Quickad,
HK USP vs Sig P220 for accuracy? Personally, I can't imagine another out of the box .45 being any more accurate than the Sig P220.
I've fired the USP in 9, 40 and .45 and while these were all excellently accurate, I don't believe they are superior to any Sig.
There have been some tests of Sig's P220 from a ransom rest where the P220 fired a five round 7/8" group at 25yds. (I can site the article if you want me to research it).
The above test appeared in a popular gun rag as well as Sig's own excellent, albeit biased publication. I have no doubt that at a given time, temp., elevation, comparable load that the HK could duplicate this level of accuracy; however, I doubt the USP could surpass this.
Since both the SIG and USP are capable of putting a mag into a 3x5" note card offhand at 25 yds. they are both perfectly acceptable for defensive purposes. Any measure of accuracy beyond this is purely academic for defensive weapons such as these.