Model 1921AC (1926) While not a new model in the usual sense of incorporating major changes, in 1926 the Cutts Compensator (a muzzle brake) was offered as an option for the M1921; Thompsons with the compensator were cataloged as No. 21AC at the original price of $200.00, with the plain M1921 designated No. 21A at a reduced price of $175.00. The Model 1921 was thereafter referred to as Model 1921A or Model 1921AC, though some collectors still refer to it as the Model 1921.
Model 1921AC (1926) While not a new model in the usual sense of incorporating major changes, in 1926 the Cutts Compensator (a muzzle brake) was offered as an option for the M1921; Thompsons with the compensator were cataloged as No. 21AC at the original price of $200.00 with the plain M1921 designated No. 21A at a reduced price of $175.00. The Model 1921 was thereafter referred to as Model 1921A or Model 1921AC, though some collectors still refer to it as the Model 1921.