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[krazypaul05]

I've been searching on this forum and i can't find a related topic with a solution.

This topic has been brought up on this thread with one replying post with no solution:

http://www.airsoftretreat.com/forums/index.php?topic=45021.0

Basically, I have the same problem. I have a KSC USP (not the system 7 version but the old) with an upgraded metal slide (prime) and when i take one shot all the gas spews out of the magazine with one trigger pull and i'm out of gas. Is the o-ring the possible culprit? If so, what can i do to fix this problem?

I don't know why this happened. I've been using this pistol with propane gas via propane adapter and this gun was hardly ever abused or fielded,just for some backyard plinking. I hope I can find the solution, thanks for reading. 

[Apotheosis]

Is the o-ring the possible culprit? If so, what can i do to fix this problem?

This definitely sounds like an o-ring problem. I would just replace the o-ring. Sometimes they just degrade slowly even with normal use.

[krazypaul05]

Thanks for the reply. How do I start? Do you think you have a step by step instruction on how to replace the oring. I'm an airsoft noob. Where is the oring exactly?

[Apotheosis]

I do not have personal experience with that particular gun, so I unfortunately cannot provide a step by step guide. Do a little searching. I'm sure it won't be too hard to find some relevant information or at the very least the exploded view of the gun that details each part. A lot of the time the manual that comes with the gun has that in it, so if you've got that lying around, I'd consult that first.

[krazypaul05]

I tried another friend's USP mag and same result. I assume if the oring is on the mag, it must be something with the gun, not the mag. Maybe blowback piston?

[Apotheosis]

That is also possible. It may also be that something is sticking in the trigger mechanism. Make sure the gun is lubricated properly to avoid this.