I used maths for this challenge, at the end of last year. I measured up 10 clefts from another supplier, and they averaged out at 0.41 grams per cubic centimetre. Try measuring, and weighing, if you need my spreadsheet I can send it over, enter the data and Excel will make the calculations for you.
Now that spreadsheet sounds just the thing Ive been looking for. Was looking to create something similar but need some raw data from other clefts. I won't buy any now as Ive got my own so I can't cross reverence any. Any that Ive bought in the past are now bats or handled part shaped things - so need some data from other people in regards to cleft weights. That'll help me get a better measure of the weight and readiness for the timber to become a bat. If you could email it me that'd be great !