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Posted: 3/22/2004 10:05:26 PM EDT
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I was just wondering how many of your have replaced your front sight post with the skinner NM front sight? I have a 16in carbine and I thought of getting one might help with the lack of sight radius... given this is a shorter ranged weapon would it be worth it... my gun is extremely accurate for being a 16" chromelined barrel... any negitives to getting it? At $10 or so the benifit of having a more accurate sight might come in handy... I might as well take advantage of the accuracy of my weapon? What are your thoughts? ...Jared |
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I have been trying to replicate the sight picture of a 20" A2 in a 16" carbine (i.e., smaller more precise front sight). I'm not sure if it helps offset the shorter sight radius, but the smaller (sharper defined) front sight post allows more precision at distance, with very little change in close-in sight engagement. IIRC the standard A2 sight post is 0.072". I currently have a Bushmaster 0.062" installed that is much more precise. My buddy is using the BM 0.052" and says that's even closer to the 20" sight picture. At $10 a pop from BM, give them a try! It's actually a good idea. Now I only wish I could find someone to cut me a few rear apertures with A2 sized holes but on the same plane.... (I currently use Ashley/XS same plane rear apertures but think they are a bit too big.) Corey |
I wasn't aware BM actually carried .062" and .052" front sight posts. I thought only Colt made .062". Are they anywhere on their website? The standard front sight post width is .072" with rifle sight radius. To keep the front post width to scale with the carbine sight radius it would need to be .052". 19.75" = rifle sight radius 14.5" = carbine sight radius 14.5"/19.75" = .73417 .73417 x .072" = .05286" Colt equips their carbines with .062" thick front posts. I asked why not .052" and the response I got was as you approach .050" the FSP becomes to weak for military and LEO use and they get breakages. They do not recommend going smaller than .062" for FSP width for LEO, self-defense or military use.
Try Lew Tippie @ Tippiecompetition in the industry forums, he can do it. The apertures need to be on the same verticle plane, but need to be windage offset about 2.5 clicks (assuming 1/2MOA windage screw) to account for flipping the aperture. The XS same planes are indeed bigger. .230" vs. .200" and .100" vs. .73". However, there are other more-hidden benefits of their design. The large aperture: -Not countersunk, which makes the aperture less prone to glare into the shooters' eye. Never had this problem with the A2 to be fair though. -Instead of being a half-oval it is truly round. For me this helped me to center the front sight post correctly quicker than the A2. -Larger aperture means better light transmission, this aperture will have an edge in low-light over the A2. The small aperture: -Bigger outside diameter. This allowed my eye to better center the front post quickly. It's less likely to break on impact. -Larger aperture means better light transmission, sight picture is much quicker to aquire, can be used in lower-light than small A2. Lastly, try shooting groups with the large aperture of both the A2 and the XS. Your groups won't spread by very much at all. Just because on aperture is .030" larger than another doesn't mean your eye will increase it's error by .030". Usually a .030" increase in aperture size will only increase eye perception error by .000"-.005". For instance, say your group with the A2 was 1.0" @ 50y and 1.5" @ 50y with the XS (mine didn't spread that much!). Remember carbine sight radius = 14.5" 50y=150'=1800". 1800"/14.5"=124.14 124.14 = how many times your error is replicated from 50 yards to target. .5" is how much wider your group was with XS. .5"/124.14 = .004" eye perception error increase. Everyone's needs are different, but for my intended purposes I'll take the better low-light and quicker aquisition capabilities over a slight decrease in accuracy. Now, don't get me wrong, there is a point of diminishing returns where the decreases in accuracy occur at a higher ratio in comparison to increases in speed & low-light capability. I don't think there is much to be gained by a .5" aperture.  However, I do believe, atleast for my person that the XS same-plane aperture is still within the realm of good gains in capabilities/speed for minimal accuracy cost. Besides, I need a high speed rifle to balance out my slow dragging ass.  EDIT: fix post formatting due to forum switchover |
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Quoted: .... However, I do believe, atleast for my person that the XS same-plane aperture is still within the realm of good gains in capabilities/speed for minimal accuracy cost. Besides, I need a high speed rifle to balance out my slow dragging ass. [:)] Wow! Excellent post! Please explain more about the "1/2 oval" milspec A2 rear apertures. For me, the Ashley/XS sights ghost out too much and I find myself losing precision because of it. FWIW I have Ashley/XS same plane rear aps on all my uppers. I'm going to print this out and go measure all of my sight now. I never knew Colt carbines came with 0.052" front sight posts. I swapped a BM carbine's front post out for a BM 0.062" post. I'll try to post back with my impressions. BTW, here's the BM 0.052" and 0.062" posts. (Note that they are not square, meaning only one side can be used. I don't know how to explain it, other than to say that the sides immediately next to the "sighting surface" are angled away from it to prevent glare and give a sharper picture. You lose some elevation adjustment but gain an incredibly sharp front sight picture.) [url]http://www.bushmaster.com/shopping/dcm/9349056cg52.asp[/url] |
