It's on hold while my 4 bore is being built. The 4 bore is a once-in-a-lifetime opportunity and is taking precedence. This is still on the books. Have a brass manufacturer lined up.
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Please contact Mr. Hollowpoint aka Bob Vogel : https://www.mrhollowpoint.com/index.html
He's an expert on huge hollowpoint bullets for airguns, so he knows a thing or two about the subject.
The slower your bullet goes the less drag becomes a problem and i think you are overthinking it with the plastic tip thing.
This reminds me that I have various .58 caliber minie molds with an adjustable length plain base plug, to try and see how much powder it takes to make them expand into the rifling.
Big bore, your project sounds like a fun one.
Maybe check LeHigh Defence: https://www.lehighdefense.com/bullet...xpansionr.html
They also makes a brand new airgun bullet: https://www.lehighdefense.com/500-ca...n-bullets.html
So copy and paste?