Semi auto then full auto on full auto

[manaman]

Having a weird selector issue with a G&P Zombie Killer CQB-R here:

Safe and semi auto function fine. When the gun has been fired in semi auto, then the selector moved to full auto, the gun will fire one round (like semi auto). Releasing the trigger and pulling again, we get full auto. From there, pulling the trigger continues to give normal full auto.

When full auto is working and the selector is moved back to semi, then back to full auto, the gun continues to fire in full auto.

It seems to consistently fire a single semi auto shot before firing in full auto only after the gun has been cycled at least once in semi auto.

Any ideas? The selector switch and plate seem fine, but I can't think of what could be going on inside to produce this problem with such repeatable consistency (literally every time).

[ThunderCactus]

I had the same problem on a G&P I worked on, cannot remember for the life of me how I fixed it lol
How stiff is the selector plate?
How stiff is the cutoff lever?
How's the spring on your cutoff lever?

[tunabreath]

Selector plate moves freely. I didn't check the cutoff lever directly, but it seems to be actuated appropriately by the selector plate/spring.

I did have one issue when installing the trigger - the trigger spring on the G&P has 2 right angle bends, one on the trigger side and one on the mechbox side. Most trigger springs that I've seen are straight on the mechbox side. Additionally, there didn't appear to be anywhere for the bent end on the mechbox side to be inserted (the plate on the switch body fills up that entire area), so the trigger was very prone to jumping out while reassembling.

I think it's unlikely because the trigger itself is held quite rigidly about its pivot points by the mechbox shell, but do you think the sideways force on the trigger could be affecting its engagement with the switch shuttle? Maybe the force exerted on the switch body by the end of the spring? (the switch body is securely screwed to the mechbox shell though...)

*edit, whoop, posted from my friend's house/account yesterday :P

[audi_bhoy]

Most likely the selector plate is partially blocked by the cut-off lever when firing in semi, and it completes its way on to full auto after the first shot on full auto, AFAIK...

[tunabreath]

Hmm, I'm having a tough time imagining the selector plate binding because the selector switch moves freely and with uniform pressure between each position. Maybe the back end of the plate is flexing out so that I can't feel the front end being hung up on the cut off lever...

I'll take a closer look next time I have my hands on the gun - will do some testing with just the mechbox and grip/motor outside of the receiver so that I can see the cutoff and entire selector plate while it cycles.

[ThunderCactus]

G&P springs are like that, I cut the mechbox side angle short, but I think there's a small hole it's actually supposed to fit into....