16" Ar-15 range limitations


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high country
June 15, 2010, 05:50 PM
I am considering uppers for an AR build, and my question is this: How limited is a 16" barrel on longer range shots (say 500 yards)? With all else being equal - same quality ammo, 1/7 twist crome lined barrels, use of optics so sight radius is out of the equation, shot from a bench, etc.

I am leaning towards a mid length 16" upper, but I don't want to limit myself if I want to take the occasional long shot at paper. My understanding is that the real differences here is the lower muzzle velocity of the shorter barrel, which means the bullet goes sub-sonic faster, and the bullet will be more susceptable to wind drift. How much practical effect of this will be discernable at 300, 400, 500 yards as between the two barrel lengths with the same ammo? How many people here take shots like that with a 16" rifle?

I would like the smaller package offered by the 16" barrel, but I don't want to be unhappy with my descision in the mean time because of range limitations.

Thanks in advance for any thoughts:D

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speaksoftly
June 15, 2010, 05:53 PM
I would imagine the "limit" with a 16 in barrel would be a bit further. Take a look at the link.

http://www.youtube.com/watch?v=eJV0qRsvwW4

brian923
June 15, 2010, 06:14 PM
You lose about 50 fps per inch from 20 " barrel if I remember correctly.
I went middle of the road and got a white oak armament 18" spr barrel in 1/7 twist. I think that for paper shooting, 16" is good, but you might want to get a thicker stiffer barrel to give you an edge in the accuracy department. But that may contradict the reason for you wanting the smaller rig. I always tell people that the best thing to do when building an AR, is to purpose build it. If you want a close quater rig, build a lite fast handling rig. If you want a DMR, build a heavy long barreled upper with the best components. As for a good handling rifle that will reach out once in a while, I would suggest at the least, a good reputable barrel, free float tube and a good trigger.
I am not a profesonal builder, but I know this will work. Hope this helps, brian.

taliv
June 15, 2010, 07:00 PM
variable, but the lighter your bullets, the worse it will be. if you're planning on shooting 75 or 77g, it will be manageable but you'll have to be a little more attentive to the wind. if you're shooting 55g, you will prob want a full sized target :)

benEzra
June 15, 2010, 09:41 PM
My understanding is that the real differences here is the lower muzzle velocity of the shorter barrel, which means the bullet goes sub-sonic faster, and the bullet will be more susceptable to wind drift.
If you're worried about the bullet slowing to the transonic range by 500 yards, iSnipe is showing even a 55gr JHP comfortably supersonic at that range. The speed of sound at sea level under standard conditions is 1,116.4 ft/s (varying somewhat with temperature and conditions), and I'm showing a 55gr bullet with a ballistic coefficient of 0.243 still going ~1360 ft/sec at 500 yards, assuming a muzzle velocity of 3000 ft/sec. The heavy 75- to 77-grain bullets will probably be your best bet, though.

gb0399
June 15, 2010, 10:21 PM
From my own experience I can tell you that with an M4A1 with 14.5-15 (not sure of exact lenth) inches of actual barrel, standard handguards, ACOG 4x, shooting 62gr bullets you can hit an "iron maiden" out to 600 meters. I'm sure that some of you can probably do it further than I.

W.E.G.
June 15, 2010, 11:14 PM
The military qualifies on 500 yard targets with a 14.7" barrel.

I wouldn't worry about it if I were you.

The .223 from a short barrel still has plenty of gas to hit paper at 500 yards.

Hatterasguy
June 15, 2010, 11:16 PM
I'd say 500-600 yards if you can hit what your trying to hit at that range.

The round will do the job if you put it on target.

MTMilitiaman
June 16, 2010, 01:13 AM
It depends what your definition of "effective" is.

If you're only interested in how far away you can reliably hit a target, 500 yards is doable. Hell with an ACOG, it's almost easy. However, no one will ever convince me the 5.56mm is a 500 yard fighting cartridge from any rifle with any ammunition, and it doesn't matter what optic or high tech gizmo you have on there. The standard 62 gr ball load is hovering around 1600 to 1800 fps at that range--it's been out of it's reliable fragmentation range for 350 yards and is now far enough below the 2000 fps barrier that even so-called hydrostatic shock is a non-issue. It has the same energy as the 9mm, with half the mass and frontal area. So if by "effective range" you want to know how far away you can be effective, then I would say the M4 is marginally shorter in this regard than the M16, but not by much. I would give both of them about what I would give any other poodle shooter, 250 to 300 yards depending on ammunition type, optics, and barrel length. If you are under the impression that because only hits count, all hits count, then the M4 could get you 500 yards, albeit with anemic enough ballistics that I wouldn't expect reliable stops on coyotes with it at that range.

high country
June 16, 2010, 01:30 AM
Thanks for the comments. Sounds like my desire to be able to shoot out at 500 yards is not out of the realm of reason for a 16" barrel, or even outside the range of normal use.

And, from what I have read, at that range, the 20" barrel would be much better off using heavier bullets too. I guess what I take from that is that the step from 1/9 to 1/7 twist to stabilize heavier bullets is arguably more relevant than the extra 4" of barrel?

Taliv - I grew up in Oak Ridge. Beautiful place. I hope to end up back in that area at some point. Good to see that there is an active shooting community there.

Edit - I am speaking strictly of shooting paper/steel/gallon jugs of colored water at 500 yards for practice, and didn't intend to start a terminal ballistic effectiveness debate. For the purposes of this discussion, when I say effective, I mean sufficiently precise to make a .22 hole in an inanimate object at that range. Perhaps a misuse of the term "effective, and certainly terminal ballistic effectiveness at least as important, and should be taken into account, but is a seperate discussion.

Tirod
June 16, 2010, 09:10 AM
If it's any help, the SDM uses a 20" 5.56 to reach out to 500m, and further. The inclusion of the rifle in the squad was to offer that range organically with a weapon that didn't appear capable, unlike the M14.

The Army certainly does intend to exploit the term "effective" in that application.

Kwanger
June 16, 2010, 12:14 PM
High Country - you got it on your second post - as well as twist rate for the heavier bullets, I'd say there are a lot more factors more important accuracy wise than 4 inches of barrel - ammo quality, scope, etc.

desidog
June 16, 2010, 12:25 PM
I'd say the variables of bullet weight and barrel twist are just as important as bbl length.
Also, there's a difference between shooting at paper and shooting at fur at that range.

Bartholomew Roberts
June 16, 2010, 02:07 PM
I've shot a 16" Bushmaster HBAR at 600yds at the L. T. Dillon range using Federal XM193 55gr... groups were about 36" all together; but probably closer to 18" once I got the wind down. The 55gr was still supersonic at 600yds, though my ballistics calculator shows that distance is pushing it for 55gr.

The biggest issue at that distance is the wind.

Justin
June 16, 2010, 03:03 PM
I've hit steel IPSC C-zone targets at 500 yards with a 16 inch gun and an ACOG. It's doable.

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