ive purchade a sundevil ar15 and cant figure out why it wont chamber a second round, I can put a lower of another rifle and have the same problem so it must be in my upper. the only way I can get it to chamber is to put a short buffer from a carbine in it. it is a rifle buffer tube at 8 3/4 lenth and I know this isn't good. ve checked the gas tube and it seem fine, no blockage. I have used my mags in my other ar and they work fine. ive also change out the bolt assembly from my other ar and it still does it I don't know if its shortstrokin or not but with the short buffer it seems fine. I have even put the long rifle buffer with the short carbine spring, still wont feed. I guess im missing something somewhere and cant figure it out id hate to just throw the upper away. hope someone out there can help me.