View Full Version : 1928 Thompson

June 1, 2000, 10:05 AM
Acquired a 1928 Thompson, The problem is when
the selector is in semi mode I get get bursts of three to five shots. Any idea what may be causing this.
e-mail me at [email protected] if you can help.


James K
June 1, 2000, 02:52 PM
The Thompsons (like most SMGs) fire either semi or full from an open bolt, which is held back by the sear. If the sear does not hold, the gun will go full auto regardless of the switch position. It is also possible that the disconnector is broken or not working properly. (In the Thompson, the disconnector is in the top front of the trigger group.)

Assuming there is no dirt or anything interfering with the proper operation, I would try replacing the sear. That is more likely to be the cause than the disconnector, but replacing both would be a good idea and should solve the problem.

Gun Parts Corp. has parts for the 28.


James K
June 1, 2000, 10:32 PM
Forgot to mention another quirk of SMGs. If the loads are too light (usually if handloads are used) the bolt will not blow back far enough to be engaged by the sear and the resulting firing cannot be stopped by releasing the trigger. This will occur regardless of the position of the selector.

As info, much of the 9mm ammo the U.S. sent to England in WWII, was so weak the STEN could not be "shut off" until the magazine was empty. The British marked the stuff "NOT FOR STEN" which some American perversely believe means it is too powerful for SMGs, when the opposite is true.



Rocky Road
June 12, 2000, 11:48 PM

If you don''t already have some literature on yout TSMG, you might want to get some. You can only shoot so many rounds, and you gotta stay home from the range some weekends.

The 1942 War Department manual, TM 9-1215, has full detail stripping information on the 1928A1 Thompson. On page 25 there is a good illustration of the relationship of the frame and the parts contained therein. Part A is the rocker. Note that the semi-circular cut out is toward the rear of the frame. On the opposite page, page 24, item b (3), the assembly instructions state,
"If rocker is assembled backward, the gun will fire full automatic but not semiautomatic."

I have fired two TSMGs, some 25 years apart, which wouldn't reliably function in the semi mode. One was a Savage-made 1928A1 and the other was an M1-A1. Each time, I found the rocker was mis-assembled. Now that I write this, I realize I've never purposely set my own TSMG up that way. Maybe on next trip to the range . . .

Hope you enjoy yours as much as I have mine. Best regards.

---The Second Amendment ensures the rest of the Bill of Rights---

James K
June 13, 2000, 10:41 PM
My apologies for the nomenclature error, but it has been a long time since I looked at a manual. What I was calling the disconnector is, as Rocky Road says, correctly called the rocker. It is a good spare part to have, as it can get beat up, especially from improper disassembly/assembly.