Generally A BB bronze is butchered at around 20 weeks, at this time Males could range in the 24 to 27 pound range females around 18 to 20 or a little less.
You can add or subtract time to get a smaller or larger dressed bird.
As far as feed conversion I recall seeing some info here. But not sure where it is. But normaly on this forum, butcher at 20 weeks as after this time feed cost will be more then what you may get in return.
We raised Great whites and BB bronze along with blue slate and red bourbon. In hind sight I am not really sure why we did the larger turkeys since we have never bought a turkey over 20 pounds.
Our 4 BB White turkeys are 15 weeks and are looking about ready to butcher. I'm looking for about a 15 lb bird dressed. We don't care to raise them up to 20 lb. They eat and eat and eat. Didn't calculate the cost because we have other varieties of turkey, ducks, quail, and chickens that share the starter and such.