Very Rare Colt made Thompson M1921 / M1928 Magazine

This is a very rare genuine Colt "Blank XX" manufactured 20 round magazine for the Thompson M1921 and M1928 machine guns. Several makers, Colt, AO and Sparks- Withington produced similar "blank" magazines without any markings. Identifing who made which one is done using the following checks; the hole spacing, follower design and feed lip design. Colt spaced thier viewing holes 0.35 inches from the back of the body to the middle of the holes, and there should be be a small stress relief hole punched just above the follower tab on the back of follower. Finally the design/angle of the front of the feed lips of Colt Blank magazines is a much sharper radius. Colt produced the first 15,000 M1921's issued with these early magazines. Only 15,000 of this type of magazine were ever made!