Just wondering if anyone has luck installing a factory Colt 7.62x39 upper on there M-16's?
Sure. Friend of mine has an all factory Colt 16" 7.62x39 upper he shoots. I've got a couple factory Colt 16" 7.62x39 barrels I'm running in DPMS upper receivers.
I've been running full auto 7.62x39 uppers for at least a decade.
I started out running them on regular M16 lowers and have been running a RDIAS for about at least the last 5 years to run the MGI lower and use unmodified AK mags and drums.
If you have a standard AR lower then you'll have to settle for the 'frankenmags' or the Cproducts/ASC mags.
Old video running frankenmags
MGI lower w/ 75 round drum
Its been done. The problem is mags if you aren't running an MGI lower and can use normal AK mags for it.
I don't have a Colt upper, but i have been shooting a model 1 11inch for many years on one of my m16 lowers. I've never had a problem, and never busted a bolt. although that maybe because I bought a bunch of that Vector Rhodesian brass x39 years ago. I haven't shot much russian steel. i've heard that steel users regularly bust bolts? YMMV. As far as mags go, if you can find the GTech mags buy them up. they'll run and run and run with no problems. I bought a bunch maybe 10 years ago. don't know if they're many around anymore.
all in all, i enjoy using my x39 upper. flamer thrower get one you'll be impressed it you have the good luck I've had.