The O-ring engagement was among a few of HK's innovations with the USP line of pistols. They claim it provides better accuracy by allowing the barrel to fully lock up with the slide. There is some debate to the validity of the claim, but nonetheless, only a select number of models were fitted with an O-ring barrel.

The following models were delivered from the factory with an O-ring barrel:

• Mark 23
• USP Tactical 40/45 + Compact (Not the USP-SD)
• USP Match
• USP Expert
• USP Elite
• HK 45 + Compact

So the standard USP does not have an O-ring barrel. Which makes perfect sense because the barrel does not protrude enough past the slide for an O-ring. However, the USP-SD has plenty of barrel length yet does not have the O-ring like it's bigger brothers (the .40 and .45). Is it possible to add an O-ring a USP-SD barrel? You would think so right?

Well the answer is no, and here is why; HK barrels are hammer forged. Once they are forged they are then cooled to a temperature that makes them even more resistant to wear. Once completely cooled the metal is so hard it cannot be cut or threaded as the barrel will break any tools used to do so. It's like trying to cut a diamond with a hack saw. This why you really do not need thread protectors for the tactical barrels. Due to the hardness, if you ever manage to cross-thread your suppressor with an HK barrel, the suppressor mount would be re-threaded. Not the barrel.

If you are after a custom barrel for your USP with an O-ring engagement, check out Jarvis barrels. They are high quality, match grade products that drop right into HK pistols with no problems. They produce a variety of barrels with different lengths and features.