Just a thought...I'm sure someone could confirm or deny my idea, but...isn't something that is round more flexible than something that is square. What I'm thinking is if you are going to bed something in the stock, wouldn't aluminium square stock or even small angle be stiffer and lighter than all-thread for the same size. Or maybe even a piece of aluminium square tube in the channel.
I don't know, just a thought. Maybe not a good one.
Genises 27-3: Now therefore take, I pray thee, thy weapons, thy quiver and thy bow, and go out to the field, and take me some venison...