
Link Posted: 9/19/2005 4:11:49 PM EDT
[Last Edit: 9/19/2005 4:13:21 PM EDT by scottryan]

Originally Posted By Tweak:

Originally Posted By scottryan:
There is no difference in detachable carry handle heights.



Wrong.



Someone elses measurements from both rifle and carbines...


DCH off a 1998 M16A4 with AA forge code:

.832 carry handle forging
1.29 with rear sight

Colt DCH forge code AB:

.832
1.30

replacment Colt DCH from about 1995 forge A-6 with an ArmaLite NM rear sight:

.832
1.27

DCH off a 1995 6721 with A-1 forge code in a circle:

.832 carry handle forging
1.28 with rear sight

They look the same to me.

Link Posted: 9/19/2005 4:38:00 PM EDT
[Last Edit: 9/19/2005 4:39:01 PM EDT by BravoCompanyUSA]
Link Posted: 9/19/2005 5:00:53 PM EDT
Link Posted: 9/19/2005 5:08:59 PM EDT
[Last Edit: 9/19/2005 5:10:04 PM EDT by scottryan]

Originally Posted By Tweak:

Originally Posted By scottryan:
M16A4 with AA forge code:

Colt DCH forge code AB:

replacment Colt DCH

DCH off a 1995 6721 with A-1 forge code in a circle:



So COLT builds them all them same height. Interesting.

Too bad other makers don't.



This is why they do....

As you know, there are regular sight posts and taller sight post that Bushmaster sells.

You may ask: Why doesn't Colt use the same front sight base and just change out the different sight posts? Would that be easier?

It might be easier for us but it would create a logistics problem in the miltary. Imagine they have two different front sight posts and you cant really tell the difference between the two of them. They can be easily interchanged and be installed on the wrong gun.

This is why there are two different front sight bases. The front sight base is semi-permenatly attached and is not easily switched around. One front sight post is used, the part that can be easily changed, and it doesn't matter what weapon you install it on. No logistics problem.

The same goes for carry handles. They can be easily switched around. Here again there is the logistics problem. Rifle handle on carbine, carbine handle on rifle, big mix up, etc. That is why Colt carbine and rifle handles are the same.



Link Posted: 9/19/2005 7:05:30 PM EDT

Originally Posted By scottryan:

Originally Posted By Tweak:

Originally Posted By scottryan:
M16A4 with AA forge code:

Colt DCH forge code AB:

replacment Colt DCH

DCH off a 1995 6721 with A-1 forge code in a circle:



So COLT builds them all them same height. Interesting.

Too bad other makers don't.



This is why they do....

As you know, there are regular sight posts and taller sight post that Bushmaster sells.

You may ask: Why doesn't Colt use the same front sight base and just change out the different sight posts? Would that be easier?

It might be easier for us but it would create a logistics problem in the miltary. Imagine they have two different front sight posts and you cant really tell the difference between the two of them. They can be easily interchanged and be installed on the wrong gun.

This is why there are two different front sight bases. The front sight base is semi-permenatly attached and is not easily switched around. One front sight post is used, the part that can be easily changed, and it doesn't matter what weapon you install it on. No logistics problem.

The same goes for carry handles. They can be easily switched around. Here again there is the logistics problem. Rifle handle on carbine, carbine handle on rifle, big mix up, etc. That is why Colt carbine and rifle handles are the same.






It seems to me that Colt never should have made their FSBs higher. They should have just went with a shorter removable carry handle like DPMS, Bushmaster, Armalite, and RRA. Unless there is a reason for having higher front and rear sights
Link Posted: 9/19/2005 9:46:15 PM EDT

Originally Posted By DevL:

Originally Posted By ian187:

Originally Posted By Glockfan:
Because it takes more metal to have a removable carry handle hence forcing the rear sights to be higher hence forcing the front sight to be higher. Does this make sence I am not the most articulate poster here.
Pat



They why don't all flat tops require taller front sights?




They do. Some manufacturers use sandard height on flat top carbines because they are too cheap to have 2 different parts. Many of these rifles have posts that stick up higher than the protective ears.



Yet another reason to buy Colt Defense...
Link Posted: 9/19/2005 9:57:43 PM EDT
[Last Edit: 9/19/2005 10:08:16 PM EDT by Tweak]
Link Posted: 9/20/2005 5:08:06 AM EDT

Originally Posted By Tweak:

Originally Posted By scottryan:
That is why Colt carbine and rifle handles are the same.



