KSC G18C vents all gas on first shot. Replaced many parts - need advice please.

[puppydg68]

The Original Problem: Gun stopped working in Full-Auto Mode. Gun would fire one round, and then vent all gas out of the magazine, slide would be half cocked and usually the Fire Selector switch was in the middle position instead of the auto position. Semi-Auto was fine. Worked great for the longest time Semi-Auto only.

Now: Gun will vent gas after the first few shots on any mode. Single or Auto.
I've read all over the place, and followed many different suggestions, i've gone and replaced many parts to no success.

What I tried:
I noticed that the cylnder piece(Part #22) was a little chipped away, and I thought it was the problem, so i purchased a new one and replaced it (Part #22) I also replaced the valve with a rocket valve(Part #24) and the 2 springs(Part #23) that hold part #22. Its still happening.

So I suspect its something else. So I removed the inner and outerbarrel. and started sliding the slide back and forth to see where it's getting stuck. As I move the slide backwards, i hit resistance half an inch backwards from the normal position. This seems to be where the Part 251 rolls over part #253. It takes some effort to push the slide past that point. Sometimes its harder than others. I don't know if this is normal.

So at this point I can't seem to get the gun to fire on auto at all. one shot, vents all and the selector switch resets to the middle possition. On Semi-Auto It will vent all at some point through the magazine, usually first round.

One thing i noticed with my replacement part #22. the cylnder seems to not go all the way to the back all the time as it feels like the inside of the cylynder is a little tighter to the rubber piece #27 than the original part 22. Maybe resulting in a lower power on the shots that do come out. I also noticed that the part #22 doesn't seem to slide as well when i pull it and it snaps back to resting position. However regarless of this either the original or replacement Part #22 the gun exhibits the same behaviour.

I've also tightened any screws, philips or set screws. I've replaced recoil spring/guide, part 10 on the inner barrel, and the inner barrel. Every where i read, a different part was suggested to fix the problem, but no-one with an actual definative solution.

Thanks for reading, i really hope you are able to help me out. I'm fairly new to airsoft and i have been trying to fix this gun for a couple months now. I've spent a lot of money on replacement parts and I can't figure it out. I bought an entire spring replacement kit in addition the other parts mentioned above.

[Dishonest Abe]

Have you tested other mags to see if it is a fluke problem? Because for some odd reason, this happened to one of my friend's GBB pistol, and it ended up being the mag.

[puppydg68]

Hello there thanks for you input, unforunately yes i tested 3 different mags

[Ross]

Have you tried silicone oil? Kinda obvious, but I've heard of people missing this step.

[supramk3]

could it be the firing pin or along the lines? happened to my p226 in which when i pressed on the trigger nothing would happen when the gun was suppose to shoot, took EVERYTHING apart, inspected it, lubed it, found out it was a spring problem (iirc) put it back and repalced it, and never happened again.

[Kos-Mos]

What rocket valve did you buy?

I ran into a similar issue while replacing a broken valve with the airsoft surgeon one.

The return spring was too stiff and it was designed to be used only with high flow valves.

The original spring was bent crazy... I found a working spring in a push-pen.

[puppydg68]

Originally Posted by Kos-Mos

What rocket valve did you buy?

I ran into a similar issue while replacing a broken valve with the airsoft surgeon one.

The return spring was too stiff and it was designed to be used only with high flow valves.

The original spring was bent crazy... I found a working spring in a push-pen.

Shooters Design. but i only bought that because i thought it might fix it.. None of my replacement parts made a difference, i feel like I'm missing something.

it almost feels like the slide is getting stuck. When I pull the slide back manually at the point where the open "square" part of the innerbarrel on the top of the glock goes underneath the outerbarrel it feels a little stiff, is that normal?

[puppydg68]

Originally Posted by Ross

Have you tried silicone oil? Kinda obvious, but I've heard of people missing this step.

Yeah, i've tried a lot of oil unfortunately

[Kos-Mos]

Might be time to bring it to a gun doc then... there is very little we can do by forums, especially with no pictures or high-res video...