SBR barrel length

[outrider58]

So they do it while you wait?? Seems reasonably priced also for $50.00

Most places(gun shops) that do laser engraving will do it while you wait as long as the person who runs the machine is there. Usually best to call ahead if you don't want to leave the part.

 

[woodline]

Are the gas port locations different on a 10.5 & a 11.5” or 12.5”

I run a mid length 12.5” triarc barrel, but that is for dedicated suppressed use. It is awesome.

 

[alucard0822]

So they do it while you wait?? Seems reasonably priced also for $50.00

If Phil is at Lanco Tactical and isn't occupied, he'll do it while you wait, although I usually end up dropping a few at a time, or buying lowers from them on the shelf, and pick them up later in the day, or a couple days later.

Are the gas port locations different on a 10.5 & a 11.5” or 12.5”

I run a mid length 12.5” triarc barrel, but that is for dedicated suppressed use. It is awesome.

There are 3 main things that affect gas tuning in DI ARs, gas length, port size, dwell length. The gas length is basically how far down the barrel the port is located, the further away, the lower, and more consistent the pressure. Pistol=5", carbine=7", mid=9", rifle=12", measured around the mid-point of the chamber. Port size will regulate pressure/volume, this is really the only thing an adjustable gas block adjusts. Dwell length is how much barrel there is after the port, and how long/how much volume of gas is available. This is for 5.56, other calibers have different requirements, 300BO tends to need big gas ports and relatively long dwell(almost always pistol or shorter) due to the small volume of fast powder.

A 20" rifle length AR has about 8" of dwell, 14.5" carbine gas M4 has 7.5". This is more than enough gas to ensure operation in adverse conditions, and takes a heavy buffer to help smooth out the bolt velocity to handle a wider range of ammo burn rates and port pressures, but at the expense of gas blowback and recoil. The current flavor is shorter dwell and larger ports, this cuts some of the adverse things with overgassed rifles, and can still function reliably, even if that shorter dwell and higher pressure can make buffer tuning and ammo selection a little more important. A carbine gassed 10.5 or a mid-length 12.5"is a mere 3.5", 1/2 the dwell of M16s and M4s. This can be a better choice than short pistol length gas in 5.56 rifles, being the first 3-6" of barrel is where pressure from different powders varies the most, a port after that will be more consistent. The shorter barrels have a lower velocity anyway as the bullet keeps accelerating as it travels down the barrel. That 3.5" of dwell may result in close to the same amount of time the system is pressurized as 5" of dwell in rifle gas barrels, but with more pressure on tap. The real magic comes with suppressors, that short dwell really cuts down on gas blowback, there is less residual gas to your eyes and to cause reliability issues.

I can run a can on my 10.5" carbine gassed AR, and pretty easily find a setting where it runs well with or without a can, even works with gas wide open just a little more recoil and gas in the face, I use an H3 buffer. Doing the same on a 16" carbine gassed barrel with 9" of dwell gives a really harsh recoil anyway, add a can and it takes some work to run reliably while blowing gas out of every nook and cranny. The old adage of 6-9" of dwell is kind of dead outside of .mil, and 3.5-6" of dwell in a quality barrel shorter than rifle length gas tends to do just fine without a can, and is superior with one.

 

[outrider58]

Given this is the OP's first SBR build, I would recommend he keep things rudimentary. Barrel between 10"-12" range and carbine gas. He should not encounter any drastic function problems with that formula. There's plenty of time afterwards to dive down the rabbit hole.

 

[calicojack]

Carbine length is the way…

I actually have a 14.5" SBR that has a mid-length gas system from BCM; seems to run fine but definitely an odd-ball.

 

[outrider58]

I actually have a 14.5" SBR that has a mid-length gas system from BCM; seems to run fine but definitely an odd-ball.

BCM was really pushing them. They do soften the impulse while shooting full power 5.56. I've read about guys(even on here) about cycling problems using lighter loads in race guns and such.

 

[calicojack]

BCM was really pushing them. They do soften the impulse while shooting full power 5.56. I've read about guys(even on here) about cycling problems using lighter loads in race guns and such.

