WE M4 Open Chamber Fire Mode Issue
 

Recently I had an issue with my WE M4 OB where the rifle wouldn't fire unless I inserted a magazine with the bolt locked back. This quickly degenerated into the rifle going runaway on semi, stopping only when I dropped the magazine. I replaced the trigger group with a Ra-Tech group, and all was well for a week. Today I decided to fire off at a couple of targets. Rifle starts doing burst fire on semi-automatic. I open it up, and inspect the trigger group. Nothing looks like its out of the ordinary. I'm at a bloody loss.

Two thoughts:

1. For some reason the bolt is short stroking and thus the hammer isn't locking back. An NPAS was installed, but otherwise everything is stock. I suspect this may be in part due to the OEM bolt hitting the upgraded parts- I can see a divot in the bolt carrier forming, and a steel carrier is my next upgrade- I'd like to fix this first though.

2. The problem doesn't exist when I firmly pull the trigger back all the way... it's when I creep it back to the breaking point it goes auto when it sits on that breaking point. I don't want to say it's the trigger group since two exhibit the exact same issue. But I'm tempted to throw in a CWI hammer and disconnect and see if that fixes anything.

Any ideas? I'm completely stumped.

check your sear. It sounds like an issue with the sear anyway, as its worn down and not allowing a full trigger reset.

I read on gasguns.info that the RaTech parts aren't dimensioned 100% to the WE parts, so I just stripped out the two trigger boxes I had and took a look. The original disconnect and hammer were okay, then I remembered that for some reason the bolt had kept bumping into the RaTech sear when I first installed it, so I had replaced it with the WE sear. Swapped the original hammer, disconnect into the RaTech box, and also put in the RaTech Sear.

Problem fixed, at least for now. I hope. Doesn't explain why the sear started working when it had kept hitting the bolt in the past though.

Yea it will work for now, but because WE parts are aluminum or pot metal (I can't remember which), and the other parts are steel, they will wear out fast. I would compare each part and then take a dremel and grind the parts down to roughly the same dimensions. It's what I did with my AWSS WE M4 and it worked perfectly afterwords.

If anything, it seems like I would need to add material to the Ra-Tech parts to machine them down... where the WE OEM has straight edges and sharp corners, the Ra-Tech parts have more of a contour. The only parts not OEM in that trigger box are the trigger, the valve knocker, and the sear. I'll keep an eye out for issues and wear, but I guess i'll have to grab another set of aftermarket trigger internals not from RaTech when the time comes.

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