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zukiphile
September 15, 2012, 07:44 AM
Why is an AR front sight located on the gas block rather than the end of the barrel?

I can't see how reduced sight radius is a benefit, yet the ordinary AR design, much like a galil or valmet uses a shorter radius than would be easily obtained by locating the fronts sight out at the end of the barrel.

There must be a reason for this. Could anyone with a spare moment educate me on this?

Mobuck
September 15, 2012, 07:16 PM
Conservation of material and maintaining light weight. Original concept was increasing volume of fire w/o increasing weight of ammo load. Short range accuracy was adequate with the short sight radius. Long range open sight shooters use an extension to increase space between front and rear.

madcratebuilder
September 16, 2012, 06:50 AM
There are builds that have the gas block under the hand guard and a non functioning FSB near the end of the barrel.

My last build was similar, gas block under the guard and a LMT front sight on the extended length hand guard. I was trying to work with parts I had laying around and this is what came together.

http://i32.photobucket.com/albums/d37/madcratebuilder/AR15/july12build01.jpg

Justice06RR
September 17, 2012, 12:02 AM
The AR sight radius is plenty long enough for the rifles' intended use. Remember that there are different types of AR's: Rifle, Midlength, and Carbine, which have different length sight radius.

Furthermore you can always change the sight radius by changing your sights i.e. with a longer rail.

One last thing, you know that an AR15 is not really a sniper rifle right? Its more of your generic battle rifle that can fill many roles

LSnSC
September 17, 2012, 06:00 AM
I see some of the guys shooting irons at 3 gun matches with the sight mounted right behind the compensator to get a longer sight radius.

zukiphile
September 17, 2012, 08:49 AM
Conservation of material and maintaining light weight.

I find that rationale completely plausible in a "good enough" for government way. Yet, more sight radius (within reason) will be always be better, and increasing it seems like a low cost improvement for any barrel length.

My last build was similar, gas block under the guard and a LMT front sight on the extended length hand guard. I was trying to work with parts I had laying around and this is what came together.


I admire that kind of frugality. It was frugality in part that prompted my question. There are some very pricey FSBs that don't look all that sturdy, while the ordinary front sight moved out to the end of the barrel should do just about as well.

However, I take it that mounting the regular FSB at the end of a barrel can be tricky and take a skill or two.

I see some of the guys shooting irons at 3 gun matches with the sight mounted right behind the compensator to get a longer sight radius.

Does anyone offer this in an upper with a 20 inch barrel? Or is there an easy way for someone with very modest mechanical skills to do this?


This may read like a lot of very stupid questions, so if there is a resource I should be consulting, please feel free to direct me.

Thanks in advance.

LSnSC
September 17, 2012, 10:53 AM
Replace the gas block and get a clamp on A-2 sight to mount behind comp/ flash supressor. Armalite makes a good clamp on A-2 sight that is popular for this application.

There are some clamp on globe style target sights available as well.

Noveski Offers a Tac Irons upper, and they are the only ones I am aware of.

Im not sure its worth the effort unless you are a competitive shooter, even then , the service rifle shooters seem to be doing very well with the front sight right where it is.

FWIW, I bought a PRI Same plane gas glock for my AR-10 flat top and added a fixed Troy clamp on front sight and DPMS "shorty" A-2 rear. This setup is serving me well. I had no problem hitting steel flashers out to 300 yds at 3 gun match yesterday.

zukiphile
September 17, 2012, 02:09 PM
Thanks for the practical advice. The Armalite FSB looks versatile.

Have you ever used the aperture front sight post?

EDIT - The Levang aperture gets poor reviews, but they don't seem the only ones with the same idea.

chadio
September 17, 2012, 02:22 PM
My front sight is mounted as far forward as possible on the barrel (not the gas block, or the rail, etc.), my rear sight is mounted as far rearward as possible on the receiver. The rifle has a 16" barrel wit a 20.75" sight radius. It may look a bit strange, but it works better for me (especially with the 0.050 front sight post)

LSnSC
September 17, 2012, 06:19 PM
I use a .045 National Match post I bought from White Oak Armaments.

Sinlessorrow
September 17, 2012, 07:02 PM
You are over thinking this, I have no issues hitting 300M targets using a standard M4.

Palmetto-Pride
September 17, 2012, 07:27 PM
Why is an AR front sight located on the gas block rather than the end of the barrel?

I have know idea if this is one of the reasons, but what about the mounting of the bayonet could that be one reason for the FSB being the way it is.

http://www.quarterbore.net/forums/photopost/data/529/medium/M4Bayonet.jpg

chadio
September 18, 2012, 06:04 AM
You are over thinking this, I have no issues hitting 300M targets using a standard M4.

Good for you - however, this thread is not about how good of a shooter you are, it is about sight radius of the AR;)

zukiphile
September 18, 2012, 01:17 PM
http://puuloa.com/Kevin%20Pictures%20Movies/nramtch.jpg

This illustrates an exaggerated application of the idea.