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I'll be darned! Colt carbines do have 0.062" posts! Bushmaster carbines come with the standard 0.072". For years I had been satisfied with the stock Colt carbine front sight post. Then I got a BM upper and all of a sudden was shooting much less precise with the irons. After installing the BM 0.062" front sight post, all is good in the world again! (I don't do much shooting with the Colt irons anymore.) If it weren't for this thread, I might have needlessly replaced those Colt posts. The A2 seems to have a thicker outside diameter, particularly on the small aperture (which needs the thickest, IMHO). My A2 large apertures are not countersunk. Both the Ashley/XS and A2 small apertures are countersunk. Now, I'm off to obsess about the rear apertures.... [:)] |
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This is a great post considering Corey and I have been discussing this off and on for several weeks. Some of our discussion has revolved around the benefits of same plane apertures vs. standard A2 apertures, and I'm still not convinced either way. [;)] Usually a .030" increase in aperture size will only increase eye perception error by .000"-.005". For instance, say your group with the A2 was 1.0" @ 50y and 1.5" @ 50y with the XS (mine didn't spread that much!) I need to verify this, but it's my belief that the difference in the size of the XS aperture creates a much larger error than 1MOA. I fully admit that I have limited experience with the large aperture, but [i]in[/i] my limited experience I noticed a spread much closer to 4MOA. Have you verified this 1moa increase in group size at longer range? .5"/124.14 = .004" eye perception error increase. Please correct me if I'm wrong, but I think your math is an indicator of percentage error, not inches of error. This would equate to a 0.4% error. So you are saying that a 13% increase in the rear aperture size creates a [i]real[/i] error of less than 1/2 of 1%? I'm not trying to be argumentative, just trying to get my thought process in line with everyone elses. With my experience that same percentage change in rear aperture size creates a 3% variation in error. Still that's not very much, but it definitely gets more noticeable at longer ranges. Everyone's needs are different, but for my intended purposes I'll take the better low-light and quicker aquisition capabilities over a slight decrease in accuracy. And this is where the main issue is. I agree with you completely that everyone has different needs. For someone taking quick shots in low light the XS may be preferable. But it is [i]my personal opinion[/i] that if you do much shooting with irons at distances farther than a double wide trailer is long, you may want to eek out as much accuracy as possible without greatly reducing your speed in target aquisition. Fast misses are still misses, correct? |
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wyv3rn: You seem really knowledgable re: these issues. Maybe you (or someone else out there) can answer the following questions I have: 1. Describe the "oval" aspect of the A2 apertures as mentioned in your above post. 2. What are the specs (aperture size, same plane or not, etc.) on the A1 and Colt 9mm rear sight apertures? I'm wondering if these could be a viable alternative for same plane apertures. Thanks, Corey |
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Also, FWIW I found the following at Specialized Armament Warehouse ([url]www.sawlesales.com[/url]). SP62816 REAR SIGHT (APERTURE) 9MM $15.00 SP61700 REAR SIGHT (APERTURE) A1 $15.00 SP64524 REAR SIGHT (APERTURE) A2/A3 $12.00 SP61706 FRONT SIGHT POST (A1) - ROUND $6.50 SP64507 FRONT SIGHT POST (SHORT SQUARE - NO TAPER) RIFLE $8.50 SP64665 FRONT SIGHT POST (SHORT TAPERED) CARBINE $8.50 SA02002 FRONT SIGHT POST, ROUND MATCH (.050 IN) $12.00 Oh, and I should also say that yes, I remember the ruckus caused by SAW's owner on this board a while back. So please consider this post as "for research information only." For those looking to derail this thread, please move on. There's nothing to see here.... |
What I mean is the outside shape of the large A2 aperture, not the inner circle. In broad day light I never had any problems, but as I was shooting in more dimly lit areas, my eye would want to center the front sight post slightly more upward from center in the aperture sometimes. The outside shape of the large aperture of the XS is circle shape and my eye centers the front sight post correctly in the large aperture better quickly in varied light conditions. I wouldn't get to caught up in this aspect as it is minor and probably wasn't worth mentioning.
