- Mar 31, 2008
I'm wondering how you guys decide on barrel length for an SBR. It seems like 10.5 is pretty middle of the road, so I put that on my form 1, but I'd be interested in hearing why you chose a certain length.
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Q: Why BCM chose the 11.5" SBR over the 10.5"
I get this question a lot. It is a good one. When we spec our program we can build anything we would like, so we sat down and looked at the pros and cons.
First Statement: I know a good 10.5" SBR can run very well. I personally own a semi MK18 type and it runs great. No problems.
A: Dwell time.
Dwell time is the time that your gas operated weapon maintains pressure to continue the cycling of the weapon. It primarily exsists from the time the bullet passes the gas port in the barrel to the time the bullet exits the muzzle. When you pull the trigger and fire the weapon the movement of the bolt carrier group unlocks the bolt, extracts, and ejects the spent casing. Then it cocks the weapon, feeds, chambers the next round, and then locks again. One of the thing that can make SBRs finicky is the dwell time (or lack of).
The 11.5" carbine is approximately 4% longer weapon than its' 10.5" counterpart, but this extra inch gives the barrel a 40% increase in length for dwell time. IMHO, this is an excellent trade off. This additional dwell time (all other things being equal) will allow the carbine to be more forgiving to different ammo types, extremes in air temperature, weak or worn extractor springs, worn extractors, buffer weights, etc.
Last Statement: For those folks who have a 10.5" that works very well, I would reply; me too. (see first statement)
If I had to "go to war" with a AR15 Carbine, I would grab the BCM 11.5".
The BCM 11.5" Runs Like a Dream.
Hope this info helps,
this is great info.Here's some info to help you decide:
Speaking of non-NFA 9mm ARs, Palmetto has started to offer a "pistol kit" to build out any stripped AR lower into a 10.5" free-state-legal 9mm pistol:I was initially thinking 9mm for that same reason
I wouldn't go shorter than 10.5 on a .223 if only because it pretty much becomes a machine for emitting fireballs rather than bullets with an effective velocity.10.5 because I heard shorter does not run well...If you want to see some great 10.5's look at noveske.
The 45 will be gas , less recoil and don't need a 1.5 to 2 pound bolt . But gas blot is tight next to the barrel nut. If I move to a free state or get my shop rezoned so I can apply for a FFl I could run a can and have it the same length as the 5.56 barrel .As short as you want, there is no gas system to worry about. I am looking at 5" for my 9mm because I am eyeballing a TiRant 9 which is ~8" long, so I can tuck it all under a ~10" float tube of some sort and look boss.
Haven't had any problems with mine, but I don't run that many rounds through it. It's just a fun toy to make people at the range stop and lookI was going to go with a 7.5" but I've read a lot of info about them having issues. Going with a 10.5" Carbine gas system for the extra reliability.
For 9mm with a suppressor, seems like a lot of people go as short as 4.5", micro-uzi style.I went 10.5 with my 5.56. Didn't see the bcm article at the time, but I'm still happy with my choice. For 9mm I'm considering 5" with a vfg, but question how it will look/ handle. Maybe 7" is better?
That's my current thought, but I'd go with a shorter rail, just because I prefer a half inch or so of the suppressor extend out, like so:As short as you want, there is no gas system to worry about. I am looking at 5" for my 9mm because I am eyeballing a TiRant 9 which is ~8" long, so I can tuck it all under a ~10" float tube of some sort and look boss.
Buy a pistol buffer tube (cheap), and then buy the barrel and build the weapon up as a pistol. Shoot the shit out of it waiting for the stamp. When the stamp comes in, pull the pistol buffer and replace with a stock.So, I'm waiting on my stamp approval... You know, again... And I'm wondering, can I buy the barrel before the stamp gets approved, or should I wait it out. My gut feeling is to play it safe and wait to get the stamp back. What say you?
Just buy the barrel now if you want to. As others have shown, the idea of constrictive intent also leads to a pistol build.So, I'm waiting on my stamp approval... You know, again... And I'm wondering, can I buy the barrel before the stamp gets approved, or should I wait it out. My gut feeling is to play it safe and wait to get the stamp back. What say you?