Howdy!  A HK USP .40 was my first *real* (read: capable of putting decent sized holes in a badguy) handgun, and I love it!  However, What sort of stuff can I do to beef it up?  Specifically - I'm a dummy when it comes to barrels.  What sorts of things would I need to look at/know to get a better barrel than the standard factory one?  Like, making it more accurate without compromising ANY on reliability/durability is what I'm after.  Also, I've heard of some people complaining about the polygonal profile - why?

Second question: what are your favorite tac lights for a USP full size?  I know that with the kind of rail it uses, there's less out there for the USP than for others.

Third Question: What kind of sights could I get that would be good for low-light defensive use?  What do you all use?

Final question: What kind of .40S&W round do you all use for defense?  I just plink/target shoot with 165 or 180 gr Winchester FMJ, but I'd like to buy about 20 or 50 rounds of some good stuff to leave in a magazine.  

Just wantin' to get a wide range of opinions, as I don't know much about anything besides puttin' holes on paper.  Thanks!

Leave the barrel alone.  Some people don't like polygonal rifling because its hazardous to shoot cast lead bullets from such barrels.  A barrel from a USP Tac .40 would be a good upgrade, but I would spend the money elsewhere.  Insight M2 or HK UTL for the light.  I use 165 Speer GoldDot hollowpoints in my Sig.

Allllllrighty.

As far as barrels...HK makes some of the best pistol barrels in the world.  Only one better for that platform would be an HK USP .40 Tactical barrel.  Even then, its not worth it.  You'll be hard pressed to become a better shot than your USP barrel.

As for lights, I love my Streamlight M2.  Identical to the HK UTL.  Other options would be the GGG slimline adapter, and your light of choice.

I'm not a huge fan of night sights.  I'll never shoot at something I can't completely see and identify, so thats what the light is for.  I can make out the sights just fine with the light.

However, if night sights are a must, MEPRO's are the way to go by far.