Issues with HK45 mag release on USP 40

[TheTrevor]

After seeing all the cool kids switching their HK pistols over to the extended mag release from the HK45, I decided to install one on my USP. In dry-fire testing it was great, and I really loved the extra surface area to index onto when dropping a mag.

However, when I took it to the range, I started running into issues with the magazine popping loose during live fire. After the first trip, I thought it was because mag #01 was my oldest and perhaps the retention lip was a bit rounded over or worn. The next range trip a week later was for a 1:1 instruction session with a new shooter -- and the drop-free-during-fire plague had evidently spread to several more magazines, and of course it manifested when I was shooting a demonstration. Needless to say I did not turn in my tightest groups ever when every shot had me wondering if the mag would stay locked into place.

When I compared the original USP mag release side-by-side with the HK45 mag release (which I should have done before installing my shiny new upgrade) it was immediately obvious that the HK45 unit's latch is about half the width of the USP's.

Just to complicate things, I may have neglected to swap in the apparently stiffer spring which came with the HK45 unit.

Is the narrow-latch HK45 mag release known to work well in the USP 9/40 chassis when used in conjunction with polymer magazines?

If so, is the likely cause of failure the first time around that I forgot to swap in the stronger mag-release spring?

I'm back on the original USP latch now, but if the spring is the likely culprit I'm willing to give this another try.

[BigT]

I fitted one of these to my USP9 and a buddy fitted them to both of his.

After 5k rounds with zero issue mine started dumping mags from time to time. His harder use USP with a similar round count has also started. Even worse than mine.

[gtmtnbiker98]

You are talking about the HK45 Compact mag release, right?

[TheTrevor]

You are talking about the HK45 Compact mag release, right?

Yep.

http://www.hkparts.net/shop/pc/Exten...s-265p1669.htm

I fitted one of these to my USP9 and a buddy fitted them to both of his.

After 5k rounds with zero issue mine started dumping mags from time to time. His harder use USP with a similar round count has also started. Even worse than mine.

Thanks for confirming that it's not just me. You might try swapping out just the spring before going back to the standard USP mag release.

I think I may have seen the issue more quickly due to the higher recoil impulse forces of the 40.

[BigT]

We put new spring in when we fitted the part. May explain why the lasted this long.

[TheTrevor]

We put new spring in when we fitted the part. May explain why the lasted this long.

HKparts has mag release springs for $4 each. Might be worth a try.

http://www.hkparts.net/shop/pc/Magaz...s-265p1814.htm

ETA: Whoops, just saw that you're in SA. Yeah, postage from the US to SA is going to be more than the cost of the springs. Maybe the HK rep for SA can hook you up with some springs?

[LSP972]

There are issues when using the HK45C mag release on the USPf. IIRC, it has to do with the geometry of the part… although the polymer magazines might be part of the equation, I simply do not remember. There was a thread regarding this on HKPro that detailed the "fix"; you might try over there. I'll have a look there a bit later if you have no luck.

OTOH, this part is a drop-in fit on the USPc and P2000/P2000SK. It really makes a difference too.

.

[TheTrevor]

There are issues when using the HK45C mag release on the USPf. IIRC, it has to do with the geometry of the part… although the polymer magazines might be part of the equation, I simply do not remember. There was a thread regarding this on HKPro that detailed the "fix"; you might try over there. I'll have a look there a bit later if you have no luck.

OTOH, this part is a drop-in fit on the USPc and P2000/P2000SK. It really makes a difference too.

It's funny -- if I don't know whether there's a solution to a problem, I give up a lot sooner than if someone says "look over on forum X, somebody over there figured it out" even if that means a fair bit of digging. Found it!

http://www.hkpro.com/forum/hk-handgu...ease-work.html

Looks like the HK45c release needs the tip re-contoured and a lip on the body reduced for clearance. I'll be giving the described mods a try tonight, and hopefully I'll get my ammo shipment on Monday so I can try it out.

Thanks, LSP972!

[BigBoss0311]

After dryfiring and reloading quite a bit with the HK45 (extended mag) release on my USP 40 Tactical I decided to stick with the original. No, the original does not feel as good, but it works EVERY time. There is nothing more I ask for from my pistols than this. The original still works and gets the job done when I need it to, the extended mag release feels better doing it, but less reliably on the 40 than I'd like. So i don't use it.

[TheTrevor]

Just to follow up on this...

I did some digging on HKpro as LSP972 suggested, and came up with sufficient clues that I felt I had a handle on what needed to be modified on the HK45 mag release to make it work happily on a USP.

Using a 3/4-inch diameter sanding drum on a Dremel, I carefully recontoured the plastic molding near the projecting metal tab which actually engages the magazine. I removed a bit of material at a time until the contour was similar to the stock USP mag release. (This was non-obvious and I may have never figured out this one on my own.)

The metal tab turned out to be harder, quite literally -- it's made of hardened steel which laughed at my attempts to file it. Lucky for me I have a metalworking shop at home, including an 8-inch pedestal grinder set up to grind hardened steel. Looking at the tab from the side, I needed to grind a bit off of the upper and lower edges of the tip at roughly a 45-60 degree angle so that the tip would engage properly with the polymer magazine catch recess. It took longer to mark the areas to grind away and fire up the grinder than it did to do the actual grinding.

With the excess material removed, the mag release performed brilliantly in competition last Saturday. Mags leapt out of the magwell when I wanted them to, and stayed in securely the rest of the time.

Verdict: Highly recommended upgrade for the USP but ONLY if you have access to a grinder with a soft wheel suitable for hardened steel. It *might* be possible to evenly grind the edge of the metal tip with a Dremel or similar, but I think that's a bad idea that could lead to random magazine ejection during live fire.