I have a heart girth tape right in front of me as I was measuring some of my own. This is what they have for 51 inches:
Thin 433 pounds
Moderate 414
Fleshy 391
Very Fleshy 371
Take this with a grain of salt. I knew there would be inaccuracies with the weight tape but I wanted to know how different the weights would be compared to scale weighing. So I measured 3 of my heifers that we did 205 day weights on 2 weeks ago. Should have done it on the day of but I didn't have a tape. Anyway, this was the result:
Heifer #1 - Actual= 698 Tape = 656
Heifer #2- Actual= 703 Tape = 715
Heifer #3 - Actual= 626 Tape= 686
I also had a heifer that was 165 days old and weighed 531, the tape weighed her in at 534 (two weeks later).