I took a RR to the range today and had a couple issues I figure somone here would have some input into.

First:  Firing brass and steel cased in this upper causes it every 2 to 3 rounds a mag (sometimes every round) to close the bolt with an unfired round in the chamber and the hammer dropped.  EX:  fires, strips next round, no bang, trigger will not reset as it is all the way back.  

Second:   Firing steel a couple times a mag the same thing happened as above.  Brass worked fine.  

Third:  This upper which was working fine on a different M16 lower would fire until the LAST round which would end up in the chamber unfired, hammer down.  Steel cased ammo, it did this two mags in a row.  

Three different uppers.   All were used on semi guns before this.  

Brass worked perfectly in the second upper.  

We actually had a fourth upper which was fine with brass but short stroked with steel.   I understand that was undergassed as it did not consistently pick up the next round.  

Opinions on any of the issues with the separate uppers?

I didnt think to put the first or second upper on the perfectly working M16, we ran out of time and ammo.  

Thanks in advance.  

FYI: standard carbine buffer in the working M16 and the problem one.  Both the exact same buffer, spring and tube.  

thanks again for the help.  This is my first run at diagnosing M16 issues.

It sounds like bolt bounce to me. Assuming you are running a collapsable stock I'd try a H2 buffer.

x2.  Try a heavier buffer.  I had a very similar situation as you described.  



I need to run a H3 buffer when I run full auto with a suppressor and a 11.5" barrel.  A H2 will work unsuppressed.



 

What's your rpm with ammo that works?

Are you using the same buffers from your semi guns?

It sounds like bolt bounce. If you don't know what that is, basically when the fun us running fast and the bolt closes it hits the barrel extension and bounces back causing the falling hammer to drop before the bike is in battery and the firing pin is contacting the primer.

Running a standard buffer.  Just dug up a H buffer from the spare parts bucket.  I will give it a try next range trip.   Thanks