I did a little research on this and didnt find any threads relevant to my question, so my apologies in advance if this has been asked before.

I had an idea about picking up a 16" upper (or longer) with a carbine gas system (Piston wouldnt suck either though) and chopping it down to 10". now I understand that doing this will require an NFA which is current sitting around the fed office somewhere waiting on approval. but my largest curiosity is will cutting the barrel down affect the operation of the weapon itself? will it still cycle properly? and if not what can be done to remedy the problem. would it be smarter to just buy a 10" upper and be done with it? Just would like to see if anyone has any insight on this project I have in mind, any help would be appreciated!!