No one has said there are "rifle" and "carbine" handles. There are two heights of DCHs to go along with the two heights of flattops.

I strongly suggest you read this before continuing



I already looked at that. I don't really understand what you are trying to prove. All the uppers in the list on the first page have the same height except the 3 on the bottom.
Link Posted: 9/20/2005 6:11:34 PM EDT
BTT.
Link Posted: 9/20/2005 7:35:09 PM EDT
[Last Edit: 9/20/2005 7:37:28 PM EDT by WIZZO_ARAKM14]

Originally Posted By shamayim:


Now here's the thing. All these "Colt and mil spec flat flat tops need a higher front sight point " threads conveniently ignore one little fact. The carbines and SMGs with one piece uppers also need a higher front sight. SHORT BARREL ARs HAVE ALWAYS NEEDED A HIGHER FRONT SIGHT.
Until someone who owns a flat top 20" barrelled rifle, with upper and sight assy made in the past three years by a major manufacturer, posts that he needed a higher front sight to get zeroed, I'll continue to believe that the "higher front sight point need" is a function of shorter barrel/ gas system length and not what type of upper one has.




Nope. My A2 uppered 16" m4gery from M&A Parts has a std. FSB and FSP. It is zeroed within a few clicks of flush on the FSB.

I'm your man. I bought a 20" RRA std. A4 upper at a gunshow on Oct. 31st last year from the head armorer at RRA (one of the perks in living in IL), and this is what the front site looks like right now with a RRA carry handle that was ordered a week later from RB Precision.



This is the 20" RRA A4 and the 16" A2/M4gery.



Am I a fluke? Possible.

This is just what I have in front of me.

BTW, my Sabre Defence 1/7 mid-length barrel came with an F-marked FSB. It zeroed perfectly with an ARMS #40 and a CMT flattop upper.

WIZZO
Link Posted: 9/21/2005 10:52:41 AM EDT

Originally Posted By WIZZO_ARAKM14:

Originally Posted By shamayim:


Now here's the thing. All these "Colt and mil spec flat flat tops need a higher front sight point " threads conveniently ignore one little fact. The carbines and SMGs with one piece uppers also need a higher front sight. SHORT BARREL ARs HAVE ALWAYS NEEDED A HIGHER FRONT SIGHT.
Until someone who owns a flat top 20" barrelled rifle, with upper and sight assy made in the past three years by a major manufacturer, posts that he needed a higher front sight to get zeroed, I'll continue to believe that the "higher front sight point need" is a function of shorter barrel/ gas system length and not what type of upper one has.




Nope. My A2 uppered 16" m4gery from M&A Parts has a std. FSB and FSP. It is zeroed within a few clicks of flush on the FSB.

I'm your man. I bought a 20" RRA std. A4 upper at a gunshow on Oct. 31st last year from the head armorer at RRA (one of the perks in living in IL), and this is what the front site looks like right now with a RRA carry handle that was ordered a week later from RB Precision.

img.photobucket.com/albums/v702/WIZZO_ARAKM14/DCP_0557.jpg

This is the 20" RRA A4 and the 16" A2/M4gery.

img.photobucket.com/albums/v702/WIZZO_ARAKM14/DCP_0591.jpg

Am I a fluke? Possible.

This is just what I have in front of me.

BTW, my Sabre Defence 1/7 mid-length barrel came with an F-marked FSB. It zeroed perfectly with an ARMS #40 and a CMT flattop upper.

WIZZO



I can't tell from the picture, is the top of the FSP even with the top of the ears on the FSB?

Are you sure that is a RRA carry handle and not a Colt or CMT/STAG? Have you checked to find out if your upper receiver rails are in spec? You might have one of the taller out of spec uppers?
Link Posted: 9/21/2005 12:15:25 PM EDT
I need the "F" FSB on my 16" bbl Bushmaster full upper with LaRue BUIS. I bought the taller Bushie front post which works but it just about sticks above the ears on the FSB and it's about at the limit of it's upward travel.

I actually bought an "F" FSB from Bravo Company (thanks), and I would have ADCO install it but....

It's a Bushie pencil barrel.

