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USP slide not locking back after firing the last round

USP slide not locking

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#1 crater.manic@gmail.com

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Posted 24 April 2013 - 07:58 AM

Dear All,

I've already read:

http://kwausa.com/fo...topic=7024  and
http://kwausa.com/fo...ck&fromsearch=1

I own a Full-size ("Regular"), a Tactical and a Match. I use the Regular as my main weapon for CQB and sidearm for outdoors.The Tactical and Match are primarily for collection. I've in total 8 mags, 4 Regular, three Match, one Tactical. I use 4 Regular mags and one Match mag routinely. The other three are still boxed.

Towards the end of 2012, I was troubled by the slide of the Regular not locking back after the last round was fired with all the 5 mags I regularly use ("worn mags").

I tried to fire an "out of the box" Match mag with one round loaded, the slide locked back okay.

Cupping the bottom of a worn mag would also result in the slide locking back after shooting the last round. However, having to push against the bottom of the mag is not natural. I've noticed free-play with the worn mags as well.

I tried firing a worn mag with the Tactical with one round loaded and resulted in the slide not locking back, as experienced with the Regular.

The experimental evidence pointed towards that the problem is vested with the mag and not with my Regular USP. Judging from the free-play, either one or both the mag-catch in the gun and the latching surface of the worn mags have been worn down. As a result, there is inadequate sealing between the rubber gas exit port of the mag and the gas input port of the loading nozzle

I tried soaking for one week the rubber gas exit port of one of the worn mags in #20 pure silicon oil for remote control cars shock absorbers. That didn't not swell up the rubber to provide a better seal.

With the large gas reservoir, the NS2 USP mags worked great and provided stable propulsion until the above problem surfaced.

Anyone has any solution to this problem?

Best regards,

Edited by crater.manic@gmail.com, 24 April 2013 - 08:53 AM.


#2 gcw360

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Posted 24 April 2013 - 04:37 PM

Or maybe the BB follower is damaged?  Can you post a picture of the front of the follower released to the top of the mag and the left side of the top of the mag?

#3 muffinman1604

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Posted 24 April 2013 - 04:39 PM

Take a look at your mag catch on your gun. And how "worn" are the mags? any pictures? Any parts on them broken or damaged in any way?

Edited by muffinman1604, 24 April 2013 - 04:40 PM.


#4 crater.manic@gmail.com

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Posted 24 April 2013 - 09:13 PM

[attachment=1217:IMG_3602.jpg]The followers should be in good working order. I tried racking the slide with each of the worn mags when they are empty. The slide locked back without issue. Please refer to the photo.

Photo removed due to the 500k limit.

Edited by crater.manic@gmail.com, 29 April 2013 - 08:36 AM.


#5 crater.manic@gmail.com

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Posted 24 April 2013 - 09:37 PM

Photo of close up follower push-rod.
[attachment=1218:IMG_3604.jpg]

Photo removed due to the 500k limit.

Edited by crater.manic@gmail.com, 29 April 2013 - 08:36 AM.


#6 crater.manic@gmail.com

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Posted 24 April 2013 - 09:39 PM

[attachment=1219:IMG_3608.jpg]

Photo of the latch surfaces of the worn mags.

The wear might just be fractions of a millimetre and hard to tell by sight. However, enough to affect the slide locking.

I don't think I want to remove the mag-catch from the gun for inspection. Please note the "last round slide locking" was working fine when I test with a nearly new mag.

Photo removed due to the 500k limit.

Edited by crater.manic@gmail.com, 29 April 2013 - 08:38 AM.


#7 Frankie9011

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Posted 25 April 2013 - 01:01 AM

I'm having the exact same issue.. although I only have one mag to test it in, and the slide refuses to lock back on the last round. My mags look identical to yours. No visible wear on the follower.

Only had the gun for a week, as well.

#8 crater.manic@gmail.com

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Posted 29 April 2013 - 08:56 AM

Problem seems to be down to the seal between the mags' gas exit ports and the loading nozzle due to worn latching surface on the mags. This is bad news as the MP7 is of a similar design. I'm already getting problems with one of my MP7 mags. The blow back doesn't seem to be going far back enough to scoop up a bb from the mag, due to bad sealing.

#9 Kerberos

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Posted 10 September 2013 - 02:56 PM

Another thing to add is also the worn down slide as well. Common on the USP MK23 and some USP variants, the slide catch tends to wear down to an angle and that also prevents the slide from naturally locking back. Of course with an empty magazine inserted and you pull the slide back, it is possible to engage the slide catch to some degree, but you cannot expect that to happen with a gas loaded magazine. You can either try sharpen the slide catch groove to be 90 degree perpendicular to the slide or buy a new slide set. Sometimes these things are a combination of everything.

#10 RogueSpartan7

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Posted 17 November 2013 - 09:22 PM

I'm having this problem too. I was literally about to throw the pistol out the window because of all of the problems i've had with it, but it's a relatively easy fix:

Check the magazine and magazine release, my mag sits too low for the firing pin so when the hammer strikes the pin, and the pin strikes the release, there isn't enough gas being pushed out into the gun to make full cycle.

Now you can either:

Make the firing pin larger...

Or

Buy a new magazine release from the pro shop.

To refrain from this issue later, I recommend letting your mags fall out and catching them with your hand. Try not to grab and pull the mag before hitting the release.

Hope this helped!




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