Baffled by AR front sight placement


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ChristopherG
March 19, 2010, 12:33 AM
Why don't AR manufacturers, or customizers, or anyone I can basically find, put the front sight of the rifle as close as they can to the end of the barrel? I know iron sights are a very secondary deal for a lot of--I should think most of--AR users. But surely not all.

My issued patrol rifle is a 16" A2 M4gery. I'm happy to have it, but my department only allows iron sights, and the sight radius on this thing is ridiculously short compared to what it should be. I want to replace the upper (which they will allow) with a quality midlength that's free-floated, and I'm trying to figure out if there's some reason the front sight shouldn't be out there at the end of the gun where god intended it, and if it should be, how to get it stuck on there.

Anyone have any experience or knowledge in this area? Or is there some reason I haven't discerned for these artificially stumpy sight radii?

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Oic0
March 19, 2010, 12:38 AM
I'm eager to learn that one myself. Purposely shortening the sight radius seems counterintuitive.

briansmithwins
March 19, 2010, 12:41 AM
Because the front sight base (FSB) is also the gas block. For reliable functioning you need about 4" of barrel past the gas port.

2 choices: 1) Get a 'dissipater' style upper that has a FSB near the end of the barrel and a gas block under the handguards. 2) Educate your department's trainers and get optics on those rifles.

CMMG has some listed on this page: http://cmmginc.secure-mall.com/shop/index.php?shop=1&cat=94

The one you want is the 'CMMG 16 inch M10M MedCon Rifle. Mid-length gas system hidden underneath a rifle length handguard, rifle length sight radius.'





BSW

M1key
March 19, 2010, 12:41 AM
Gas block was probably a convenient place to put the sight, I guess. Has worked fine for me all these years. Rock River makes a nice middie. Or how about a Dissipator upper?

lysol
March 19, 2010, 12:51 AM
shorter site distance equals faster target aquisition?

M1key
March 19, 2010, 01:38 AM
Maybe. Faster gas cycle for sure.

Zak Smith
March 19, 2010, 01:39 AM
Why don't AR manufacturers, or customizers, or anyone I can basically find,
Sure they do, just not very many. In Service Rifle, you can't change the external appearance of the rifle, so a modified setup it out. In 3-Gun, you will find some competitors using extended front sights in Limited division. JP Enterprises has built some of these. In other long-range competitions, the AR-15 is not a competitive platform.

Double Naught Spy
March 19, 2010, 09:22 AM
shorter site distance equals faster target aquisition?

Which also means faster target loss. A shorter sight radius might be fine or faster at CQB ranges, but also means being more difficult to use for longer ranges.

As such, I would be willing to guess that the shorter sight radius wasn't done for targeting purposes.

Taurus 617 CCW
March 19, 2010, 09:57 AM
Putting a sight all the way at the front of the barrel can mess with the barrel harmonics (just a theory). The model we build is essentially a dissipator type, mid length gas system, with a flip down ARMS front sight gas block. It looks longer than it really is (14.5" barrel). Link to photo for illustration: http://www.nextgenerationarms.com/

I really can't understand why anyone would want to shorten their sight radius either. We use a Trijicon reflex sight for rapid target acquisition.

ChristopherG
March 19, 2010, 11:03 AM
shorter site distance equals faster target aquisition?

Nope, I'm pretty sure that's not true.

Like Zak, my mind turns to the choices that competitors make to understand what works--'cause they've tried everything and found out on the clock and under stress. The guys who win 3-gun limited at top levels are using long guns with sights attached way out at the end of the barrel--or at least a full rifle-length sight radius.

I understand the mechanics of why the sight corresponds with the gas block; but obviously that's a design element that we have the technology to overcome. For instance, the CMMG models that BSW helpfully points out, and which I've looked at before. The only real difference between that and what I have in mind is a free-float tube to easily attach a white light (and anything else I should wish down the road).

I know JP makes a clamp-on sight base that can attach to a barrel of various dimensions and at any point along its length. I guess I'm just a bit puzzled by the relative lack of options to make real maximum use of iron sights on the AR platform. There are a few out there, but not many.

As far as trying to talk my department into a change, we've had that conversation more than once, and all I know at this point is it's not changing anytime soon. I'll keep pushing for it down the road, but in the meantime I want to be carrying the best setup I can. I'd also like to play some 3-gun with it (limited division for now, of course).

I suppose my ideal setup right now would be a BCM stainless 16" midlength with a 12" PRI tube or a troy TRX tube--like this:

http://www.bravocompanyusa.com/PhotoGallery.asp?ProductCode=BCM-URG-MID16+SS410+PRI12+IBBK

--but with a sight placed on the exposed end of the barrel. Maximum room for hand placement and accessory placement, maximum sight radius. And if I wanted to go with an optic on the same gun down the road, a sight 4 or 6 inches farther away is going to be less of a potential issue.

Zak Smith
March 19, 2010, 03:17 PM
I know JP makes a clamp-on sight base that can attach to a barrel of various dimensions and at any point along its length. I guess I'm just a bit puzzled by the relative lack of options to make real maximum use of iron sights on the AR platform. There are a few out there, but not many.

Well, I think the main reasons are that the sight radius on a 20" is still pretty good and the AR-15 has very good iron sights anyway. Stock M16A2/AR-15A2 sights are sufficient to hit a 12x12 or 12x18 target at 400 yards using a normal battle zero.

amd6547
March 19, 2010, 04:13 PM
Remember, the original AR was intended to also fire rifle grenades in the pre-M203 days...that is the reason for the length of exposed barrel in front of the sight.

ChristopherG
March 19, 2010, 04:28 PM
Well, I think the main reasons are that the sight radius on a 20" is still pretty good and the AR-15 has very good iron sights anyway. Stock M16A2/AR-15A2 sights are sufficient to hit a 12x12 or 12x18 target at 400 yards using a normal battle zero.

Right; I guess I should specify on shorter guns, particularly carbine length gas guns. But amd6547 is right to note that the military had uses for that exposed barrel length that I don't. That is probably a key part of the puzzle that I had totally neglected.

WNC Seabee
March 19, 2010, 04:41 PM
Bayonet mounting comes to mind. Although I've never seen the real value in having one mounted outside of the .mil. I doubt it would look all that great for LEO to start mounting bayonet charges....

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