That's my problem. My chambers are too small with quench at a .030-.035". Instead of using different heads i was considering milling a small pocket, maybe 6cc or so.

The deck is .005 in the hole with a 58cc closed chamber iron head. too much compression with quench.

Not sure what you mean by "Your bob weight will change by 50% of the weight change."

I guess I need to do some calculations to see just what size pocket I need to mill to figure how many grams weight change will be.