Best SBR AR-15 BBL Length

For 5.56 I wouldn't go shorter than 10.5". Personally if I'm going to the effort of making an SBR I wouldn't consider anything longer than 12.5". I think there are some compelling arguments to go with an 11.5" gun. There's a reason BCM's shortest guns are 11.5".

There is an argument 14.5" is about ideal but personally I prefer 16" because I don't think 14.5 would be worth a stamp nor do I think the slightly shorter barrel is worth the drawbacks of a permed muzzle device.

In 300 black one can go down to 8.5" and still have good performance.

For 9x19 I would go as short as 4.5"-5.5". But that is because I would run it suppressed almost all the time. Otherwise I might want it a little longer to have a little more handguard space.

Heck, if you're gonna go short, go SHORT!

https://www.youtube.com/watch?v=cmZSFBy9CZ8

I have 10.5" in 5.56 and 7.5", 8.5" and 10.2" in 300 BO SBR's.

I consider the 10.5" 5.56 to be 100% reliable with any ammo I pour into it. Its never hiccuped . Velocity is down a good bit. 2450 ish from XM193 but I still pull 2500-2600 FPS out of 55 grain handloads depending on the charge. H4198 agrees with 55 and 62 grain bullets in SBR's IMHO.

The 300 BO's ? You could put a 4 inch barrel on that caliber and it would probably run just fine.

No problem with loud blasts because there is always a silencer attached.

I have a 7.5" 5.56 Piston upper that is fun to shoot and I am able to make torso hits on steel out to 200 yards fairly easily with a Trijicon RX06 optic. Its a PDW type of weapon and not really intended for engaging at that distance.

If I needed to configure it for an all-around balanced rifle, I would swap the upper for my 14.5" M4 upper and be completely happy with it.

taliv said:

i would not recommend a cheap barrel or a barrel that has been cut down. i would not expect them to be reliable.

Click to expand...

What do you consider cheap?

My 10.5" is a no name heavy barrel chambered in .223 Wylde. Only manufacturers info I got from the seller (Classicfirearms.com) was "government contract overrun." It cost me $74.99+S&H.

I do agree with not using a cut down barrel, but lower cost barrels have been just fine.

Considering that the gas pressure is higher and the port will erode much faster, putting money into an expensive barrel vs one that is GI spec may well be a waste. And having a heavy barrel - no point. It's a long range precision thing, to keep it from warping as much under long strings of fire. On a 10.5" PDW hosing bullets at close quarters, a heavy barrel will still get hot, and it will also take longer to cool off, too, with no recordable increase in accuracy.

This isn't a .5 MOA gun we're talking about.

No discredit to SSK on the .300 Whisper - but I was on Chapman Range that day and a competitor was walking the line showing not only his handloaded .30x 5.56 wildcat but knowledgeable about the rules. Taking his conversation at face value the rules were bent to eliminate him and the AR15 he came to shoot. Again, this was about 1984, and SSK's efforts came later. It's a matter of fact that 3 Gun didn't accept 5.56 for some time - and became a lot more widespread when it did.

Nothing wrong with .300BO, but when considering an AR pistol and my experience with 6.8, I decided that cheap surplus .Gov ammo was trump to an incremental increase in power - which is relative to the barrel length anyway. I could accomplish having 1,000 foot pounds of force out to 80m and get cheap ammo, too, for practice by having 5.56. I saw it as a win-win. I had my schooling with 6.8 about alternate cartridges, and if I reloaded would likely shoot it a lot more. For now the 5.56 meets my needs.

This is only my experience but, of the 2 pistol uppers I have the one with the most rounds through is as a pistol is a cut down Armalite upper. I've had no known issues with it at this time but only have about 500 rounds through it as a pistol. Accuracy seams fine to me but I've never actually benched the gun at 100 yards. It does shoot the same as it did as a carbine, at least at 25 yards.