https://www.doublegunshop.com/forums...&Number=665300
Have never seen an 'M'. I don't believe it is a Belgian tube maker's mark; usually further forward and different font.
The gun dates to the period when Parker Bros. was fabricating Twist and Laminated Steel tubes in house.
A Lifter with Twist barrels; ‘PB’ in a shield, ‘T’ for Twist, J.L. and an unknown mark
