So I've reached The End. The bottom of the barrel. The I-have-everything-I-want-so-now-it's-time-for-ridiculousness time.

It's time for a Grenade Launcher!

Specifically an M203.

I'm looking at these three LMT's:
https://lmtdefense.com/product/9-rail-mounted-m203/
https://lmtdefense.com/product/9-m203-pistol/
https://lmtdefense.com/product/9-sta...-mounted-m203/

I want to be able to use this different ways:
Mounted an a 16" rifle
Mounted on an 11.5" SBR
Stand-alone as a pistol
Stand alone with a buttstock

I selected the 9" version as it seems like the Goldilocks length and I can swap the barrel if necessary.

A few questions...
Which version should I buy that will allow me, within NFA rules, to use it in all these configurations? Should I be looking at a different model?
Obviously I'm buying it on a form 4 but will I need to do a form 1 to use it in a different configuration? I guess what I'm asking is if I buy the mounted version and add a stock will it require another stamp? What about the buttstock version and then mount it to a rifle or use it as a stand-alone?

Also, I'm definitely going to pick up a hornet's nest or similar... besides chalk and smoke, what cool things do you all shoot these things?