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Work order — Thompson Submachine Gun

Taking the firearm apart for a job such as refinishing, and putting it back together to specification. Generated from the Pew-Takedown entry last updated 2026-10-29. Confidence: medium.

Shop difficulty: Tier 2 of 3

Only 38 numbered components, but the frame (trigger) group is held by a pivot plate under several springs. The FM says to press trigger and sear down while the plate is withdrawn, and the bolt's hammer, firing pin and spring spring out. The frame has to be withdrawn with a downward pull or it damages the trigger and trip. These are several traps but no timing. 38 parts (Models 1921/1928 component list 1–38 (magazines and sight sub-parts not included)). Pew-Takedown's rating, not the manufacturer's.

Bench time: strip ~50 min, rebuild ~80 min (estimate). Actual: strip ______ rebuild ______

Special tools:

• hard-wood block, leather vise jaws and strap wrench — Barrel removal per TM 9-1215 (not normally needed)

Watch for:

• The sear and trigger pivots are held by a pivot plate under spring pressure. It has to be popped and withdrawn straight while the trigger and sear are pressed down. (both; War Department)
• Pushing out the bolt's hammer pin lets the hammer, firing pin and spring spring out and get lost. (disassembly; War Department)
• The lower (frame) group must be pulled down as well as back when it comes off, or the frame latch hits and damages the trigger and trip. (disassembly; War Department)
• The long recoil spring can fly loose and kink between actuator and buffer pilot, then bind. (both; War Department)

1. Clear and make safe

1. Point the muzzle in a safe direction and keep your finger off the trigger.
2. Place the selector and safety on safe.
3. Release and remove the magazine or drum.
   Tip: A drum slides out sideways on the M1928; a box magazine releases with a catch.
4. Pull the actuator fully rearward and lock the bolt open.
5. Inspect the chamber and magazine well with a light and physically confirm the chamber is empty.
   Warning: Look and feel.
6. Remove all live ammunition from the work area.

2. Disassemble

Manufacturer's video: Auto-Ordnance Boot Camp: Tommy Gun Disassembly (Kahr Firearms Group)
https://www.youtube.com/watch?v=6tCsPMop_Lg

Field Strip

1. Complete the Clear and Make Safe procedure with the bolt forward and the safety on.
2. Press the frame latch and slide the lower receiver group rearward and off the upper receiver.
   Warning: Hold the trigger pulled and pull the frame down as well as to the rear as you withdraw it. If you do not pull down, the frame latch strikes the rear of the trigger and trip and damages them (FM 23-40 para 6c).
3. Withdraw the actuator, bolt, and recoil spring assembly rearward out of the upper receiver.
   Warning: The recoil spring is under compression.
4. On an M1928 pattern, slide the actuator with the lock forward and lift the lock (the Blish H-piece) out of the actuator.
   Warning: M1 and M1A1 bolts have no H-piece. Do not go looking for one.
5. Clean the bore, chamber, bolt face, and receiver interior.

Remove the breech oiler

1. Field strip the gun so that the frame, recoil spring, bolt, lock and actuator are out of the receiver.
2. Hold the receiver upside down in your left hand, muzzle to the front.
3. Hook the end of your right forefinger under the front end of the right side of the breech oiler and pull up and to the left until the right side of the oiler is out of its groove in the receiver.
4. Hold the oiler in this position with your right thumb.
5. Without moving the thumb, hook your right forefinger under the front end of the left side of the oiler and pull the oiler out of the groove in the left side of the receiver.
6. With your right forefinger, pull the entire front end of the oiler up and to the rear.
7. Lift the oiler out of the receiver, front end first.

Disassemble the 20-round box and 50-round drum magazines

1. Box magazine: slide out the floor plate while holding your fingers over the bottom of the magazine tube.
   Warning: Hold fingers over bottom of magazine tube to keep magazine spring from flying out.
2. Box magazine: remove the magazine spring and the follower.
3. Drum magazine: remove the winding key.
4. Drum magazine: lift off the cover.
5. Drum magazine: lift up on the end of the rotor retainer and slide it out of its engagement in the hub.
6. Drum magazine: remove the rotor assembly from the body.
   Warning: Further disassembly of magazine is not necessary and is prohibited (FM para 7a). TM 9-1215 para 12 adds that the rotor and spring case are riveted together.

