Those weights are actually for the whole projectile weight, not the core weight. The core weights are equal. About 3/4 of a pound according to TM-1985-3.The 50 mm Pzgr.40 weighed .92 Kg, the 40/1 1.07 Kg (cores in their 50 mm rounds)
The propellant weights must be different, given the difference in KE between the projectiles. But that is another subject. The KE can then be misleading....
KE = 1/2MV^2
KE (40)= 640.5
In terms of penetration, they both actually have the 'same' actual penetrator. That is, the 'bolt', and while there will be a difference in flight characteristics, the end effects will be dependant on velocity at that range. Penetration for the '40' probably would be greater at shorter range, the '40/1' would probably overtake it at longer ranges.
Given the shorter ranges this ammunition should have been used at, they were both probably extremely accurate to the point of being immune to range estimation errors. Even accurate enough to be more selective regarding the actual area of the target to strike. If you look at the mechanical drawings I posted above, the 40/1 has a streamlined body while the 40 has a 'notched' body.