ar15 new build


I am new to building ARs. Have no problem with lowers.(so far). my 2nd upper build will not complete the cycle. does all of the cycle except for the last 1/4 to 3/8 of an inch.
any idea as to the problem so i know what to look for? the lower runs fine with other uppers.


That makes sense if the gas block is partially the gas port in the barrel. I didn't think of that.
Did you swap out the spring and buffer from another working AR?
make sure your gas block / barrel isn't slightly off level. That will slant the gas tube enough to place enough force on the gas tube/key interface to keep the bolt from going into battery.


well problem resolved. yall did good.
it was in the gas system, tube was off to 1 side(bent I guess?) i need to do a better job checking on the next build.
had to sand the tube & repair the gas port on the bcg. all's well now, ran 2 mags thru it & all went well.

thanks again