I just call it lag...it's almost the same with every other shooters out there...
Your ping will most likely to determine your faith...
often times I fire the MP40 the same time as the enemy firing a PPsh at me, but guess what, he didn't even get hit at all...even tho PPSh is much more better in clearing rooms, but at least my mp40 will get AT LEAST one bullet in him before I die, cause from my screen seems like I fired first (and I shot like 4 bullets to him at a CQC 0-3m)..but to him he fired first...So I just blame the ping...