We have yet to find a velocity too high. We do not have bullets that break to pieces. I'm sure there is a limit, but impacts above 4000 fps still yield nearly the same weight retention as 1800 fps impacts. We have been able to make 100g 30 cal Shock Hammer squish too much, at 4200 fps, for it to penetrate to our satisfaction.
This week we had a film crew here to conduct a gel test. We tested our 199g 30cal Hammer Hunter against another bullet. Prior to the video getting done, I will only say the Hammer worked perfectly with a velocity range of 1400 fps impacts. Retained weight varies by 5g.
Not all coppers are equal. Not even close.