I did some looking on the internet. The University of Wyoming did a study and they found that an elk give 50% of the field dressed weight back in boneless meat. Field dressed weight is gutted and legs removed but with head and skin on. They found head and skin weighs 73lbs. So 73lbs + 168lbs (boneless meat from a 2.5 year old elk) = 241lbs so that leaves 94lbs for the skeleton because they found a 2.5 year old bull is 337lbs average.
So my elk weighed 323lbs on the with no head or skin. So according to this study there should have been 239lbs of boneless meat. I received half of that.
http://www.wyomingextension.org/agpubs/pubs/B594R.pdf