I load most of my bullets on a progressive press (the older Dillon RL 1000) and load a thousand or better at a time.
A few years ago I had a lot of Unique (from the 70-80s) and ran out in the process of loading a bunch of 38s. So I finished up the batch with new unique.
I couldn't tell the difference, either i recoil, over a chronograph, or the target.
The only difference I could see was they change the outside of the can.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071