Well, everyone's eyes are different! Go with what works for you! .062" not .052".
I just use a square sight post. My sight picture is sharp. www.ar15.com/forums/topic.html?b=3&f=18&t=181887&page=1 EDIT: fix post formatting due to forum switchover |
I'm sure your eyes are different than mine. I had very little decrease in accuracy at all, around 0-1MOA out to 100y. Even switching from the small aperture to the large aperture normally only widens my groups by a 1-5MOA more and the difference between those is around .130".
No, that math is infact in inches. It is the increased distance that the FSP is out of alignment with the rear aperture.
.004" is infact .4% of 1 inch but we are not talking about increases in percentages of an inch. .004" represents the distance further out of alignment the FSP to rear-aperture was in the example. I don't care what that distance was as a percentage of an inch.
No, your math is erroneous. The increase in aperture size is not 13% from the original. And which size are you talking about? Diameter? Area? Diameter increase = Diameter 1 - Diameter 2 Area=pi*1/2 diameter squared A2 large/small = .200"/.073" XS large/small = .230"/.100" In the case of the large aperture the increase as a percentage of the original A2 aperture is: Diameter: .230"-.200"=.030". .030"/.200"=.15=15% increase in aperture diameter. Area: (.200"/2)*(.200"/2)*3.14=.0314"sq (.230"/2)*(.230"/2)*3.14=.0415"sq .0415"sq-.0314"sq=.0101"sq area growth .0101/.0314=.3217=32.17% increase in area size In the case of the small aperture the increase as a percentage of the original A2 aperture is: Diameter: .100"-.073"=.027" .027"/.073"=.3698=36.98% increase in aperture diameter. Area: (.073"/2)*(.073"/2)*3.14=.004183"sq (.100"/2)*(.100"/2)*3.14=.00785"sq .00785"sq-.004183"sq=.003667"sq area growth .003667/.004183=.8766=87.66% increase in area size
Not taken as such.
I am not going to pretend to understand where the 3% came from or how it relates to the rest of your math above.
Never had that problem with the XS... never heard of anyone elses' accuracy suffering that much either. My groups are pretty much the same between the two apertures, with a SLIGHT decrease in accuracy with the XS. I'm not building a rifle intended for target shooting @ 600y. My rifle is definetly not optimal for that. I'd probably want an elevation adjustable rear sight in which case I wouldn't need a same plane rear aperture anyway. My sights were chosen to fill a certain level of accuracy I deem adequate for my needs and fill a host of other needs/wants I have. EDIT: to fix post formatting due to forum switchover. |
Explained #1 in previous post. I don't really know how wide-spread the effect is person to person but I noticed it in my case. I didn't really notice it until I shot the two apertures one after another, each zeroed in perfect/high light and then taken and shot in low light quickly. Some days my eyes seemed more effected by it than others and even when it did the effect was minor. I probably shouldn't even have mentioned it. 2, no idea, sorry. Thanks for the compliment but, I am new to the AR for sure. I'm positive there are many many people out there who have forgotten more than I know. Oh, and I made a mistake. The A2 large aperture is not countersunk in the direction of the user anyway. EDIT: just to see if it would fix board code b/c of site switchover. What do you know.. it worked. |
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