Posted: 1/15/2010 8:20:40 PM EDT
| I have a S&W M&P15 lower. I just received my new CMMG M4A1 SOCOM upper. I chambered the first round and it fires with no problem. The next round is chambered but will not fire. There is no pull to the trigger. Upon inspection, the chambered round is intact but has a firing pin mark on the primer. Any ideas or questions? |
| Hmmm... Well a failure to cock can mean short recoil. With a new lower, I wouldn't think that's the issue. Basics first- check lube, and carbon buildup in receiver, carrier and carrier key. Those are obvious. Next I'd check the gas rings around the bolt, stagger. Then I'd check the gas tube for cracks, looseness around gas block. Then I'd check the alignment of the carrier key to the gas tube. Maybe take a look at the buffer, is it the right weight? |
| I took the upper and put it on a second lower of mine. This time, on a dpms lower. The gun performed flawlessly. I took my buffer and spring from the dpms and put it in the m&p and it still wouldn't cock the hammer. Next I am going to check the internals on the LPK of the Smith & Wesson lower. |