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1/22/2020 12:12:56 PM
Posted: 10/8/2007 6:15:10 PM EST
I've been approved for SBR's for three AK kits that I'm going to build. I was also recently approved for an Arsenal SLR 106CR SBR. Getting the barrel length and overall length for the kit builds was pretty easy because the specifications were available online. For the 106CR, I just took both measurements and took away the amount of barrel that I'm going to chop off.

1) Now I'm in the process of putting together an AR15 9mm SBR build. I've purchased a complete CMMG lower half with the magazine block already installed. For the upper half, I want an A2 upper, M4 handguards, an A2 front sight post. CMMG has what they call an 11.5" upper. Does this mean that the barrel length will be exactly 11.5" to the bolt face? Or, is there an amount that I need to adjust this number by?

2) I also want to build another upper half with a really short barrel (say 5" or so) to mate a suppressor to. Should I list this barrel length on the form 1 too?

3) What about the overall length? I can't actually measure it due to the fact that I don't have the upper purchased yet because that could be considered "constructive intent". Is there some sort of formula that I can use to get the overall length?
Link Posted: 10/8/2007 6:29:38 PM EST
the barrel length should be measured from the closed bolt face to the end of the bbl. However, since a FS is probably going to be attached to that upper, it should measure a little longer than the true bbl. length of 11.5".

Sorry I do not have the info on what the OAL would be. I'm thinking it should be 34.5" w/ an 11.5" bbl. though(totally unsure about this).

FWIW, if you plan on building another AR SBR, build the lower as a pistol, so you can go ahead and get your short bbl.
Link Posted: 10/8/2007 6:38:12 PM EST
Link Posted: 10/8/2007 6:41:48 PM EST

Originally Posted By tony_k:
Barrel lengths do not have to be that precise -- if you are buying an 11.5" upper, you can put down 11.5" for the barrel length on your Form 1. BATFE won't come after you with a micrometer.


Originally Posted By rcr29:
the barrel length should be measured from the closed bolt face to the end of the bbl. However, since a FS is probably going to be attached to that upper, it should measure a little longer than the true bbl. length of 11.5".

FWIW, overall length of a firearm is measured with the stock extended, but barrel length is measured with any removable parts removed. So unless you're planning on permanently blind-pinning the flashhider onto the barrel, you measure bbl length without it.


right. I was trying stating that if he tried to measure the bbl. it would come out to more than the true length of the bbl. if he didn't take the FS off. Thanks for clearin' up my muddy 'splainin
Link Posted: 10/9/2007 3:40:51 AM EST

Originally Posted By rcr29:
FWIW, if you plan on building another AR SBR, build the lower as a pistol, so you can go ahead and get your short bbl.

Duh! Why didn't I think of that? A friend of mine has an unbuilt pistol lower. I'll order the upper half and have it sent to his house. I'll then be able to take the measurements to the rear of his lower receiver. I can then add on the length of the tube and buttstock to get the overall length. I'll have the upper built without the flash hider installed so that I can get the exact barrel length. He can hold on to the upper until my form 1 is approved.
Link Posted: 10/9/2007 3:44:17 AM EST

Originally Posted By tony_k:
Barrel lengths do not have to be that precise -- if you are buying an 11.5" upper, you can put down 11.5" for the barrel length on your Form 1. BATFE won't come after you with a micrometer.

That's good to know. It's interesting that no directions are given in regard to how the measurements are to be written on the form. Should fractions or decimals be used? If decimals, to how many places? What tolerances are allowed? I just wonder if they really don't care or they're being intentionally vague. Has someone ever been prosecuted for having an incorrect barrel length on their form 1?
Link Posted: 10/9/2007 5:06:06 AM EST
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