Pew-Takedown
Guide only. 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. Read the full disclaimer.

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Thompson Submachine Gun

field strip ~4 min · reassembly ~6 min · detail strip ~35 min

Before you begin Verify this firearm is unloaded. Remove the magazine or empty the cylinder or tube, lock the action open, and check the chamber both by sight and by touch. Keep the muzzle in a safe direction and remove all live ammunition from your work area.
What Auto-Ordnance says about disassembly The 1929 Auto-Ordnance handbook gives owners full dismounting directions down to the firing mechanism, firing pin and extractor, with only cautions (e.g. remove the magazine catch or breech oiler only if necessary). (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, p. 41 archive.org [4])

Specifications

Manufacturer
Auto-Ordnance
Origin
United States
Category
Submachine Gun
Action
Blowback
Calibers
.45 ACP
Capacity
20 or 30 rounds in a box magazine, 50 in a drum
Production
1921–1945 (surplus)
Also known as
M1928A1, M1A1 Thompson, Tommy Gun

Model-specific safety

Under spring tension

Easily lost parts

Blish lock H-piece (M1928 pattern) · Recoil spring and buffer · Actuator · Trigger group pins

Tools

No tools required for the field strip.

Shop difficulty

Shop tier 2 Tier 2 — moderate among rifles and carbines, for the full job: strip to the parts that get coated and put it back together working. 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 The FM says to press trigger and sear down while the plate is withdrawn, and the bolt's hammer, firing pin and spring spring out. The frame has to be withdrawn with a downward pull or it damages the trigger and trip.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.

Parts: 38 numbered parts (Models 1921/1928 component list 1–38 (magazines and sight sub-parts not included)), from 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, p. 7 archive.org [4].

Bench time: about 50 min to strip, 80 min to rebuild (estimate). Frame group (pivot plate, sear, trigger, rocker, safety), bolt group (hammer pin, firing pin), actuator, Blish lock, recoil spring/buffer, butt stock, sights.

Small parts: 3 pins, 7 springs, 0 detents or plungers (counted from the manufacturer's parts list (one per key number unless a quantity is given))

What comes off for coating

Special tools

Known pain points

Fit or check on rebuild

This is Pew-Takedown's rating, not the manufacturer's. How tiers are rated. Forum reports are owners' experience, not specifications.

Manufacturer videos

Official videos from Auto-Ordnance's own channels, linked rather than copied. Where a video and the steps on this page differ, follow the manufacturer's manual and video.

Procedures

Clear and Make Safe

Clear & Make Safe

Box magazines and drums unload differently. Check the chamber independently of either.

  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.
    TipA drum slides out sideways on the M1928; a box magazine releases with a catch.
    Removed at this step: Magazine or drum
  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.
    WarningLook and feel.
  6. Remove all live ammunition from the work area.

Field Strip

Field Strip

Manufacturer’s video: Auto-Ordnance Boot Camp: Tommy Gun Disassembly Kahr Firearms Group

  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.
    WarningHold 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).
    Removed at this step: Lower receiver group
  3. Withdraw the actuator, bolt, and recoil spring assembly rearward out of the upper receiver.
    WarningThe recoil spring is under compression.
    Removed at this step: Actuator Bolt Recoil spring assembly
  4. On an M1928 pattern, slide the actuator with the lock forward and lift the lock (the Blish H-piece) out of the actuator.
    WarningM1 and M1A1 bolts have no H-piece. Do not go looking for one.
    Removed at this step: Blish lock H-piece
  5. Clean the bore, chamber, bolt face, and receiver interior.
  6. Stop here. The fire control group is intricate and parts are scarce.
    WarningIf the weapon is malfunctioning, take it to a gunsmith familiar with the design.

Remove the breech oiler

Detail Strip

FM 23-40 para 6f, a using-arm (operator) task done after the field strip. The FM says it is not needed for ordinary cleaning.

Applies to: M1928A1

Follows FM 23-40 Basic Field Manual: Thompson Submachine Gun, Caliber .45, M1928A1 (with Changes 1–4) — War Department, para 6f (p. 7) archive.org [7]

  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.
    Removed at this step: Breech oiler

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

Detail Strip

FM 23-40 para 7a–b, operator level. The drum is taken apart only as far as removing the rotor assembly.

Applies to: M1928A1

Follows FM 23-40 Basic Field Manual: Thompson Submachine Gun, Caliber .45, M1928A1 (with Changes 1–4) — War Department, para 7a–b (p. 7) archive.org [7]

  1. Box magazine: slide out the floor plate while holding your fingers over the bottom of the magazine tube.
    WarningHold fingers over bottom of magazine tube to keep magazine spring from flying out.
    Removed at this step: Floor plate
  2. Box magazine: remove the magazine spring and the follower.
    Removed at this step: Magazine spring Follower
  3. Drum magazine: remove the winding key.
    Removed at this step: Winding key assembly
  4. Drum magazine: lift off the cover.
    Removed at this step: Cover assembly
  5. Drum magazine: lift up on the end of the rotor retainer and slide it out of its engagement in the hub.
    Removed at this step: Rotor retainer
  6. Drum magazine: remove the rotor assembly from the body.
    WarningFurther 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.
    Removed at this step: Rotor assembly

Disassemble the bolt group

Detail Strip

FM 23-40 para 7e, operator level: hammer pin, hammer, firing pin and spring, and — only to replace it — the extractor.