Because of what I've seen with this build, I think I'll have the "F" FSB installed on my AR15.com midlength barrel.
Link Posted: 9/21/2005 1:39:48 PM EDT
[Last Edit: 9/21/2005 2:01:48 PM EDT by shamayim]

Originally Posted By WIZZO_ARAKM14:

Originally Posted By shamayim:


Now here's the thing. All these "Colt and mil spec flat flat tops need a higher front sight point " threads conveniently ignore one little fact. The carbines and SMGs with one piece uppers also need a higher front sight. SHORT BARREL ARs HAVE ALWAYS NEEDED A HIGHER FRONT SIGHT.
Until someone who owns a flat top 20" barrelled rifle, with upper and sight assy made in the past three years by a major manufacturer, posts that he needed a higher front sight to get zeroed, I'll continue to believe that the "higher front sight point need" is a function of shorter barrel/ gas system length and not what type of upper one has.




Nope. My A2 uppered 16" m4gery from M&A Parts has a std. FSB and FSP. It is zeroed within a few clicks of flush on the FSB.

I'm your man. I bought a 20" RRA std. A4 upper at a gunshow on Oct. 31st last year from the head armorer at RRA (one of the perks in living in IL), and this is what the front site looks like right now with a RRA carry handle that was ordered a week later from RB Precision.

img.photobucket.com/albums/v702/WIZZO_ARAKM14/DCP_0557.jpg

This is the 20" RRA A4 and the 16" A2/M4gery.

img.photobucket.com/albums/v702/WIZZO_ARAKM14/DCP_0591.jpg

Am I a fluke? Possible.

This is just what I have in front of me.

BTW, my Sabre Defence 1/7 mid-length barrel came with an F-marked FSB. It zeroed perfectly with an ARMS #40 and a CMT flattop upper.

WIZZO



Glad you posted the pics, since they prove my point You, sir, had to crank up the front sight blade way beyond acceptable limits to get the thing zeroed. THE COLLAR AT THE BOTTOM OF THE BLADE IS NOT SUPPOSED TO SIGNIFICANTLY PROTRUDE ABOVE THE BASE!

You have an incorrectly installed wrong type front sight blade, my friend. If you're happy with it, fine, but you really need the higher blade that Bushmaster sells to have a proper installation.

A fluke? Absolutely not. Rather, just someone making do with the wrong pieces. That incorrect installation is going to happen every time someone tries to zero a short, non F base, barrel with a standard height front sight.
Link Posted: 9/21/2005 2:05:52 PM EDT
[Last Edit: 9/21/2005 2:09:52 PM EDT by WIZZO_ARAKM14]
I know I need the taller front site post. I measured it and the base of the site post is like .035" above the milled flat of the FSB.

The thing is, it's a 20" A4, not a 16" so your statement regarding FSB-heights being directly related to barrel length isn't correct.

Or am I just reading this quote wrong?

Originally Posted By shamayim:

Until someone who owns a flat top 20" barrelled rifle, with upper and sight assy made in the past three years by a major manufacturer, posts that he needed a higher front sight to get zeroed, I'll continue to believe that the "higher front sight point need" is a function of shorter barrel/ gas system length and not what type of upper one has.



WIZZO
Link Posted: 9/21/2005 5:01:18 PM EDT
The difference in carry handles b/w colt and all the others is that the shelf on which the rear sight base sits is higher on the colt DCH. BM and the others machine this shelf approx. 0.040" lower. All carry handles use the same dimensioned rear sight base and are machined from identical forgings.

As for why colt decided to go with the higher sight plane on their flattop uppers, I still haven't heard a convincing explanation. The shelf doesn't need to be as high as it is on the colt DCH's to accomodate the threaded portion of the rear sight base. Possibly, the sight plane was elevated 0.040" to make the sight adjustments fit the trajectory of m855 being fired out of a 14.5" barrel. Have heard one cynical account that colt raised the heights of the sights on the M4 so that the design was more proprietary.
Link Posted: 9/21/2005 5:15:21 PM EDT
Link Posted: 9/21/2005 5:53:42 PM EDT

Originally Posted By jason_h:
Have heard one cynical account that colt raised the heights of the sights on the M4 so that the design was more proprietary.



Wasn't that Troy?
Link Posted: 9/21/2005 6:00:40 PM EDT
[Last Edit: 9/21/2005 6:18:06 PM EDT by 556Cliff]

Originally Posted By Tweak:

Originally Posted By jason_h:
Possibly, the sight plane was elevated 0.040" to make the sight adjustments fit the trajectory of m855 being fired out of a 14.5" barrel.



The same DCH is used on the M16A4



It would be more cost effective for Colt to use the same DCH on the M16A4 as the M4 despite the fact that the trajectory of the M855 out of an M16A4 is slightly different... No? Besides, the M4 is Colt's favorite baby anyways.
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