View Full Version : Problem with new AR build

02-17-2008, 7:41 PM
I've been saving to make my first post a (hopefully) relevent one.
I have a problem with my new build. I have an A3 18" SPR type CMMG upper with a mid-length gas system, mated to a stag lower with a Timney modular trigger group. Everything is brand new and well oiled. I took it out to the range yesterday and experienced what I would call weak ejection of the spent casing. It would drop the casing right on my (table rested) elbow, with not very much force at all. Additionally, after firing off a round, the next round would feed properly but fail to fire (no hammer strike). Manually cycling the charging handle, ejecting the FTFire , and loading a new round would start the cycle all over again. I also noticed that after firing the first round in the sequence, that if I placed my trigger finger behind the trigger and applied forward pressure that the trigger would then reset and all would be well.
Is this a case of weak ammo (I'm using PMC bronze line 55gr FMJ) where the bolt is not traveling fully rearward? Or could there be something amiss with the Timney modular trigger group? I have several (4) CA compliant AR's in various configurations, and have never experienced anything like this before. Just looking for opinions and a little guidance before I start to tear into this thing. Sure shoots good though!

02-17-2008, 7:44 PM
It sounds like your FCG is not installed properly, my guess would be that the bolt carrier is hanging up on the hammer .

I would focus on the trigger return spring as I suspect that may be installed incorrectly.

02-17-2008, 7:52 PM
Thanks AJAX, but with the Timney modular FCG I dont think I can get to all of those little parts. Or can I...

02-17-2008, 7:53 PM
When you sit at home and do function checks, does the mechanism appear to be working correctly otherwise? Can you cycle snap caps without using undue force?


02-17-2008, 7:59 PM
Everything function and safety checks ok. It all works very smoothly without any noticeable hitches or weird noises.

02-17-2008, 8:17 PM
What type of buffer spring is installed? Carbine or standard. if you need a carbine and have installed the longer spring, maybe the bolt is not retracting the hammer far enough for the disconnector to grab it. maybe to much dension. Spring might let the bolt move back for a weak extraction but not enough to set the hammer.

02-17-2008, 8:32 PM
Thanks Mason,
I'm using an A2 stock with the rifle buffer and spring. I had the same thought about restricted bolt/carrier travel. So many variables...could be this, could be that. I think I'm going to start by replacing the Timney unit with an RRA 2-stage FCG that I have laying around, then take it out tomorrow and see if the problem repeats.