View Full Version : anybody have a good barrel length/velocity table for 556?
I'm having a very hypothetical debate with myself about what barrel length to go for on my next carbine. I just sold my only AR (16" cav/cmmg middy) :mad:
been shooting my glocks a fair amount... and i've always had a fascination with short rifles. so i'm thinking now that i live in the wonderful free state of colorado, i may build up an SBR sometime in the next year or so.
basically longer is better for ARs as far as velocity and function go... so would a 12.5 be a good compromise? the 10.5's are cool, but what's the muzzle velocity? are they reliable?
i probably will not be running a can any time in the near future.
I would say if you are going to do a SBR build, 10.5 or 11.5 would be a good selection for upper. I like the 12.5 because it will be able to fit my AAC Spr/m4 (and Noveske doesn't make a 11.5" bbl). I don't have any ballistic charts or tables but if this rifle is going to be used as a paper puncher get as short as you like, if it's for a SHTF/Self defense gun, go with the 10.5 or 11.5 as stated above. Anything longer kinda makes the process of NFA stuff not really worth it. You could also look into 6.8spc, that caliber is pretty good for keeping decent velocity from short bbls. It really depends on ammo as well, keep in mind this is my opinion and I don't have any actual facts to base this on, just my observations. Best of luck.
decodeddiesel
10-01-09, 12:10
A lot of people seem to like the 12.5" uppers, but I personally prefer 11.5" (Colt, BCM), 10.5" (LMT, Noveske, Sabre), or 10.3" (Daniel Defense, Colt). For me if I'm paying a $200 stamp I want something to be as short as possible. The qualifier to that statement though is it must still reliably function and maintain enough muzzle velocity to achieve the desired effects on the target (ie fragmentation) at the prescribed ranges an SBR is designed to be used at. The nice thing about the 10.5/10.3 is that since it is a standard issued barrel length for US forces it has been very carefully characterized and tested for function.
77 grain bullets still the hot setup for the short guns?
DocHolliday01
10-04-09, 21:31
Im planning on trying the 70gr. Barnes TSX load that SSA offers out of my 10.5.
decodeddiesel
10-04-09, 21:45
77 grain bullets still the hot setup for the short guns?
Hornady 75gr 5.56 TAP is probably best.
Just a little side note. I built my SBR using a BCM 11.5" upper. It has Magpul front and rear sights. markm and myself went out the other day shooting again and I was easily able to hit a steel silhouette at approx. 220 yds. using both 55 and 62gr. ammo. I always get amused when I hear people say that shorties can't hit past xxxx distance. In the near future I may put my Leupold or ACOG on there and try some 300 yd stuff.
My 14 year old was pinging away at the steel hanger set up at 100 once he found his niche.
Page down a bit on this post. I have a barrel velocity chart listed there.
http://m4carbine.net/showthread.php?t=38754
Here is another from Wes at MSTN with 77gr.
http://www.ar15.com/forums/topic.html?b=2&f=134&t=149575
Just a little side note. I built my SBR using a BCM 11.5" upper. It has Magpul front and rear sights. markm and myself went out the other day shooting again and I was easily able to hit a steel silhouette at approx. 220 yds. using both 55 and 62gr. ammo. I always get amused when I hear people say that shorties can't hit past xxxx distance. In the near future I may put my Leupold or ACOG on there and try some 300 yd stuff.
My 14 year old was pinging away at the steel hanger set up at 100 once he found his niche.
I'm guessing most of the people who make claims about the "limited" external ballistics of SBRs have never actually tried it. I have a 10.5" LMT that can make well-centered hits all day long on 200 yard steel with both XM193 and 75 gr. Hornady (the latter making VERY well centered hits) using an Aimpoint Micro or irons. It actually shoots better than my 16" Colt. It's 80%+ on the 300 yard plate, and the misses are probably my eyesight and not the gun. The plates are about 12x18 inches, the 300 is a bit bigger.
Stan_TheGunNut
10-09-09, 23:34
I'm guessing most of the people who make claims about the "limited" external ballistics of SBRs have never actually tried it. I have a 10.5" LMT that can make well-centered hits all day long on 200 yard steel with both XM193 and 75 gr. Hornady (the latter making VERY well centered hits) using an Aimpoint Micro or irons. It actually shoots better than my 16" Colt. It's 80%+ on the 300 yard plate, and the misses are probably my eyesight and not the gun. The plates are about 12x18 inches, the 300 is a bit bigger.
People are not saying that you can't hit something at 200-300 meters with a 10.5" SBR. They're saying the bullets fragmentation (thus terminal ballistics and wounding potential) will be virtually non-existant at that range with a 10.5" barrel due to the loss of velocity. This is different than just punching holes in paper or making steel clang.
Regarding the OP's original question...I think a 12ish inch SBR is a good compromise. Still short, but better terminal performance. I personally have a 10.5" SBR in 5.56mm. It's completely reliable with everything I"ve put through it, both with and without silencer attached. I've put ~600 rounds through it, everything from Wolf to Hornady 5.56 TAP. No issues at all so far.
http://www.ttellc.net/misc/velocity.jpg
A friend of mine, TimP, was clanging the 472yd steel with his 10.5 LMT in New Mexico back in Nov, 2007 with a Meopta K-dot @ 4x. So I know it can be done if you know your weapon.
No I have actually heard people say that you can't hit targets at that distance.
I wouldn't want to take that bet about the wounding potential.
People are not saying that you can't hit something at 200-300 meters with a 10.5" SBR. They're saying the bullets fragmentation (thus terminal ballistics and wounding potential) will be virtually non-existant at that range with a 10.5" barrel due to the loss of velocity. This is different than just punching holes in paper or making steel clang.
Regarding the OP's original question...I think a 12ish inch SBR is a good compromise. Still short, but better terminal performance. I personally have a 10.5" SBR in 5.56mm. It's completely reliable with everything I"ve put through it, both with and without silencer attached. I've put ~600 rounds through it, everything from Wolf to Hornady 5.56 TAP. No issues at all so far.
People are not saying that you can't hit something at 200-300 meters with a 10.5" SBR. They're saying the bullets fragmentation (thus terminal ballistics and wounding potential) will be virtually non-existant at that range with a 10.5" barrel due to the loss of velocity. This is different than just punching holes in paper or making steel clang.
Yes, I know that. Terminal effect is not what I am referring to. As Iraqgunz said above, many people do believe that shorter barrels lack "accuracy" or external ballistics to hit targets at 200+ meters.
Eric Torres
11-15-09, 02:52
I am currently on deployment. The only two guys in my platoon that go out with anything longer than 10.5" MK-18s are the snipers. (Mine has the new DD MK-18 FF rails, and a Noveske barrel. Yes I'm "cheating to defeat the enemy" Thanks JOHN). It is mission specific and my unit is doing urban and suburban DA. It does and is doing the job every day, or should I say night. The 77gr ammo helps, and my rifle shoots sub MOA.
It may not be "optimal" but the 10.5s are no shit doing the job. Not theory, range, or third hand, but doing it right now....tonight.
Hope you are all doing great. Other than missing my little ones, I'm having a good time.
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