Forgive me for my ignorance.  I have assembled a few stripped lowers over the years.   All that I have purchased through an FFL have been marked “MULTI”.   Years ago I bought a complete rifle in 6.8 spc with the lower marked that way.   I have often thought of selling the upper off the 6.8 but had reservations about the upper/lower combination.  I guess I don’t understand the way the lowers are marked, either by caliber or multi.   Does it just have ramifications with pistol or rifle?   I only have 16 inch uppers and don’t mess with the pistol or pistol brace, etc....  Can I just sell the 6.8 upper?   Can I put whatever upper on a 6.8 marked lower?   Please explain.   Thank you.

Unless there is NY law to the contrary, you can put whatever caliber you like on the lower.  You can even mount a crossbow upper if you like.

Sounds good.   Thank you.

Yes. I've had Colt lowers that were marked 9mm, attached to a .223 upper.  The gun may have left the factory as a 9mm, but it was a .223 when I got it.

There is no requirement to put any caliber marking on the lower.  The caliber should be marked on the barrel just like a bolt action rifle.

I have a letter on it from ATF.  If I am not mistaken, Tromix was the first to omit all caliber markings from its lowers, beginning in 2000.

Tony Rumore
Tromix

Thanks for the info.