The question is meaningless unless "Which part of Texas" is specified.
The biggest ones I've seen come from two areas a few hundred miles apart; the S Tx Brush Country and the Canadian River Bottoms.
Here in N Central Tx, the largest I've weighed was 137 lbs. field dressed. I killed another that was at least 20 lbs. heavier.
Given that 90% of the bucks killed in this County - prior to the 13 inch rule - were 2 1/2 Y O or younger, it's hard to determine from P&W data how large they are capable of becoming.
But I'll answer the question for THIS part of Tx by guessing that the AVERAGE field dressed weight of a mature buck will be around 110 lbs.
How about YOUR part of the country?
