What would cause this malfunction (doubling)?
Ok, here's the situation.
The setup: New Daniel Defense M4 carbine. 16" Carbine length gas system. Complete factory rifle. Took it to the range to zero the iron sights and get a feel for it. Ammo was a mix of Q3131 and Remington 55gr FMJ. Magazines were a mix of Lancers, PMags, and TangoDown ARCs. I've contacted Daniel Defense and have not heard back yet. It's a holiday weekend, so I don't expect a reply for a few days.
The malfunction: Shooting from a bench, using the magazine as a monopod, I would get occasional (1-2 per magazine) doubling. One trigger pull, two shots fired. This occurred with all three types of magazines, and both types of ammo. No consistency as to WHERE in the magazine the malfunction occurred.
Took the lower off and did some experimenting. Below is what I found.
1. cock hammer manually
2. pull trigger and hold to rear
3. recock hammer manually (trigger still to rear)
4. place thumb on hammer and press downward and release
5. hammer falls on it's own accord almost 100% of the time.
Did the same with a friend's Noveske and hammer never moved in step 4 and 5.
I understand how all the parts in the upper work together, but lowers are a bit of a black box to me. I don't plan on fixing it on my own, since it is a new factory built gun, but for my own education, I'm curious as to what the cause (or causes) could be.
Any help would be appreciated. As soon as I hear from the manuf., I'll be sure to post an update in this thread.
Thanks,
Jason