Good to know.

 

[calicojack]

BCM was really pushing them. They do soften the impulse while shooting full power 5.56. I've read about guys(even on here) about cycling problems using lighter loads in race guns and such.

Honestly, the main reason I got the mid-length is I like irons and I like the sight tower out further for a longer sight radius.

 

[jrumann59]

Honestly, the main reason I got the mid-length is I like irons and I like the sight tower out further for a longer sight radius.

I have an AR with a 16 inch barrel with front site right behind the muzzle device. First time shooting it was a little weird, you wouldn't think so but it was you expect to see a little more of your muzzle.

 

[boothdoc]

Thanks again to all those who have responded. I am all ears and soaking up what I can.

 

[teratos]

I actually have a 14.5" SBR that has a mid-length gas system from BCM; seems to run fine but definitely an odd-ball.

Oh, I bet it shoots nice, though.
I just bought a 12.5” barrel. Carbine length buffer tube, with FSB. I have a sweet Daniel Defense rail on my shelf I need to use. It will eventually get its own lower. It’ll be my night vision upper.

 

[boothdoc]

I have to laugh. Every time you knowledgeable folks I have to google the acronyms used.
Now to research FSB , lol.

I don’t mind at all and I am not complaining just figured I would share what I find to be humorous.

 

[boothdoc]

FSB= front sight base??

 

[teratos]

FSB= front sight base??

Lol. Yes.

 

[calicojack]

I would highly recommend this BCM 12.5" barrel upper for an SBR. It is a "kino"" configuration, which is a carbine length gas system, but with a mid length front sight tower. Even with a red dot, I like to have the front sight.

https://bravocompanyusa.com/bcm-standard-12-5-carbine-upper-receiver-group-kino-configuration/

 

[MichaelZWilliamson]

You can't register an upper because it is not a firearm, and you should not attempt to do so because it might encourage ATF to start treating them as firearms, as they have already threatened. That would mean two stamps.

You should register the shortest configuration you have. Registering, say, a 14.5" and then swapping for 10.5" greatly changes the function of the weapon for example, entry.

You can then note, "this short barreled rifle has also been set up with a 14.5" barrel" just to have it officially on file.

Just as with suppressors, you can shorten a can, but you cannot lengthen it.

Just went through this when their records of one of my SMGs didn't match what was on the Form 4 or my measured length. Complicated story, but everything is legal and was resolved with a letter they stapled to their copy, apparently.

 

[outrider58]

You can't register an upper because it is not a firearm, and you should not attempt to do so because it might encourage ATF to start treating them as firearms, as they have already threatened. That would mean two stamps.

You should register the shortest configuration you have. Registering, say, a 14.5" and then swapping for 10.5" greatly changes the function of the weapon for example, entry.

You can then note, "this short barreled rifle has also been set up with a 14.5" barrel" just to have it officially on file.

Just as with suppressors, you can shorten a can, but you cannot lengthen it.

Just went through this when their records of one of my SMGs didn't match what was on the Form 4 or my measured length. Complicated story, but everything is legal and was resolved with a letter they stapled to their copy, apparently.

AFAIK, you register the lower(serial #), but engrave the barrel. I have never done this, nor would I, but I have heard of people doing this legally.

 

[MichaelZWilliamson]

AFAIK, you register the lower(serial #), but engrave the barrel. I have never done this, nor would I, but I have heard of people doing this legally.

No, you engrave the receiver because that is the firearm, therefore the SBR.

I have an entire vault full of NFA here, and I keep a firearm attorney on retainer.

The barrel is not a firearm. (Though much of the world does define the barrel as the functional part.)

 

[outrider58]

No, you engrave the receiver because that is the firearm, therefore the SBR.

I have an entire vault full of NFA here, and I keep a firearm attorney on retainer.

The barrel is not a firearm. (Though much of the world does define the barrel as the functional part.)

Never said it was, but you might want to tell that to Ruger as well as a few other firearms manufacturers, and I too have a vault full of NFA goodness.

 

[atblis]

I don't believe there's anything wrong with engraving additional barrels either.