That flat part of the bullet is called thye Meplat. They make meplat trimmers for different case trimmers. However I don't think you will like the results of trimming or changing that meplat. The larger and the flatter the better for both accuracy and uniform expansion.

Add a little WW if you want a slightly larger bulet. The harder the alloy the larger the bullet will drop from the mold. Tom.

maybe an small step drill bit (drill to the first step and stopping half way) and an drill press could do the trick but holding it in place would be the next trick. only way I have heard of hollow pointing cast bullets other then an mold for one is to have it mounted on the brass.

but with how it mushroomed, I would not try it myself..

now something taking that design and hollow basing it, that would be something else

Let the meplat work, IMHO, there is no reason to hollow point a perfect big meplat other than to change the cg of the bullet. that is only needed to correct flight characteristics.

Because you are shooting them bare, less a sabot you need soft lead to obterate to fill/seal the bore.

Let the projectile do its job.

Have fun.

It should be self evident that a boolit of over an ounce in weight will lower the level of melt in any size pot very quickly, I have a mold that drops 4, 500 gr .512 WFNs every time I open it. yes almost 5 ounces a throw. :-)