CZ P-09 random blowback version?
 

I have three green gas mags and three CO2 mags. All six mags I get the same behaviour so I really don't think it's a mag problem. I get completely random levels of blowback and FPS. Everything from really snappy to a little sluggish to wet propane spewing out from under the slide and a bb rolling out the barrel to a complete jam up. When it does jam up its always on the way back and always in the position photographed. Everything I can get to with a field strip (no tools) has been cleaned inspected and lubricated properly. When I manually rack the slide everything feels smooth, there is a SLIGHT resistance in the action when I have an empty mag up against the nozzle and at the point when the nozzle gets pulled away from the inner barrel and back into the blowback housing. I have no problem maintaining my other GBB pistols and GBBR. Gun has performed this way since the beginning. I can go through a whole mag and it works flawlessly and then that same mag another time with same bbs and same full charge of propane will just spew gas and/or barely cycle. Cool down does seem to agravate thr issue like if i shoot burts and for sure if i mag dump. I've scoured multiple airsoft forums and reddit and have a found a few people with the exact same problem but no solves. The thing that stumps me is the complete randomness when no variables (bb type, mag pressure, temoerature, angle when firing etc) change the blowback is just totally unpredictable. I have lots of money in mags so it considering just getting the new version with the tall supressor sights and using this one for parts BUT I'm hesitant, due to this.

Any input is much appreciated.

Its probably a cracked nozzle. Inspect it thoroughly and bend it sligthly, it will probably reveal a crack or gap. If its not the nozzle, check the seal on your piston head and make sure the valve inside the nozzle moves smoothly and that there's nothing stuck in it, but I would put my money on the nozzle.

Disassembled blowback housing and nozzle: Nozzle is sound. Air seal between nozzle and piston head is perfect as far as I can tell. Rocket/floating valve functions fine manually. Took nozzle apart. O ring is good on the rocket valve and it seals properly when closed (blow tested compression on the rocket valve and piston head). There was a little rust and corrosion on part of the rocket valve spring I cleaned that and lightly oiled it as well as the o-ring. Cut two coils off the recoil spring as it is wicked stiff thought maybe gas pressure had trouble overcoming it. Now I reassembled and tested it still has random blowback strength performance hasn't appeared to change or maybe a very slight improvement as it hasn't actually jammed up again. Maybe I'll get into the hammer/valve knocker next.

Inspect the seal between the nozzle and the mags. Are the magazines sitting too low? It might be a magazine catch issue. They might also be sitting too high, but that's rarer. Try to push the magazine up with your hand while firing and see if its better or worse. Does the magazine have any play in the magwell?

Another possibility is that there is something impeding the movement of the valve knocker. Or one of the parts linking to the valve knocker is damaged.

Aha. There appears to be some random variation in the amount of force it takes to push the hammer backwards. Especially at the point in the action where it sometimes jams (very early in the cycle). Mag port to bottom of nozzle connection is good. I keep cocking the hammer while watching it with slide off and I can't see why sometimes it pushes back easily and sometimes it seems to snag and be difficult to push back. Some of the parts seem to have some play. I've never disassembled this part before so next time I get an hour of bench time I guess I'll learn some things. Or irreversibly ef It up. Thanks for your help.

Hmm. It might be a broken hammer spring on some crap is lodged in there. Are you testing the hammer only or moving the whole frame? Not sure how the P09 is made, but there's also the two prongs that reset the valve knocker and mechanism, do these jam too or do they work smoothly? Anyway, you know the problem is in the action now.

Fully disassembled the lower. Deburred, cleaned and lubricated each part. Checked action of each part for function. Discovered the cause in the variation in resistance of the double action. The trigger bar when re-engaging the disconnector: sometimes it lands high on the disconnector which makes the double action pushing the hammer back really stiff, sometimes it finds a lower position on the disconnector and the action is really smooth. However this problem is unrelated to the weak blow back as when the blowback is pushing the slide back and cocking the hammer, the trigger bar is not involved and isn't causing any resistance to the blowback action. Reassembled and problem is more consistent. My symptoms are textbook rocket valve but rocket valve is 100 percent. I've spent too many hours on this cheap gun. Love the ergonomics but this last inspection revealed it's pretty poorly made on the inside. Parts are really roughly cast and tolerances are sloppy. Time to go back to a more common/proven platform that actually has aftermarket parts available. Good bye P-09.

Keep on it, I've got one that I've been doing a handfull of crazy things to. There's nothing aftermarket for it, so I've introduced it to my mill :)

on mine, the rocket valve o-ring got chewed up.

If you email KJW from their website, you can order individual parts and it barely costs anything.

This is old now. This almost too embarrassing to post. The hop up was set to high, bbs were just barely too hard to push past the hop up. Turned hop off and works flawlessly. Head buried in hands... lol

Thanks for your help.

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