Re: Shortening AR-10 Barrel
A 16" barreled AR-10 with a rifle length gas system is generally a BAD idea! It is likely that your rifle will not function well (reliability will suffer in other words due to gas problems/short-stroking/etc.).
The problem is that with a rifle length gas system on a 16" barrel, you will only have an inch or so of barrel extended beyond the gas block which isn't enough length to ensure 100% function. This is why Armalite went to a mid-length gas system on their 16" barreled AR-10s which is roughly 3.25" shorter than the rifle length setup.