undersized cast...

[ratherbefishin]

what do you do if you got a batch of cast that was slightly undersized for your bore[rifle]-apart from melting them down?I am referring to regular powder-not Black powder

[jhalcott]

  I try to cast only a dozen or so bullets to check for that . I can vary the diameter a bit by using a bit more tin in the alloy. Or casting at a higher temperature. You COULD beagle the mold. This means lapping it to a larger diameter. A couple strips of aluminum tape between the halves will open the mold a few thousandths.
  As far as the ones in hand, a coating af Lee Liquid ALOX MIGHT help. If they are quite soft ,you can try swaging them in your sizing die. This may NOT help accuracy though.

[Lloyd Smale]

theyd go back in the pot if they were mine.

[Graybeard]

There really isn't anything much to do but melt them or give/trade/sell them to someone who can use them at that size or for alloy to make more proper size bullets. You can't make them larger or your barrel smaller.