300 blackout SBR - does a free floated barrel matter?

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DarthNul

New member
I'm in the planning stages of building a 300 blackout SBR with a 10.5 inch heavy profile barrel. No way of knowing how many more months it'll be for the tax stamp so the planning stage may be prolonged... :rolleyes:

All my other AR-15 rifles (16,18, and 20 inch) have free floated barrels to improve accuracy, but given the rigidity of a short/heavy barrel and the limited range of the round, is there any measurable benefit?

My choices of hand-guards will certainly be influenced by whether I free-float or not. I'm hoping to find a hand-guard to be as long (and wide) enough to cover an adjustable gas block, but leave the Sig QD suppressor mount accessible.
 
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marine6680

New member
Free floating does a couple things... But they don't really "improve" accuracy though.

One thing they do, is isolate the barrel from outside influence/pressure on the handguard. Because its not really possible for a person holding a rifle to always hold it exactly the same way with the forces distributed the same way... a non-free float barrel can have slight changes to the barrel harmonics from shot to shot. This opens up groups, and typically becomes more noticeable at ranges of 200+ yards, though a good shooter could tell the difference at closer ranges. By that token... If the same rifle was secured in a shooting rest, then it wouldn't make much difference between free float or not.

Another thing free floating does, is isolate the barrel from difference in heat expansion. As a barrel heats, it expands and this affects barrel harmonics. On a non free float barrel, the differences in expansion between the barrel and the other parts it may be in contact with, will create added pressure which will increase the shift in point of impact due to heating. This effect can be significant at 100yds+ depending on the individual rifle. It can be noticeable at shorter ranges, (usually after rapid fire and a very hot barrel) but typically isn't an issue for making center of mass shots. If you need to take a more precise shot, then it may throw you off, but such need is not likely in the types of use an SBR is for.


So, seeing as an SBR is usually looked at as a CQB type of rifle, with ranges of 100yds and less... you do not really need a free float barrel. But there is no reason not to either other than cost.
 
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rickyrick

New member
If you have a pistol length gas system, free floating will be the only practical choice, even carbine for some
 
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marine6680

New member
Yeah... They are right about the shorter gas system.

But I would imagine it being a carbine length for an actual SBR with a 10.5in barrel length, but I don't do 300blk, so optimum gas system length for that caliber is not my strong point.

I usually see pistol length gas systems only on barrels of 7in or so.


If you like long rails, or to reach out on the handguard farther when shooting... Free float is the only way to effectively get an extended reach on a barrel with shorter gas system.

I would get a hand stop though, if running a long rail on a short barrel. One slip and you may end up with a holy hand.
 
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Sharkbite

New member
300BLK SBR's should be pistol gassed. Anything else WILL make it harder to get the rifle to function with subs.

Look at the way AAC ( the ones that brought the concept to market) sets up its guns. I have a AAC 9" SBR and its FLAWLESS in its function
 
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TMD

New member
When it comes to the .300bo the only gas system I've ever seen on barrels shorter than 16" is pistol length. Not saying there isn't any carbine length gas port sbr's out there in this caliber but in the 6 years I've been playing with it I haven't seen one.
With that being said only hand guard option will be free float. Also a low profile gas block will fit under most hand guards as well
 
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marine6680

New member
I think I remember people talking about 300blk SBR and pistols saying that carbine is fine if you never run subsonic ammo.

But it sounds like pistol length is the way to go for overall function and reliability.


So while there is no need ballistically, for usability free float is the way to go.


Be sure to show us how it looks when it's built. You can always build it as a pistol until the stamp comes in.
 
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