these are the 2 guns im actually looking at buying only im only going to get one. and i have a few questions about each gun. 1. how comfortable are each guns to shoot ive only held the ump with the folding stock. 2. how much do conversions cost on the ps90 to shorten the barrel and how much are the conversions on the hk usc to shorten the barrel and a folding stock. 3.how much price difference is there in ammunition and how many rounds come in a box of 5.7 ammo. 4. what are the rpics of the 2 guns. Any help would be greatly appreciated.