There are several parts in the movie sniper where first you see the gun camoflauged and then you don't.

First slip-up: When Dsyliva searches for Zane and Beckett, You see several parts where his SVD is covered in burlap and several you don't

Second slip-up: When Zane is at the red tractor you see is gun is hardly covered but in the next shot his SR9 is covered.