As you have figured out the Broad Breasted (Bronze or White) varieties have been developed for fast growth and large sizes. I got my BBB during the Easter weekend and was going to butcher when they were between 16-18 weeks for a nice 18lbs but my hubby and I got a cold and then had weather delays. So my tom was butchered around 20 weeks and finished dressed at 27lbs (hens at 22lbs and 24lbs. But since I eat a lot of turkey I wanted to put them all in the freezer (1 Tom and 2 hens) so having it fresh for Thanksgiving wasn't a big priority.
What you want to try and do is get the BBB or BBW about 16 weeks before Thanksgiving. If you want a 16-20lb (depending on type and amount of feed) get them as chicks between the first week of July/first week of August. Toms will be larger than hens of the same age.
My BBB were too dumb and wouldn't forage so my feed cost was a bit high and the only thing I gained was antibiotic free, guaranteed healthy birds for my dinner table.
My plan is to get Heritage next spring (May/April) as I don't mind a smaller bird and they will forage for a lot of their own food along with their primary feed so I hope to reduce feed costs.
According to the book I have "Storey's Guide to Raising Turkeys" the standard (live weight) for the following breeds are:
Standard Heritage Turkey Breeds:
Beltsville Small White: 21lbs Male / 12lbs Female
Beltsville Small Black: 33lbs Male / 18lbs Female
Bourben Red: 33lbs Male / 18lbs Female
Bronze (not BBB): 36lbs Male / 20lbs Female
Narragansett: 33lbs Male / 18lbs Female
Royal Palm: 22lbs Male / 12lbs Female
Slate: 33lbs Male / 18lbs Female
White Holland: 36lbs Male / 20lbs Female
Non-Standard Heritage Turkey Breeds:
Auburn: 25lbs Male / 16lbs Female
Chocolate: 23lbs Male / 14lbs Female
Jersey Buff: 21lbs Male / 12lbs Female
Midget White: 13lbs Male / 8lbs Female
Regal Red: 23lbs Male / 14lbs Female
Sweetgrass: 17-25lbs Male / 12-16lbs Female
How much meat you get will depend on a few things: when they are weighed (before or after eating), how much fat they have vs how lean, etc). But you can guestimate that you will get approx. 70-75% of live weight when it's dressed out (lose 25-30% waste of feathers, organs, feet, head, etc.). So a 33lb Bourben Red tom could dress out at 24-25lbs give or take.
Hope that helps you plan for next years Heritage Breed Turkey.
Edited by Free Spirit - 11/26/15 at 7:36am