Math is apparently NOT ubisoft's forte - by my math it's 4% not 5...
ps - and sometimes less than that as they round "down" - odd thing is that at times ya do get 5%. THE FIRST TIME - but then it immediately begins to diminish due to the rounding - For example : I had 800 damage and they gave me 5% so I had 840 damage - when I upgraded again immediately instead 882 I got 880 damage and by the time I got that junk SA-50 up 1000 damage and began to upgrade it again they gave me 4% and I had 1040 damage - their math is so wonky it's not even consistent....