I have some doubt about the "net weight" theory, since shippers usually deduct "tare" from containers they provide to clients. (I'm willing to be corrected on that; I am no expert on shipping, and yes, I am not - unlike the Pope, allegedly - infallible.)
But if we go with your proposition on shipping weight of the rifles, 750lbs for 100 units, then the rifles would be 7.5lbs each, i.e. 40" rifle, not the 36" model Oswald ordered. No? Yes?
Yes, The 40 inch long, 7.5 pound, model 91/38 Mannlicher Carcano short rifle is the rifle that was sent to PO box 2915 in Dallas.... But when it was shipped to Dallas it had a scope attached which increased the weight to 8 pounds. I believe that it is the same rifle that was found on the sixth floor where it had been carefully hidden beneath a pallet that had boxes of books stacked on it ( It had NOT been hastily cast aside) ...And it had NOT been fired that day....So it was NOT the murder weapon.
The Carcano was found well hidden beneath a heavy pallet of boxes of books. Boone and Weitzman had to use powerful flashlights to enable them to see beneath the pallet where the rifle was lying on it's right side ( Sling and scope up) Detective Robert Studebaker measured the distance from the interior side of the north wall of the building and recorded that the rifle was 25 feet 4 inches south of that north wall and 5 feet east of the west wall. (See Studebaker's map) The in situ photos that purportedly show the rifle as it was found are fakes. The rifle in the in situ photo is only 13 feet from that north wall.
The DPD was forced to move the rifle over two feet north when someone realized that there wasn't a human being on earth who could reach across the distance from the aisle at the top of the stairs and place the rifle down on the floor beneath a stack of books that was four feet high.