Disassemble the bolt group

1. Field strip the gun and take the bolt out of the receiver.
2. Push the hammer pin out of the bolt from the left side.
   Warning: The hammer, firing pin and firing pin spring will tend to spring out under the impulse of the firing pin spring. Keep them from springing away and becoming lost. The firing pin spring must not be stretched.
3. Only if the extractor must come out, insert a corner of the actuator flange under the head of the extractor on the face of the bolt and pull the extractor out and up to withdraw it from its groove.
   Warning: Do not remove the extractor for ordinary cleaning — it is apt to break or take a set. Do not lift it higher than necessary for its lug to clear the anchorage hole.

Remove the rear sight leaf, ejector and fore grip

1. Field strip the gun so that the bolt is out of the receiver.
2. Drive out the sight base pin and remove the rear sight leaf.
   Warning: Take care that the rear sight leaf plunger and spring do not fly out.
3. Lift the leaf just enough to disengage the detent, and unscrew the ejector from the receiver.
   Warning: Do not try to unscrew the ejector with the bolt assembled and in the forward position. To do so may damage the ejector and bolt.
4. Unscrew the fore grip screw and remove the fore grip.

Disassemble the butt stock

1. Remove the butt stock from the gun.
2. Remove the screws and lift out the butt stock slide assembly.
3. Drive out the butt stock catch pin and remove the catch and its spring.
4. Only to remove the catch button, file its pin to round and drive it out.
5. Remove the butt stock plate.
6. If necessary, remove the trap spring and drive out the trap pin.
   Tip: The bracket is riveted to the butt plate; leave it.
7. Remove the sling swivel screws and lift out the swivel plate.
8. If necessary, spring the swivel from the plate.

Remove the barrel, compensator and front sight

1. Disassemble the gun so that only the receiver and barrel remain.
2. Wedge a block of hard wood in the receiver to prevent springing of the sides.
3. Clamp the receiver in a vise with leather jaws.
4. Unscrew the barrel from the receiver with a strap wrench.
   Tip: A pipe wrench may be used only if the barrel is to be scrapped.
5. To move the front sight and compensator to a new barrel, drive out the front sight pin.
   Tip: TM para 10c(1): do not remove compensator or sight unless necessary.
6. Drive the front sight rearward off the barrel.
7. Unscrew the compensator with a strap wrench.

3. Refinish

The components the procedures above separate. Coating, masking and cure are outside this database; follow your coating system's instructions. A part the manufacturer marks "factory fit" should not be swapped or reworked.

The manufacturer's full parts list (38 parts) is on the reference page.

4. Reassemble

Remove the barrel, compensator and front sight

1. Reverse the steps of "Remove the barrel, compensator and front sight".

Disassemble the butt stock

1. Reverse the steps of "Disassemble the butt stock".

Remove the rear sight leaf, ejector and fore grip

1. Reverse the steps of "Remove the rear sight leaf, ejector and fore grip".

Disassemble the bolt group

1. Reverse the steps of "Disassemble the bolt group".

Disassemble the 20-round box and 50-round drum magazines

1. Reverse the steps of "Disassemble the 20-round box and 50-round drum magazines".

Remove the breech oiler

1. Reverse the steps of "Remove the breech oiler".

Reassemble the box and drum magazines

1. Drum magazine: place the rotor assembly in the body.
2. Drum magazine: slide the rotor retainer back into its engagement in the hub.
3. Drum magazine: replace the cover.
4. Drum magazine: replace the winding key.
5. Box magazine: insert the follower and magazine spring into the tube.
6. Box magazine: compress the spring with your fingers and slide the floor plate back on.
   Warning: Keep the spring covered with your fingers so it cannot fly out.

Reassemble the bolt group

1. If the extractor was removed, slide it into place, lifting its head only enough to clear the stud.
   Warning: Avoid excessive pressure on the extractor.
2. Insert the firing pin and firing pin spring in the bolt.
   Warning: Do not stretch the firing pin spring.
3. Place the hammer in position with its rounded edge upward.
4. Push the hammer pin into place.

Reinstall the fore grip, ejector, rear sight leaf and breech oiler

1. Install the fore grip and screw in the fore grip screw.
2. With the bolt out of the receiver, screw the ejector all the way home.
3. Place the rear sight leaf plunger and spring, position the rear sight leaf and drive in the sight base pin.
   Warning: Keep the plunger and spring from flying out.
4. Reinstall the breech oiler, rear end first, by reversing the removal steps so that both sides seat in their grooves in the receiver.
5. Replace the actuator, lock, bolt, recoil spring and frame as in the entry's reassembly procedure.

