Barrel Length for a 5.56 SBR?

Discussion about 5.56mm ARs

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xdmalder
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Re: Barrel Length for a 5.56 SBR?

Post by xdmalder »

Could always go with a 458 SOCOM
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A-Game
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Re: Barrel Length for a 5.56 SBR?

Post by A-Game »

xdmalder wrote:Could always go with a 458 SOCOM

You could also throw 2 dollar bills down range at a time instead of quarters and dimes.
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Jim Timber
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Re: Barrel Length for a 5.56 SBR?

Post by Jim Timber »

A-Game wrote:
xdmalder wrote:Could always go with a 458 SOCOM

You could also throw 2 dollar bills down range at a time instead of quarters and dimes.
That's not really accurate though. I just bought a bunch of 300gr Nosler BT's for $.40 bringing my consumables price (assuming 10 firings on brass) to just over $.70 with a premium bullet. Get into some cast or bulk-type FMJ's and it's cheaper yet. My 480gr subs (cast) will end up being cheaper than a factory 300BLK in any flavor you can come up with.

Image

Is it as cheap as 300BLK? Of course not - it's 2x the volume and weight for powder and lead per shot. But it's not $2 a hole either.

Having primarily dealt with .458S for the past 3 weeks, I was dealing with 300BLK cases the other day and just laughed at how tiny they seem now.
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19dsniper
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Re: Barrel Length for a 5.56 SBR?

Post by 19dsniper »

I was in the same boat as the OP. I started by building a 10.5" Mk18 clone for my wife. While this upper has always been extremely reliable, I've never had a hiccup with it, I wanted something a little longer for myself. I only wanted longer because of my shooting style/stance. I am one of those guys that likes to hold farther out on the hand guard. A magazine well is not the correct position for your support hand! Anyways, on my last 5.56 upper i went with a 11.5 inch BCM barrel. It too has been 100% reliable. I do like a short 5.56 and yes, i understand that it is a compromise sometimes. It depends on what you plan on doing with it. For me, its a short truck gun that can be concealed easily. Yes, i also have a number of 300 BLK rifles and do prefer the ballistics, But sometimes i still like the 5.56 especially on trips where the other people I'm working/traveling with are carrying 5.56 guns. Im also that guy that if I'm on an extended trip/assignment, will find out what caliber everyone else is carrying so that i can carry the same for ammo/mag compatibility. Lets face it, this doesn't apply to everyone, but if you have access to enough weapons to do that, and your comfortable with it, why not.

Back to the barrel length and part wear and tear. On my uppers, well all of them actually, i run the Trifecta brake. My M24 is the only rifle i actually run the saker flash hider on instead of the brake, and thats only because thats what i had.
Using the brake, even though its ungodly loud when unsuppressed, acts as a sacrificial baffle when running suppressed. This will knock down a lot of that wear and tear your talking about. Alot of newer suppressors don't even require them, but its still a good idea in my opinion, to run one anyways. My SilencerCo Saker for example is made of Stellite (30% stronger than Inconel). Its actually Full auto rated down to 7". Yes, its a heavy beast, but its built like a tank. I still run the brakes anyways.
The 10.5 was so brutal at first with the MB attached that i bought a FH instead. It definitely helped tame some of that concussion, but in the end, i opted for the brake instead as with a barrel that short, i don't plan on running it unsuppressed and the brake will act as a sacrificial blast baffle.

As far as length. That depends on you and what you plan on doing with it and how you set it up. On both of my uppers I am running Syrac Ordnance Gen II adjustable gas blocks. I adjust it to fully function with my weakest handholds, unsuppressed. This allows me to run any ammo thru my rifle wether suppressed or not. Yes, on my really hot loads, with the suppressor, it may be a little overpassed, but thats not an issue. I would always rather be overpassed than under gassed. It is not overpassed in a bad way, you can only tell by looking at the ejection pattern.

Something else to look at if your running DI without an adjustable gas block is dwell time. An 11.5" will give you approximately 40% more dwell time. What that means is that it is more forgiving and doesn't beat up your parts as much. There is also a difference in recoil. I can only tell the difference with Hot duty loads and when I'm actually trying to discern any little differences. But it is there.
I read awhile back about some very crazy velocity swings between the 10.5 and 11.5 barrels, and i have to say that I'm not a believer in what i read. I have compared the same load from both uppers before. Yes, there is a difference, but nowhere near what i have seen listed by some others. I plan on retesting once i get my new Magnetospeed V3 delivered.

On to what someone else brought up about lethality range. It depends on what you want to run for ammo. IF i had to run mil spec ammo in an SBR i would personally take M193 over M855. M193 should be running about 2,700 fps out of the 10.5" which is right on the verge of its fragmentation threshold. To each their own. But the M193 should still give decent results out to about 50 yards or so. YES, it will kill much further than that, but so will .22LR. What is meant by this is that the M193 should still reliably fragment out to 50 yards or so, but after that it will still act like a standard FMJ.

HOWEVER..... This is not the ammo i use for these rifles, and neither is it what you should use either for social work. Range/training time, absolutely. Its very reliable ammo But for defensive work, please pick something else. Im not going to tell you what to use. You will have to do your own research on that one.
For me, I use a 62 grain Bonded Spire Point (Federal Fusion projectile) at 2,602 FPS. I hand load this ammo fairly warm, but to me accuracy is more important than velocity. Even at my slightly slower than Max velocity, this projectile will still expand out beyond 300 yards with my 11.5" (if you go off of the expansion threshold that was given to me by Federal, or 550 yards if you go off of the expansion threshold given to my agency, Go figure!) Personally, i believe its threshold is actually somewhere between the two. I have seen excellent expansion at an impact velocity of less than 1,700. which would actually come close to the 550 clam in a longer barrel.)

OR: i load a 55 grain Hornady Spire point at 2,754 FPS (same velocity as LC M193 from this barrel) with 25.4 grains of TAC and get expansion out to 290 yards. Well, what happens at 300 yards and beyond? It acts just like M193 and doesn't expand, still giving you a .22 cal hole in one side and possibly out the other. This is all from a rifle that i never plan on using past 200 yards. Will it work past that, sure. But again, it all depends on what you want to do with it. For me, reliable expansion from a short rifle at either 290 or 550 yards? I will take it!
emmagee1917
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Re: Barrel Length for a 5.56 SBR?

Post by emmagee1917 »

xdmalder wrote:Could always go with a 458 SOCOM
The problem right now , as in today , is the 1 in 14 twist barrels will not stabilize a 400-500 grain bullet in a short ( sub 16 inch ) barrel reliably .
Tromix is coming out with 1 in 10 twist barrels right now , should be ready soon . A suppressed 8 inch throwing a 500 grain at 1,000 should cure whatever is ailing you .
Chris

PS ,
I should note that my 8-inch is accurate for what it is . I'm meaning totally stable out the muzzle , i.e. , no baffle strikes .
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