Continued below. Had to do it this way to update the link to Big Bore's LEM Trigger Job.
Can I get a USP in 10mm? If you don't mind butchering a USP40, contact MBSL for more info.
I want to mount a scope to my USP, is there a scope mount? Yes, HK DID make a scope mount. You can find them on E-bay once in a while. If you use a adjustable rear sight, you might not be able to use the scope mount because the mount will interfere the rear sight. Another option is to use a Doctor, Optima, or JPoint sight which you can purchase a mount that goes on the rear sight dovetail.
I want to get a lighter trigger pull, can I replace the hammer spring? Yes you can go with a lighter hammer spring available from Wolff Springs http://www.gunsprings.com You will get a lighter pull by using a lighter spring, however on some guns will you end up getting light primer strikes. You have to have a lighter pull, considering using Federal primers as they have a softer cup.
Does the o-ring work? CCFA says yes. Bruce Gray says no. Bruce Gray did extensive testing and development with the USP series. He cut some o-ring grooves into the barrels and didn't see and improvement. He ran Expert barrels cut for o-ring but without the o-ring and didn't see any changes either. So who knows.
How good are Bruce Gray's trigger jobs? He can make them much better than stock. He can do a simple polishing to smooth everything up. If you are an experienced competition shooter, he can rework the USP trigger down to 2 lbs with minimal over travel and minimal reset, but it does void the warranty and disables double action and the firing pin block, as I said for experience competition shooters only. It is as good as a decent 1911 trigger.
Are Promag good mags? NO. All they are good for is a paper weight.
My extractor color looks funny, is there something wrong? This is normal. Some extractors will look purple. The hardness of the steel sometimes does not take blueing well.
How do you color the lettering red or white? Use china markers or paint. Cover the letters and wipe off the excess.
When I decock, does the hammer hit the firing pin? Yes and no. On the first generation USP, there is no half cock. So when you decock, the hammer does hit the firing pin, but the firing pin block prevents the firing pin from contacting the primer. On later guns, when you decock, the hammer is released to the half cock position.
There's a lot of play between the slide and the frame, how can I fix it? You can't. Repeat after me, "It's not a 1911." 1911 are often handfitted and will have a tight but smooth slide to frame fit. USP is a mass produced gun. Tolerances between parts are design to be loose which aids in production. Loose fit is sometimes more reliable also.
Can I buy conversion kits in the US? No, if you can, it will cost as much as a new gun.
I can't reach the mag release with my thumb, help? Use your trigger finger or middle finger.
When I do a field strip, the pin above the safety is shifted, is this a problem? The pin will move sometimes. Just push it back before you reinstall the slide.
Is it safe to drop the hammer with the slide off? No, don't do it. You are causing excessive wear and tear.
Are the trigger in the Match, Tactical, Expert, and Elite the same? Yes, but do to variations in production, you will get slightly different pulls on each of them.
Where can I get a USP in 357 Sig? 357 Sig is a necked down 40 S&W. USPc40 can be converted to 357 Sig with a barrel change. Fullsize guns have experienced feed problems with a barrel swap.
What are the solutions to fix accidental decocking when riding the safety? There are 3 things you can do to prevent accidental decocking when riding the safety. One, change to V9 or V10, but you lose decocking capabilities. Two, install an ambidextrous safety. The safety lever on the other side will hit your hand preventing you from decocking while firing. If you need to decock, you will have to shift your hand slight. Three, modify the detent plate. If you look at how the detent plate works, by carefully filing the ramp so it is more vertical, it will get harder to decock. If you take off too much, it won't decock at all.
How do you lighten the LEM trigger? Here's is Big Bore's write up on doing a LEM trigger job.
How should you grip a gun? Here are a couple links on what is the best way to grip a gun.
Lost the dot on the sights? This has happen on the USP, but guess HK can't seem to get it right for the last 3 decades. P7's have been having this problem for a long time. The rod can be super glued back in. If you lose the rod, you can fill the hole with paint.
Why are some P7 plum colored? The P7 metal is incredibly hard and very difficult to blue. The plum color is basically a bad bluing job. Even if you get it reblued, the back of the slide will often be a different color.