more_bullets
New member
I'm going to build an sbr in 300 blk but I'm not sure what barrel length I want...I was wondering what your favorite barrel lengths were and why! Thanks for the input! I'm thinking 10" probably.
300 blk sbr barrel length
- Thread starter more_bullets
- Start date
I have (and LOVE) my 9" AAC upper
Ive done it into a pistol and now an SBR, suppressor on the way
As for ballistics, dont beleive the oft cited "powder is all burned in 8 inch" myth
Even if it all "burned" in 8 inches the gas volume continues to expand so you DO get velocity benefit from longer tubes.
That being said the gain is not as much as other calibers so the 300BO is the best of the SBR rounds.
If you are going with only 1 gun in this caliber and think you might want to put a suppressor on at some point, id go 9". Very nice short length rifle. Easy to manage. Balances well. Good ballistics outta this length. With the can it comes out to about the same length as a 16" gun
One thing... Make sure whatever barrel you get it is running pistol length gas system. Wont be any question on a 8-10" barrel but 16" come both pistol and carbine gassed. Carbine gas is MUCH more finicky about ammo and gas pressure.
Ive done it into a pistol and now an SBR, suppressor on the way
As for ballistics, dont beleive the oft cited "powder is all burned in 8 inch" myth
Even if it all "burned" in 8 inches the gas volume continues to expand so you DO get velocity benefit from longer tubes.
That being said the gain is not as much as other calibers so the 300BO is the best of the SBR rounds.
If you are going with only 1 gun in this caliber and think you might want to put a suppressor on at some point, id go 9". Very nice short length rifle. Easy to manage. Balances well. Good ballistics outta this length. With the can it comes out to about the same length as a 16" gun
One thing... Make sure whatever barrel you get it is running pistol length gas system. Wont be any question on a 8-10" barrel but 16" come both pistol and carbine gassed. Carbine gas is MUCH more finicky about ammo and gas pressure.
more_bullets
New member
Thank you shark bite! Very helpful info! Sounds like 9" is the way to go. It will be suppressed at some point.
Theohazard
New member
I was planning to add some thoughts to this subject, but Sharkbite pretty much said everything I was going to say 
.
Though I want to strongly encourage you to make a suppressor a priority. The 300 Blackout is ideal with a can; it's stupid quiet with subs and with supers it's still a little quieter than a 5.56. I have an AAC SDN-6 that works great on both 300 Blackout and 5.56; you can put it on pretty much any caliber from .30-06 on down (though I highly recommend NOT putting it on a .22).
. Though I want to strongly encourage you to make a suppressor a priority. The 300 Blackout is ideal with a can; it's stupid quiet with subs and with supers it's still a little quieter than a 5.56. I have an AAC SDN-6 that works great on both 300 Blackout and 5.56; you can put it on pretty much any caliber from .30-06 on down (though I highly recommend NOT putting it on a .22).
Theohazard
New member
It's the lower that is registered as an SBR (and to build an SBR you'd use a Form 1; a Form 4 is for the transfer of an existing SBR). The barrel is just a part, whereas the lower is legally the firearm. And a short barrel isn't necessarily for an SBR, it's completely legal to put it on an AR pistol without any federal registration.
But here's where it can get tricky: If you have the parts required to make an SBR and there's no other explanation for you having them, then you could get in trouble for "constructive intent". Basically, they'd say you intended to make an unregistered SBR. So if you own a short barrel it's a good idea to also have a lower configured for pistol use (meaning the buffer tube can't accept a stock). That's the way most people do it while they're waiting for their tax stamp.
But here's where it can get tricky: If you have the parts required to make an SBR and there's no other explanation for you having them, then you could get in trouble for "constructive intent". Basically, they'd say you intended to make an unregistered SBR. So if you own a short barrel it's a good idea to also have a lower configured for pistol use (meaning the buffer tube can't accept a stock). That's the way most people do it while they're waiting for their tax stamp.
You could buy a registered SBR lower from a NFA dealer on a form 4. The same as buying a suppressor, but i dont know why you would with an AR platform
Just take a standard rifle lower and do an Eform 1. Easy pesy. Same wait time as a form 4 anyway
If you do a form 1 the lower needs to be engraved with your info (personal or trust) as you are making a new NFA weapon. If its an already made SBR lower it will already be engraved with whoever made it a SBR
Just take a standard rifle lower and do an Eform 1. Easy pesy. Same wait time as a form 4 anyway
If you do a form 1 the lower needs to be engraved with your info (personal or trust) as you are making a new NFA weapon. If its an already made SBR lower it will already be engraved with whoever made it a SBR