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USP Compact OLD VERSION- BBs falling out/ shot at 2 meters... sometimes, more... unpredictable.


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#1 Aussiephoenix

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Posted 03 October 2012 - 02:04 PM

Hi guys, first post here, by need unfortunately...

I got an USP Compact  (OLD VERSION)- The mag is leaking, but i know how to fix that, however it still holds a fair amount of gas, enough to cycle the slide with plenty of force... on the other end, however is where the problem lies, as the bbs fly out, and almost instantly drop. Im talking about 2meters or so... can anyone give me some pointers on what to look for? (Im fairly handy, though not an expert, lol. meaning I'm used to basic GBB maintenance, etc)

I was trying the gun out in the garage yesterday, took the hop apart, everything looks functional (though how that hop up actually works, is something I dont really understand. I'd gladly accept some insight nto this...the MK23 hop is easy to understand...) I fired off about 3 mags and made the following deductions... on a fully loaded mag, it usually fires off half the mag properly, then, it starts shooting "blanks" and when I tip the gun down after the shot, the bb rolls out of the barrel. Also, once, during cicling, a BB comes flying out from the top of the gun as if a spent shell...!? (oh, its not lack of gas, though the mag has seen better days. even after those inicial shots where it goes well, just when it starts shooting blanks, I pulled out the mag and vented the remaining gas... it was quite a lot...)

Any help/pointers would be welcome.
Thanks in advance.

Edited by Aussiephoenix, 10 October 2012 - 09:20 AM.


#2 gcw360

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Posted 03 October 2012 - 02:37 PM

Hi AP - Welcome to the KWA Forums.  Since these are really "help" forums, you are in the right place!  I gather this is a used/secondhand gun...is this true?  Are you using green gas or propane? And, if the gun is used, do you know if the gun was fire on propane or green gas?  The reason I ask is that with propane you need to add silicone.  Adding too much can cause the bucking to swell which can cause misfires.  That said, are BB's getting stuck in the barrel at the hop-up or is the gun simply not firing BB's?  Lets determine that and then we can get moving towards a resolution.

If the gun is just simply not loading the BB's, then I am guessing the cylinder needs replacing...

#3 Aussiephoenix

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Posted 04 October 2012 - 02:53 AM

Yes, I bought this gun second hand, and I really dont know what the previous owner was using on it, but the most common out here is normal green gas, which is what I use too.

I took the hop/barrel apart, and it doesnt "look" swolen, though it wasnt exactly dry either... It looks about the same size as the other replacement hop rubbers I have for my TM mk23 (except without the little rubber tab, and with a little "hole" which doesnt go all the way through).

I guess I need to know how this hop up unit is supposed to work, as while putting it back together, I cant really see what diference twisting the dented wheel one way or the other would have on the hop... also, I'm not sure the hop is mounted properly, anyone have a simple diagram they can share?

#4 Aussiephoenix

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Posted 04 October 2012 - 02:58 AM

The BBs arent getting stuck, they just dont seem to have the needed compression to exit (most - times) like I mentioned in the first post. usually on a freshly packed mag I can get off a few NORMAL shots. cant really figure out what would be causing this...

thought something might be wrong with the mag spring, but it seems strong enough... and the bbs are getting into the hop chamber...

one thing I noticed, dont know if its relevant or not, the metal nozzle has a smaller diameter tube at the front which moves in and out on a spring (I assume) if I push it in with my finger, it comes back out very slugishly... should it be faster? could this be what is causing the lack of compression in not closing the chamber properly?

thanks

#5 Aussiephoenix

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Posted 10 October 2012 - 09:23 AM

Hey guys, does anyone know where I can get a detailed blow up diagram of the old version?

or...
a detailed tutorial a full disassembly of the slide.

Needs to be the non System7/NS2 though.

#6 Viet

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Posted 10 October 2012 - 09:48 AM

http://kwausa.com/fi...kp8_non_ns2.jpg

#7 Aussiephoenix

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Posted 10 October 2012 - 09:55 AM

Thanks Viet!

Also... how does this hop up really work?
Never seen one like this...

I think I found the problem straight out... On disassembling the hop up unit, I didnt find a ballbearing (part 19) anyone know what size they are?




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