Bullet size
Bullets for any caliber run the gamut in weight from very light bullets to very heavy. For instance, typical military rounds for 7.62 run from 147 to 203 grains. Obviously, the lighter bullets are much shorter. The loading specs call for a certain overall length regardless of bullet weight for purposes of feeding. Consequently, you can't tell heavy from light bullets by simply looking. The heavy bullets are simply seated deeper into the case as others have mentioned. Heavy ball versus light ball ammo varies much more in bullet size than a hollow point variation will cause. So there is no problem that needs to be solved by a variation in lead mix. Of more importance, size and shape of the bullet will affect the stabilization of the bullet and thus accuracy. Only shooting the individual gun will determine which is best, although there are trends that carry over from one gun to the next because of twist rates and similar conditions in guns of the same model.