New Thompson 1927 A1

rhuff · 07-31-2012, 04:15 PM

I am pretty sure that your semi-auto Thompson is a pure blow-back action, as was the original Thompson, and not a locked breach action. The Thompson M1, and M1A had a fixed firing pin in the breachface, and when the bolt reached battery, or slightly before battery, the primer was ignited, and the whole process started over. The selector switch changed the sear engagement between the semi and full auto mode on the 1921, 1925, and 1928 models. I don't own an M1, or M1A, so am not really sure exactly how the selector switch functions, but likely very similar.

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07-31-2012, 04:15 PM	#11
rhuff Patron LugerForum Patron Join Date: Mar 2011 Location: Az. Posts: 2,316 Thanks: 2,762 Thanked 1,000 Times in 735 Posts	I am pretty sure that your semi-auto Thompson is a pure blow-back action, as was the original Thompson, and not a locked breach action. The Thompson M1, and M1A had a fixed firing pin in the breachface, and when the bolt reached battery, or slightly before battery, the primer was ignited, and the whole process started over. The selector switch changed the sear engagement between the semi and full auto mode on the 1921, 1925, and 1928 models. I don't own an M1, or M1A, so am not really sure exactly how the selector switch functions, but likely very similar.