I have been looking at H&K's and I don't see any .45's on gunbroker. Why is it that the .40 and the 9mm are more popular than the .45, are there any problems present in the .45 that could be responsible or is it just that the .40 and the 9mm are more popular?

Could anybody explain to me or give a link to the descriptions of the different variants?

It would seem to me that perhaps your logic is a bit off. IMO there's no 45s listed is because maybe they're sold out of them? I carry a USP Compact S/S in 45acp & have used it for IDPA as well. My guess is that the USP 45 is for the more "experienced" gun owner whereas the 9mm & 40S&W grab the attention of the lessor experienced shooter? After, the legend is that a 45 will blow a huge hole thru someone so recoil must be equal, right? Or so the novice perhaps thinks. Or at least this has been my experience at working gun shows for many years. But I can assure you, there's NOTHING wrong with the USP 45. If I had the $$, I'd get another, the Tactical or Match model. My .o2

Agree with Bob Cole, most of the used guns I see are the ones people are selling to get something good.

It seems like most civvies gravitate to the .45.

Quoted:It seems like most civvies gravitate to the .45.

Well, I'm a civvy & I like the 45acp. >gg< I was a Marine but strangely enough never once fired a 45 in the entire six years I was in. Of course I own nearly all calibers except the 40/10 & mouse guns.