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Legal info wanted for building AR15 .300 Blk with 12.5" barrel (non-suppressed)

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I would like to build out an AR15 platform in .300 Blackout with a 12.5" barrel but I am really confused about the various legal issues and NFA requirements (tax stamp) ect.  I don't really care about suppressors at this time and don't plan on using suppressors presently, so for this build that isn't an issue.  Does anyone know of a good guide regarding this topic?  I am a little confused between things like SBR and AR15 Pistol.  How do they differ physically?  How do they differ legally?  What is required concerning NFA rules and regulations to build a 12.5" barrel AR15?

So many questions, so little time 🙂

I am in the process of building out my parts list and plans but would like to know what sort of legal hoops I can expect (or not expect) concerning NFA requirements so I can plan appropriately.

Thank you in advance!

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Do you want a stock? Not a brace, but a real stock? I ask this first question because it will give direction.

For me, an AR Pistol without a stock was pretty much useless, so that puts it into an NFA SBR.

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Do not buy an upper until you have decided to go SBR (and have an approved stamp), or a pistol brace.  I don't do stamps, I use mine as a pistol with a brace, if that becomes an issue I will address it then.

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  • 4 weeks later...

There are some pretty cool braces out that extend and make it more comfortable than the standard Pistol tube with a sig brace. To go SBR, it takes less than 30 days to get a stamp to make a SBR.

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If you're building from scratch, my recommendation is that you don't have all the parts until you receive your approved Form 1.  To have all of the parts without the tax stamp, even if they are not assembled, may be considered as "constructive possession."  That's not a headache you want to deal with.

If you change course and don't build from scratch, my suggestion is to purchase a gun that is configured as you like albeit with a pistol brace.  Then submit the Form 1 and install a stock once you've received back the tax stamp. 

Another alternative is to purchase the rifle you want albeit with a longer barrel than what you want.  Once you receive your tax stamp you can switch out the barrel or entire upper to the length you desire in accordance with what you put on your Form 1.

Side note: you can have different length  barrels and different calibers that you use on the one registered lower.  Just always keep the length/caliber listed on the Form 1.

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Side note: you can have different length  barrels and different calibers that you use on the one registered lower.  Just always keep the length/caliber listed on the Form 1.

You always have to be able to put it back in the configure it back to the original, think a lot of folks miss this!!!

I have another upper in a different caliber and length, you can just email them and they will send back a acknowledgment letter. Then you can just swap back and forth.

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