Filling that cavity with "P-Tex" ski base repair plastic, or just common epoxy kicks the chit out of expansion ratios too.

Hell, try cutting "Dum Dum" grooves into it,....you can than hear it whistle on it's way down range.

You'll not be HITTING anything, but if you want to freak out your fellow shooters,...drill a hole through the front of a bullet,.....they'll land in the general vicinity of where your barrel's pointed,.....and make a blood curdling shriek, so doing.

Screamers,....hard on morale, back in the day, funnier than hell now.

GTC

Member, Clan of the Border Rats
-- “Sometimes I wonder whether the world is being run by smart people who are putting us on or by imbeciles who really mean it.”- Mark Twain