The reason you are getting more recoil from lead than jacketed (same weight) is that it takes more of the powder's chemical energy to squeeze the hard stiff jacket down the forcing cone and bore. The relatively soft and slick pure lead requires less energy.
Therefore, that extra energy available to the lead bullet translates into more velocity, and this extra velocity produces more recoil.
Roughly (very) you get about 100fps more velocity with lead than jacketed.
Keithcarter
NRA Life