Applies to: M1928A1

Follows FM 23-40 Basic Field Manual: Thompson Submachine Gun, Caliber .45, M1928A1 (with Changes 1–4) — War Department, para 7e (p. 8) archive.org [7]

  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.
    WarningThe 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.
    Removed at this step: Hammer pin Hammer Firing pin Firing pin spring
  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.
    WarningDo 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.
    Removed at this step: Extractor

Remove the rear sight leaf, ejector and fore grip

Detail Strip tools required

FM 23-40 para 7f. The FM says the receiver and its attached parts need not be taken apart for ordinary training; the barrel is ordnance work (see 'barrel-removal').

Applies to: M1928A1

Follows FM 23-40 Basic Field Manual: Thompson Submachine Gun, Caliber .45, M1928A1 (with Changes 1–4) — War Department, para 7f (p. 8) archive.org [7]

  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.
    WarningTake care that the rear sight leaf plunger and spring do not fly out.
    Removed at this step: Sight base pin Rear sight leaf Rear sight leaf plunger Sight plunger spring
  3. Lift the leaf just enough to disengage the detent, and unscrew the ejector from the receiver.
    WarningDo not try to unscrew the ejector with the bolt assembled and in the forward position. To do so may damage the ejector and bolt.
    Removed at this step: Ejector
  4. Unscrew the fore grip screw and remove the fore grip.
    Removed at this step: Fore grip screw Fore grip

Disassemble the butt stock

Detail Strip tools required gunsmith recommended

TM 9-1215 para 9b, ordnance maintenance (above the using arm). FM 23-40 para 7c lets the user remove the butt stock slide and butt plate by their screws only when a part must be replaced.

Applies to: M1928A1

Follows TM 9-1215 Ordnance Maintenance: Thompson Submachine Gun, Cal. .45, M1928A1 — War Department, para 9b (p. 8) archive.org [8]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  1. Remove the butt stock from the gun.
  2. Remove the screws and lift out the butt stock slide assembly.
    Removed at this step: Butt stock slide assembly Screws
  3. Drive out the butt stock catch pin and remove the catch and its spring.
    Removed at this step: Butt stock catch pin Butt stock catch Butt stock catch spring
  4. Only to remove the catch button, file its pin to round and drive it out.
    Removed at this step: Catch button
  5. Remove the butt stock plate.
    Removed at this step: Butt plate
  6. If necessary, remove the trap spring and drive out the trap pin.
    TipThe bracket is riveted to the butt plate; leave it.
    Removed at this step: Trap spring Trap pin
  7. Remove the sling swivel screws and lift out the swivel plate.
    Removed at this step: Sling swivel screws Swivel plate
  8. If necessary, spring the swivel from the plate.
    Removed at this step: Sling swivel

Remove the barrel, compensator and front sight

Detail Strip tools required gunsmith recommended

TM 9-1215 paras 10c(1) and 14c(2), ordnance maintenance only; FM 23-40 para 7f(4) restricts barrel removal to authorized ordnance personnel. Done only to replace the barrel; the TM gives no assembly steps.

Applies to: M1928A1

Follows TM 9-1215 Ordnance Maintenance: Thompson Submachine Gun, Cal. .45, M1928A1 — War Department, para 14c(2)(b) (p. 19) archive.org [8]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  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.
    TipA pipe wrench may be used only if the barrel is to be scrapped.
    Removed at this step: Barrel
  5. To move the front sight and compensator to a new barrel, drive out the front sight pin.
    TipTM para 10c(1): do not remove compensator or sight unless necessary.
    Removed at this step: Front sight pin
  6. Drive the front sight rearward off the barrel.
    Removed at this step: Front sight
  7. Unscrew the compensator with a strap wrench.
    Removed at this step: Cutts compensator

Reassemble the box and drum magazines

Detail Reassembly

The FM gives no separate magazine assembly steps; para 8 says groups and their components go back together in the reverse order of removal, which is what these steps are.

Applies to: M1928A1

Follows FM 23-40 Basic Field Manual: Thompson Submachine Gun, Caliber .45, M1928A1 (with Changes 1–4) — War Department, para 8 (p. 8) archive.org [7]

  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.
    WarningKeep the spring covered with your fingers so it cannot fly out.

Reassemble the bolt group

Detail Reassembly

FM 23-40 para 8b.

