Dad has a 504 with a '40' on the barrel an he was wondering the significance of this number. He thought that he had read somewhere that these were possibly the same barrels that Remington put on there 40x rifles. Just curious. Thanks.

I seriously doubt the 40 has any special significance. Remington has always had numbers and characters stamped on their barrels that mean nothing to the consumer but are internal codes for heat treating, inspections, etc. Examples were inspectors anchor stamps that had nothing to do with the navy and a heart stamp that did NOT indicate Hart made barrels.

I assumed that to be the case. Thanks for the input.