I have some old REM-UMC 30USA brass that varies by as much as 30gr.  I bought it once fired.  Some of the heavier brass had obviously been loaded to higher pressure.  Could be someone loaded the heavier brass with the same load that that they were using in the lighter brass and got the higher pressure.  So, yes, those weight differences can cause a difference in pressure, velocity and results.  One could work up a near max load in the light brass, put that same load in the heavier brass and experience sticky extraction or observe other pressure signs.  It became apparent there were two lots in the 200 cases I'd bought and the weight variation wasn't so big once sorted into lots by weight.