My newest investment in 5.56. I dig this thing. I'm considering an interchangeable barrel set-up in 6.8 Rem. ammo costs a fortune though.
I have run two HK's, the UMP and the MP5, there is no denying that the MP5 is slick, I liked the UMP also in spite of the enormous, heavy bolt throwing 45 ACP.
I have a couple Colt AR's too. I think I'm set for 5.56......but the HK is a good setup.