Reassembly

1. On an M1928 pattern, place the lock in the actuator guideways with the word "UP" readable from the rear and the arrow pointing toward the muzzle.
2. Insert the bolt, actuator, and recoil spring assembly into the upper receiver and seat them.
3. Slide the lower receiver group onto the upper until the frame latch engages.
   Warning: Confirm the latch is engaged before handling the weapon further.
4. Cycle the action several times and perform the function check.

5. Torque

No manufacturer torque values are recorded for this firearm.

Notes: The official military manuals give no torque value. They say: "If the rear grip is loose, inspect screw threads in frame and on screw for wear, and the screw for straightness." (TM 9-1215 Ordnance Maintenance: Thompson Submachine Gun cal .45, M1928A1 (1942), PDF p. 6 (frame))

Fit or check on rebuild

• Frame latch engaged — The frame must be locked to the receiver.
• Function check (safety, trigger reset, feeding, extraction) — Standard after any detail strip. No single source.

6. Function check

• Verify the firearm is unloaded with no magazine inserted before each step.
• Cycle the action by hand and confirm the bolt returns fully into battery.
• With the safety on, press the trigger. The hammer or striker must not release.
• Move the safety to fire, cycle the action, and press the trigger. It should release.
• Hold the trigger back, cycle the action, and release slowly to feel the disconnector reset.
• Confirm the magazine seats and locks positively and releases cleanly.
• Confirm the upper and lower receiver groups are latched together securely.
• Confirm the actuator moves freely through its full travel.

If any check fails, the firearm is not safe to fire. Stop and see a licensed gunsmith.

Sources

1. FM 23-40: Thompson Submachine Gun, Caliber .45, M1928A1 — U.S. War Department primary
2. TM 9-1215: Thompson Submachine Guns, Caliber .45, M1 and M1A1 — U.S. Department of the Army primary
3. TM 9-1215 Ordnance Maintenance: Thompson Submachine Gun cal .45, M1928A1 (1942) — War Department (US Army), 1942 primary
   https://archive.org/details/TM9-1215
4. Handbook of the Thompson Submachine Gun, Model of 1928, Model of 1921; Thompson Semi-Automatic Carbine, Model of 1927 (4th Edition, January 1929) — Auto-Ordnance Corporation, New York primary
   https://archive.org/download/gunmanual_Thompson_Tommy_Full_Auto_1927/Thompson%20Tommy%20Full%20Auto%201927.pdf
5. Thompson 1927A-1 — Overview and Specs (Auto-Ordnance) — Auto-Ordnance (Kahr Firearms Group) primary
   https://www.auto-ordnance.com/thompson-1927a-1/
6. Auto-Ordnance (Kahr Firearms Group) — — Auto-Ordnance (Kahr Firearms Group) primary
   https://www.auto-ordnance.com/thompson-m1/
7. FM 23-40 Basic Field Manual: Thompson Submachine Gun, Caliber .45, M1928A1 (with Changes 1–4) — War Department primary
   https://archive.org/download/FM_23_40_B_F_M_T_S_G_C_45_M1928A1_1931/FM%2023-40%20Basic%20Field%20Manual.%20Thompson%20Submachine%20Gun%2C%20Caliber%20.45%2C%20M1928A1%20%281931%29.pdf
8. TM 9-1215 Ordnance Maintenance: Thompson Submachine Gun, Cal. .45, M1928A1 — War Department primary
   https://archive.org/download/TM9-1215/TM9-1215.pdf

Educational guide only. Some information comes from non-authoritative sources. Always consult your manufacturer's manual and a licensed gunsmith. Verify your firearm is unloaded before every procedure. Full disclaimer: https://github.com/Fundamental-build-LLC/Pew-Takedown

Legal notice: this material is third-party information compiled from sources of varying reliability and is provided for general informational and educational purposes only. It is not gunsmithing, technical, safety or legal advice, it is not verified or endorsed by any manufacturer, and it must not be taken as fact. Any work on a firearm beyond the routine field stripping described in its own owner's manual should be performed only by a licensed and insured gunsmith. You use this material entirely at your own risk. Fundamental Build LLC and the project's contributors make no warranty of any kind and accept no liability for death, injury, damage or loss arising from its use. Full terms: LEGAL.md.