Barrel Length for a 5.56 SBR?

Discussion about 5.56mm ARs

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FormerNavy
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Re: Barrel Length for a 5.56 SBR?

Post by FormerNavy »

300Blk wrote:You could make a 9mm.
I thought about that but I just have a hard time with how silly an AR looks with a stick mag coming out of the bottom... picky, I know... I just don't understand why a regular AR magazine look-alike can't be made for 9mm like it is for 22LR...
jwb47
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Re: Barrel Length for a 5.56 SBR?

Post by jwb47 »

11.5 inch pre 86 sgw conversion . this bad boy was brutal and would almost make your head explode on full auto . I ended up sticking a 4.5 inch flash hider on it unless I was running my suppresor on it .
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Sharkbite
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Re: Barrel Length for a 5.56 SBR?

Post by Sharkbite »

I built a 10.5" 556 SBR just to mimic my work rifle. The cartridge just loses SO much velocity and effectiveness if you go shorter. I had a 7.5" 556 years ago. What a PITA. Loud, bright, concussive and horribly inefficient

Cheap ammo is the ONLY reason for 99% of guys to do an SBR in that caliber. My 9" blkout is a MUCH better gun in all respects (except ammo cost).
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300Blk
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Re: Barrel Length for a 5.56 SBR?

Post by 300Blk »

The inconvenient truth is that 5.56mm wants a 24 inch barrel and 16 is already a compromise.
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DRYHEAT
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Re: Barrel Length for a 5.56 SBR?

Post by DRYHEAT »

Over the 12+ years I've had an M16, with barrels from 20" (original) down to 6" (Sun Devil/Lothar Walther), all lengths have functioned 100% on FA. I have also had 7.62x39 (11.5"), 9mm (10.5"), and .22 lr (5.5") uppers... but now I am down to just 5.56 and my latest: 8" 300BLK. If they worked in FA, semi should be no problem.
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jwb47
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Re: Barrel Length for a 5.56 SBR?

Post by jwb47 »

300Blk wrote:The inconvenient truth is that 5.56mm wants a 24 inch barrel and 16 is already a compromise.
I agree . I think 20 inches is the sweet spot for a 5.56 ar15. all though I do enjoy my colt 6940 carbine .
Naporter
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Re: Barrel Length for a 5.56 SBR?

Post by Naporter »

I have a 11.5" PSA, but even at that length the velocity loss is ridiculous. Heavier bullets don't lose as much, but factory Fiocchi loaded with 50grn VMaxs come out at a pathetic 2500 fps. Some handloaded 75's got about the same speed following the 300Blk mantra of heavy bullet, fast powder.

I did have some luck with the 50's when I handloaded with H4895. Got up to 2700, but if you're planning on using factory ammo, velocity is going to be a compromise. Going shorter will only make this problem far worse.
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Re: Barrel Length for a 5.56 SBR?

Post by BlogSarge »

I never thought much about buying a 5.56 SBR due to the ballistic loss. But I finally broke down and got a 10.5" Noveske SBR in 5.56. The reason I finally got into a 5.56 SBR is that there are some reasonably effective rounds to be had. For example;

My beloved Federal LE223T3 loads actually do fairly well in an SBR as do the comparable 5.56 FBI load.

Also, Hornady has an SBR-specific round out.. http://www.hornady.com/store/5.56-NATO- ... SBR-Black/ or... http://www.hornadyle.com/products/rifle ... gr-tap-sbr . It uses a 75 gr bullet optimized for the expected velocity of a 10.5 to 11.5 5.56. I just got a supply of it for Test and Evaluation. Once it gets warmer I'll be chronographing it and testing for accuracy.

I'm sure there are other loads out now, but these two are those with which I am most familiar.

Not sure of the maximum range for reliable expansion with either of these, but I don't have any reasonably expected need for my SBR to reach more than 200 yards anyway.

I chose a 10.5 inch barrel because it is long enough to get reasonable performance out of what is now available for ammunition, and short enough to not be too unwieldy with a can on the end. As a side note, and as I believe others have mentioned, a 5.56 SBR is friggin' brutal. You'll want either a can on the end or at least a blast shield type thing.
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A-Game
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Re: Barrel Length for a 5.56 SBR?

Post by A-Game »

16" already is a SBR. 14.5 is a compromise of length and the ability to shoot past 100 yards and still have a M855 bullet yaw. Below 2500 fps it just makes nice small holes.
The M855 bullet was designed around a 20" barrel and M193 designed around a 24".


This look at velocity by the inch and pressure is informative.
http://www.sadefensejournal.com/wp/?p=1093

There is not a better SBR rifle round that I know of anyway than 300 Blk.

I have thought about a 9mm SBR like an Uzi or Sig MPX. I like folding stocks to really make it compact.
Uzi is heavy but feels so nice in hand and is very controllable.

Edit: For non ball ammo choice.
223 is what put DRT on the map.
.39 grain-79 grain bullets to meet personal preferences. They aren't bound to that 2500 fps floor for lethal wound channels that ball ammo has to be subject
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platella
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Re: Barrel Length for a 5.56 SBR?

Post by platella »

I have a BCM 11.5" and my handholds are leaving the barrel at 2700 fps which is fast enough for what I'm doing. Shoots MOA groups. I run it with a suppressor. Installed an adjustable gas block which has softened recoil and my shell casings now drop in neat little piles at 3 o'clock.
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