KJW M4 GBB V3 Gas and feeding issue

[Scryden]

Hi all,

I have a little issue with my KJ Works M4 GBB V3 rifle. I purchased the rifle a little over a month ago, so practically still brand new. I played with it for a solid month without any issue whatsoever. After a month I decided to do some basic maintenance on it like cleaning and regreasing the bolt, trigger etc (pretty much all metal to metal moving parts). I used pure silicone oil on the O-ring and Superlube synthethic grease on all metal to metal parts.

Ever since I took it apart for a clean and regrease, I am having issues with it. The biggest issue is that its not consistent, so for the folks in the store where I bought it its hard to troubleshoot.

I can play with the rifle for hours straight, but sometimes 2 BBs are fed at the same time as I am shooting and it jams. Have to take out the mag, shake out the redundant BB, put the mag back in and continue playing. It has never done that before I took it apart.
Second issue is gas related and doesn't show up until after a few hours of play. At some point during a night of play I can fill up my mags with gas and BBs but after firing only 3 or 4 shots, the mag is completely out of gas already. All 3 of my mags have this issue at the same time so I think its an issue with the rifle itself. I thought that maybe the nozzle gets frozen, so I put it away for half an hour and then picked it up again. Still the same issue, so I have to leave early from the field because I can't play with it anymore.
I brought it into the shop the next day and then of course, the issue magically disappeared. They did do another clean and regrease in the shop and tested it. Shot 2 full mags full auto and no problems. The very next night I started playing on the field again, after a few hours the issue returned.
Maybe important to add: when the issue is there and I fire a round, I see gas coming out of the chamber, as if it is feeding way too much gas for 1 shot.

I don't really know what else to do right now. The guys at the CQB field have no clue. The guys in the shop have no clue and the issue isn't there when I bring it in (only happens after a few hours of play). I doubt its related to parts freezing up because even after 30 minutes of putting it away, the issue is still there.

Any advice or tips are greatly appreciated. Such a shame it happens on a practically still brand new gun.

[RainyEyes]

Assuming the store techs were competent and I'm fairly certain they were this is just a case of magazine cool down... Your store reps did tell you this was a thing, right?

If the mags get too cold gas doesn't expand after too much shooting, Blah blah blah.

Tl;Dr your gun is fine just find a way to warm up your mags after each game.

[Scryden]

Originally Posted by RainyEyes

Assuming the store techs were competent and I'm fairly certain they were this is just a case of magazine cool down... Your store reps did tell you this was a thing, right?

If the mags get too cold gas doesn't expand after too much shooting, Blah blah blah.

Tl;Dr your gun is fine just find a way to warm up your mags after each game.

I have to add that I am not a trigger happy player. Most games I don't even reload once and at the end of the round I fill up the same mag again as I was using. So, especially for my third magazine, that one usually doesn't get used at all during a game night, yet it has the same issue at the same time as my other two mags.

[Scryden]

So I just came home from a night of airsoft and had the exact same issue again. I had not played in over 2 weeks and before I went on the field I even warmed up my mags. During the very first round I was able to fire 3 shots before I was completely out of gas already. Tried my second mag. 3 shots, dead. Tried my third mag. 3 shots, dead.
Thought maybe an issue with the nozzle so I replaced the entire bolt carrier group as I had a spare with me. Filled up all 3 mags with gas, tried again, same issue. So either all my mags magically broke at the same time or there is something wrong with the rifle.

Any hints are greatly appreciated.

[Red62]

take video of yourself doing the maintenance. Post it on Youtube and then post it here again: you may have contaminated something with either the wrong grease/oil or put something out of alignment

[RainyEyes]

Assuming neither nozzles are broken, there are probably a few possibilities:

The valve inside the nozzle is defective
The piston is leaking/broken
Recoil spring too strong

[BioRage]

Problem 1:

I would bet my money on a swollen bucking. - Replace it with a new one and avoid any oil/grease to get into it.

Problem 2:

Does your magazines get super cold after a while?

[RainyEyes]

Originally Posted by BioRage

Problem 1:

I would bet my money on a swollen bucking. - Replace it with a new one and avoid any oil/grease to get into it.

Problem 2:

Does your magazines get super cold after a while?

That was my initial suspicion as well. But if the bb doesn't feed it should prevent the gun from feeding rather than spewing all the gas.

My px4 can catch and hold the bb and still cycle 20+ shots with the bb dropping out after each shot because it's holding onto the bb. I assume it's the same for the gbbr.

[Scryden]

Problem has been resolved.

I took the rifle to a different shop this time and it appears that the store where I got the green gas from sold me the wrong type of gas. It was low PSI gas meant for low fps pistols. So once the pressure in the magazines equalized with the can, there was still barely any gas in the magazines.
The guy in the store tried their own green gas after and he was able to shoot almost 2 and a half full magazines of BBs with it.
He found out about it being the wrong gas by reading the small letters on the back of the canister. When I bought the canister, I mentioned I was looking for green gas for my M4 gbb, so he must've accidentally sold me the wrong one.

Anyway, I am glad this is resolved so now I can get back to playing.

Thanks all for the help.