NFA lowers plus modern uppers

[davepl]

Are there any "gotchas" (technical, not legal) in terms of compatibility of old M16 lowers and current M4 uppers? Or should I expect a pre-86 M16A1 lower to just fit into place with a Colt LE6940 M4 upper?

What about the collapsible stock from the M4? Could it also be fitted to the older M16A1 lower? I'm assuming I would need something like the Tapco "Collapsible Stock Conversion Kit" for fixed-stock rifles, but other than that?

Thanks!
Dave

 

[SpaceFrank]

An interesting question to which I would also like to hear the answer. Would there be any legal issues?

 

[kimbershot]

pin size .154?

 

[Quiet]

You can legally reconfigure your MG to however you like.

So, you can take your pre-'86 Colt M-16A1 and switch out parts to make it appear as a M-4A1.

 

[DoubleTapDrew]

I wish I could share my firsthand knowledge on this but alas, I cannot afford a RR yet. From the research I've done on the subject (because I'd like a RR or DIAS someday) you can switch out or mix n match whatever you want, so as long as the lower is mil-spec, all the mil-spec modern goods should fit. I'm pretty sure that stripped lower is the machinegun itself, so you can replace the internals with FA replacement parts as well. I'd just make sure the important stuff (pivot holes, other holes) are in good shape and not egged out or cracked anywhere.

 

[taliv]

welcome to THR

i bought an old bushmaster conversion of an essential arms receiver some years ago and stripped everything off of it and rebuilt it. geissele SSF trigger and kns pins, magpul ubr stock, quality lower parts kit, cmt upper with a carbon fiber barrel, kac TT brake, bcm bcg, etc.

works great

there are a few gotchas

the aforementioned small/large pin sizes that colt inflicted on law abiding gun owners for no good reason. it is of course possible to rip the crap off the old colt upper receiver and put new barrel, handguard etc on it, but it will probably be an A2 style with integral carry handle which is suboptimal. and it won't have m4 feed ramps in the receiver which is a big negative on a machine gun.

if you get a cast receiver like mine, the geometry of the receiver under the grip is different than it is on forged receivers and so some grips don't fit. that's why i am using the ergo on this gun instead of my fav magpul MIAD.

you shouldn't have any issues with stocks. don't put any tapco crap on a $10,000 receiver

i can't imagine any legal issues in a red state. not sure about blue states.

also, if you do decide to strip the lower, and especially if you get a cast receiver... MAKE SURE you do not break the ears off trying to get the roll pin out of the trigger guard