I’m currently in the market to build a 9mm “other” firearm, which qualifies as neither a pistol or rifle. In order to meet that qualification, the firearm has to:

Design: (non-NFA firearm designed to be used with two hands)
Dimensions: (HAS to be greater than 26")
Configuration: (NEEDS A BRACE, and a VFG)
Method of Operation: (semi-automatic, not automatic)
Materials: (metal, plastic, same materials)

I’d like to barrel to be as short as possible, but still get to the 26” requirement, measured from barrel (not flash hider) to buffer tube.

Does anyone have any proven configurations that get me there?  12.5”, 11.5” or 10” + A5 buffer tube? Any sort of buffer extension?

I’m trying out a 10.5” barrel with a pinned a2 Flashider and regular pistol buffer tube. Not sure if it’s going to meet the 26” oal length. If not I’ll use a longer Flashider. I read that 11.5” with a pistol tube meets it

Be careful of how the "barrel length" is measured by the manufacturer. Most (in my experience) are measured from the chamber face to the muzzle, so they tend to give the firearm an overall length about 1" less than a 5.56 barrel since there is no locking lug barrel extension on the chamber end. Some of the measured barrel length is inside the receiver.

Some manufacturers really confuse things by measuring them from the receiver face to the muzzle as if the 9mm barrel has a 5.56 style locking lug extension, which they do not.

CMMG RDB 9mm DO have a locking lug extension, but I'm not sure how they're measured - I'd assume like a 5.56 barrel.

Someone correct me if I am totally wrong or have it mixed up.

I believe an 11.5 inch 5.56 barrel with a standard carbine buffer tube is just over 26 in. With a standard 9mm barrel, I believe you would need it to be at least 12.5 in.

On my 9mm AR pistol, I am using the Kak Super Sig SB15 buffer tube (which is longer than standard pistol?carbine buffer tube) and a Rock River 10.5" barrel. From the end of the buffer tube to the shoulder of the A2 flash hider is 26 1/16" and to the end of barrel it is 26 5/16". If you use a standard pistol/carbine buffer tube, you will most likely need to use a 11.5" or longer barrel. You might be able to get away with a 10.5" barrel if you pin and weld.

Attached File

Barrel has a specific measurement method used by the ATF - bolt closed, from bolt face to last permanently attached part of the barrel.  This means if your muzzle device isn't pin/welded or silver soldered on or some other ATF approved method of attachment it doesn't count.

But barrel length isn't exactly relevant for this question as long as a "stock" (not a brace) is not involved - it is overall length, MINUS any pistol brace - just whatever buffer tube/extension you are using on the back end, and up to the front end to the last part that is permanently attached (same as above on muzzle device basically).  

And this week, if you're using a folding buffer tube, ATF measures the buffer tube folded, IOT screw over some Connecticut "firearm" owners.

To get over 26" OAL with a 10.5" barrel without pinning and welding the muzzle device, you will need to use something like the Kak Super Sig Brace. When I measured my pistol last night, it was from the end of the buffer tube. The Sig SB15 sits flush with the end of the buffer tube.