Hello, that's a bug often happens. Not very annoying (except when I start counting my ammo when I have only a few bullets left, and I see that I just lost 2-3 bullets just when reloading) but it's a bit weird :
When I reload, the number of bullets after reload isn't always the same as before the reload, for example :
0-120
(reload)
30-87
Where are the 3 missing bullets ?
I think that's due both to lag and the SMG's high rate of fire, as I never noticed it for the rifle or the shotgun.