Problem with the field strip screw

[Maghog]

I recently put together a minimag with a z-grip, retro valve, and warp feed. The parts all came individually, and when I put it together, it did not fire. I was all ready to have to go over the entire gun, went to unscrew the field strip screw, and after only 1 full turn I hear a "click" inside the gun. I quickly aired it up and it worked fine.
I'm finding that tightening this screw too much will disable the guns function. This does not happen with my other mags.
Is there a problem I don't know about?
In the past I have found field strip screws that have been less than adequately tight tend to work their way out during firing.
If anyone has an explanation, I'm all ears.
Thanks.

[X-Plosive]

Did you happen to modify this gun at all? Maybe the rail?

[BlackVCG]

Hmm... interesting. It sounds to me like you have a tolerance issue of the location of the valve assembly in correlation to the sear. It could be that when you tighten the field strip screw, the valve is too far forward and the sear is not able to pivot up and latch on the bolt because it's not allowing the sear to move up anymore. Therefore, when you loosen the field strip screw, the valve assembly is able to move back just enough that the sear is no longer blocked and the gun charges, hence the click you hear.

If you'll take your field strip screw and thread it in to where it's a couple turns from being tight, push on the back of the valve and watch the gap inbetween the back of the mainbody and the valve. You'll see that there is a bit of play there. In your gun's case, this might be enough shifting of the location of the valve assembly to determine if the gun can shoot or not.

Try this, gas up the gun with the field strip screw loose and see if it can fire. Then fire the gun and hold the trigger. You'll need someone to hold the trigger back. While they're holding the trigger back, push on the back of the valve as hard as you can to take up the gap inbetween it and the mainbody. Then tighen the field strip screw with an allen wrench and then release the trigger. Now see if the gun will fire. If not, then you have a problem with the sear getting blocked with respect to valve assembly location.

Now, before you do any of this, please do make sure that you have the rail spacer installed. If you didn't before, this could be the very cause of your problem. It's a steel roll pin the length of the rear field strip screw hole when the frame and rail are connected. If that isn't in there, get one and your problem will be solved. If it is in there, then go through the things I stated and see if anything changes. This is about all I can think of without seeing the gun. It might be something as stupid as not having the rail spacer, or it might be having parts in the gun out of tolerance. Keep working with it and eliminating variables until you find the problem.

[Maghog]

there is a spacer in the rail, no gap between the body and the valve, ever,and there have been no modifications( I know better than that) I'll still try your suggestions BlackVCG, thanks.