Different barrel lengths on my registered SBR?

[Alpha231]

I originally configured my lower to have a 10.5" barre/upper. I want to get a 12" LMT piston barrel to go into my MRP. What are the laws around multiple barrels and uppers?

Thanks,
Eric

[m4fun]

Let me first say this is often questioned, debated, etc. The laws are just as fuzzy of having a registered M16A1 lower that says .223 and you want to fire 9mm or .22 through it.

You really have free reign, but...

I believe a letter to the ATF stating you intend on swapping uppers between lengths 10.5" to 14.5" barrels will cover your options. If there are any problems with this...

Naturally CYA by having a copy of the letter, and a send it certified. Keep any retrurn correspondence, copy it all and laminate it, stick copies in your range bag

[eternal24k]

As mentioned you can send a letter stating what length you intend to use.
I cover all calibers and lengths on my Form 1, originally listing multiple figures in the barrel length and caliber box, but now they don't like that so (under guidance of my examiner) I list in box H as "other calibers" and "other barrel lengths"

[tip2oo3]

Your original form1 should have the shortest overall length you intend to use. If that form1 was approved when you measured a 10.5 barrel, any length greater than 10.5 will be good to go. You can register your lower for 10.5 and use 11.5,12.5, 20+ or whatever. On the flipside if you wanted a 7.5 barrel you would need prior approval and modify your original form1.

[SuicideHz]

So you are also asking about simple possession of these multiple uppers, not just changing them out?

According to most people, all you are in jeopardy of is "constructive possession" and the simple way of putting it is this- you can have as many short uppers as you want as long as there is a legal configuration available for any and all non-SBR lowers you also possess. Legal configuration means you need to have a 16" upper for all non-SBR lowers in order to be able to possess more than one short upper for that SBR lower.

[Alpha231]

So you are also asking about simple possession of these multiple uppers, not just changing them out?

According to most people, all you are in jeopardy of is "constructive possession" and the simple way of putting it is this- you can have as many short uppers as you want as long as there is a legal configuration available for any and all non-SBR lowers you also possess. Legal configuration means you need to have a 16" upper for all non-SBR lowers in order to be able to possess more than one short upper for that SBR lower.

It would be extremely hard for the BATFE to associate any of my LMT MRP barrels (as they are proprietary to the MRP upper) on any non-NFA items... This is what I have going for me... your thoughts?