Cast boolit bhn question lead hardness rifle HP mold

[JackDavis]

I’ve got a 311359 hp mold I picked up on eBay. Casting for 30 carbine aprox 1800 fps
How soft of lead can I go gas checked conventional lubed? I know too hard it will shatter like a varmint boolit.

[Delkal]

You can probably go softer but I cast all of my 30 cal rifle bullets at BHN 15. I doubt you will get shattering at 1800 and when in doubt add more tin.

For game I usually use Lyman #2 (5:5:90) but for the carbine 2.5:2.5:95 at BHN 12-13? should work well.