Just picked up my first HK a few weeks ago, a USP Compact. Been shooting SIGs for quite a while & am pretty accurate with them but all three trips to the range I have been shooting my USPc about 3-4" lower than point of aim. I had two friends shoot it tonight as well (they also shoot mainly SIG & Glock and was their first time shooting an HK) and they also were shooting low with it. Is there some mystery to getting this thing to hit on target? Thanks for the input.