Diminishing returns for sight radius

J

johnwilliamson062

Moderator
Thread on velocity got me thinking...

Using AR barrel length, not sight radius length, I know
So, 16 to 18 is a big leap.
16 to 20 is also pretty helpful.
20 to 22?
22 to 24?

I don't think there are many AR options for greater than 24, but what about it?
Just say to hell with it and use optics?
 
No matter the barrel length, you will be hard pressed to find a gas system length greater than the "rifle length." This is standard on 20" barrels. Since the sight radius is based off the gas block, you will not find one longer than that which is usually on a standard 20" barrel unless you find some off specialty thing that I've never seen.

So... to answer your question... beyond 20" is diminishing returns short of something exotic that isn't common, and then it will be expensive. It could be argued that a carbine length sight radius is almost as good as a rifle length, so diminishing returns can be found at the carbine length gas system. I know I can shoot a carbine length rifle as accurately as a rifle lengthed one, and don't really notice the sight radius difference. While this is subjective, I can say with authority a 20" barrel is your definite, without question, pretty much going to be the point of diminishing returns.
 
I built an AR early this year, and I used a Green Mountain 26" match barrel. And optics, because unless you get extended sights on your barrel, your front sight will live about where your gas block is, or about 13" on a rifle-length system, giving you a sight radius of about 20"
 
I don't think there are many AR options for greater than 24, but what about it?
Just say to hell with it and use optics?
Click to expand...

There a few, not so much in 5.56 or even AR-15, more like AR-10. Pretty much all the ones I have seen have optics on them as they are designed to be long range shooters.
 
A lot of "space guns" in High Power use a low profile gas block and a normal competition front sight hood with swappable inserts. Compared to the folks using AR-15s in service rifle configuration, it does make sighting easier.

Jimro
 
You don't have to have a longer barrel to get a longer sight radius. I have seen a few "bloop tubes" on AR based match rifles.
 
I made myself an iron-sighted play-thing a few years ago on an AR platform.
I took a 28 inch blank, 1-8 twist, and turned it to standard rifle contour from the gas journal to the breach. I then turned the barrel from the gas journal to a point 3" behind the muzzle at .680" From the point of the .680" diameter 3" behind the muzzle I then jumped back up to .750, and lastly I turned a stub 1/2" diameter and threaded it for 1/2X28 threads.

I mounted a low profile gas manifold on the barrel at the standard position for a 20" rifle and then mounted a GI front sight tower on the barrel up at the front just .050" behind the flash hider. I installed a hoop with a cross hair for the front sight itself, and I am using a standard GI detachable rear carry handle.

I made my own free float tube that come all the way out to the front sight tower. It would work just as well with a standard rifle length FF tube, but I like the way mine looks better. (It looked better before the pint got chipped off, but that's what happens when you carry them around a lot and get in and out of trucks with them all the time.)

This rifle upper has a 33-1/2" sight radius. That combined with the cross-hair front sight makes for a very good play thing. I will not say it makes me the marksman I was in my 30 or even my late 40s, but I can hit very small targets at 300, 400 and 500 yards with this upper.

Form a rest I hit 6 out of 6 chicken eggs with this rig at 240 yards.
Makes me feel a bit younger when I do that.

 
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I know I can shoot a carbine length rifle as accurately as a rifle lengthed one, and don't really notice the sight radius difference.
Click to expand...
It is hard to firmly attribute differences in accuracy to any single characteristic between one rifle and another, but I see very few competing with 16" rifles, even at 100 yards, and I personally find the 20" very advantageous.
 
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