Was recommended that I post this here as I might get more help with my issue.

So I bought a full size USP9 as a can host. Not the SD model, just a base model and threw a factory threaded barrel in it.

Will not cycle with the can on and running 147gr subs. As in the slide doesn't cycle at all, just a single shot at the moment. Now if I take the can off it cycles the subs perfectly, so it's not an ammo problem I wouldn't think.

I did not try to run supers through the can, I'm following up and trying that on Friday.

Can is a Osprey 40 can running a 9mm piston.

Some have said throw the SD recoil spring assembly in it as it is beefed up for suppressor work, but I don't see a beefier spring setup helping the fact that it is not cycling at all. I could see if it was cycling too fast due to the extra pressure, but that isn't the case. Also I hate to throw another $100 at this rig if it just isn't going to run, already deep in it with the price of the gun, sights, barrel and extra mags.

If you pull on the can while it is mounted on the pistol, does the piston move smoothly? Just want to make sure your LID is working properly and not binding.

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Actually yes it is very "sticky" and binding up a bit.

I'm gonna take the can apart and clean it up real good, giving it another shot tomorrow.

Please let us know how it goes.

I would check the o-ring in the spring retainer to makes sure it is seated properly and also not chewed up or torn.

Use a light layer of grease or some CLP to lube the piston.


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O-ring came apart, that's what was causing the binding. Found some replacements on Amazon for pretty cheap, gonna get them on the way. Thanks for all the help I will definitely keep this thread updated.

There's a reason why that dude's an engineer!

 
Don't go too cheap - make sure you get Viton o-rings. Others aren't so chemical resistant and may swell in the presence of oils/greases and lead to the same problem.

Alas, just a design engineer in a medical device company ... how does the saying go - "takes one to know one"?



 

Ok so here is what we learned today....

The gun ran much better than before after replacing the o-ring and making sure everything was cleaned well. But it still has its issues....
With the subs and can it's having 3-5 stovepipes per mag now, which is a huge upgrade from the single shot it was before!

Ejection pattern is somewhat erratic, except for when it goes into one of its "good strings".

It runs 100% with the can and supersonic rounds. Ran 100 rounds through this way and zero malfunctions.

It did actually get one mag of subs to run 100%, dunno why it won't maintain that.

What brand of ammo are you using?

Primarily been running Freedom Munition 147gr for the subs, and just basic federal 115gr for the supers.

Can you provide link to O rings on Amazon?  good to have a few spares.  I have a Ti Rant 9 with no idea of size of O rings.

Too true bro!

On the USP9, I'm more familiar with the 45, but it's one of the hardest to get running.  I'd recommend getting the buffer unless you can really see that it's not fully cycling.  In that case, I'd try getting in touch with HK.  It could just be the barrel fitup with the slide.  Any wear marks at the locking points?

 
http://www.advanced-armament.com/assets/images/pdf/manuals/O-Ring_Guide.pdf

http://www.amazon.com/gp/product/B0051Y1U0Y/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1