Applies to: M1928A1

Follows FM 23-40 Basic Field Manual: Thompson Submachine Gun, Caliber .45, M1928A1 (with Changes 1–4) — War Department, para 8b (p. 9) archive.org [7]

  1. If the extractor was removed, slide it into place, lifting its head only enough to clear the stud.
    WarningAvoid excessive pressure on the extractor.
  2. Insert the firing pin and firing pin spring in the bolt.
    WarningDo 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

Detail Reassembly tools required

FM 23-40 paras 8 and 9: reverse order of removal; before the groups go back into the gun, the ejector must be screwed all the way home and the breech oiler must be in place.

Applies to: M1928A1

Follows FM 23-40 Basic Field Manual: Thompson Submachine Gun, Caliber .45, M1928A1 (with Changes 1–4) — War Department, para 9 (p. 9) archive.org [7]

  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.
    WarningKeep 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

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.
    WarningConfirm the latch is engaged before handling the weapon further.
  4. Cycle the action several times and perform the function check.

Torque specifications

No sourced torque values from the manufacturer are recorded for this firearm. Where a fastener has a specified torque — action screws, scope bases, muzzle devices, barrel nuts — get it from the manufacturer or a gunsmith rather than estimating it.

What the manufacturer does say: 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))

Materials and factory finish

As stated by Auto-Ordnance. Prep, masking and cure depend on these; a polymer or aluminium part, a nitrided or anodised finish, and a blued steel part are each a different job. Variants with other finishes may exist — check the maker's page for the exact SKU on the bench.

ComponentMaterialFactory finishWhere it comes from
Receiver
Thompson 1927A-1, T1 models		steelblued
Auto-Ordnance's current semi-automatic reproduction, not an original submachine gun.		Thompson 1927A-1 — Overview and Specs (Auto-Ordnance) — Auto-Ordnance (Kahr Firearms Group) auto-ordnance.com [5]
“The Tommy Gun is available with a blued steel receiver (T1 models) or a lighter weight aluminum receiver (T5 models).”
Receiver
Thompson 1927A-1, T5 models		aluminum—
Auto-Ordnance's current semi-automatic reproduction, not an original submachine gun.		Thompson 1927A-1 — Overview and Specs (Auto-Ordnance) — Auto-Ordnance (Kahr Firearms Group) auto-ordnance.com [5]
“The Tommy Gun is available with a blued steel receiver (T1 models) or a lighter weight aluminum receiver (T5 models).”
Stock
Thompson 1927A-1 (T1)		American Walnutpolished
Auto-Ordnance's current semi-automatic reproduction, not an original submachine gun.		Thompson 1927A-1 — Overview and Specs (Auto-Ordnance) — Auto-Ordnance (Kahr Firearms Group) auto-ordnance.com [5]
“The fixed stock is crafted in luxurious polished American Walnut and has a vertical foregrip.”
Whole firearm
Thompson T1-C Commando		steelparkerized
The maker states this for the firearm as a whole, not for a named part. Auto-Ordnance's current semi-automatic reproduction, not an original submachine gun.		Thompson 1927A-1 — Overview and Specs (Auto-Ordnance) — Auto-Ordnance (Kahr Firearms Group) auto-ordnance.com [5]
“The Thompson T1-C “Commando” model features parkerized steel and all wood stock, rear grip and horizontal foregrip in a durable black finish.”
Frame and receiver
Thompson M1 (TM1 steel / TM1C aluminum alloy) — semi-auto M1A1-style		solid steel or aluminumblued steel or black anodized aluminum
Auto-Ordnance's current semi-automatic reproduction, not an original submachine gun.		Auto-Ordnance (Kahr Firearms Group) — — Auto-Ordnance (Kahr Firearms Group) auto-ordnance.com [6]
“The frame and receiver are milled from solid steel or aluminum, the wood is genuine American walnut, and the overall finish is a blued steel or black anodized aluminum.”

Parts list

Transcribed from the manufacturer's parts list (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, p. 7 archive.org [4]) — Part I "List of Components of Thompson Submachine Gun Calibre .45" (numbered 1-38, keyed to Plates II-III) covering Models 1921 and 1928. Unnumbered magazine (XX, L, C) and sight component lists on pp. 8-9 not transcribed.. Key numbers refer to the exploded view in that document.

38 parts
KeyPartPart no.QtyGroup
1Actuator
These parts of model 1921 do not interchange with corresponding parts of model 1928.		1
2Barrel1
3Bolt1
4Breech Oiler (including Felt Pads)1
5Buffer (including Fiber Discs)
These parts of model 1921 do not interchange with corresponding parts of model 1928.		1
6Buffer Pilot1
7Disconnector1
8Disconnector Spring1
9Ejector1
10Extractor1
11Firing Pin1
12Firing Pin Spring
These parts of model 1921 do not interchange with corresponding parts of model 1928.		1
13Fore Grip1
14Fore Grip Screw1
15Frame1
16Frame Latch1
17Frame Latch Spring1
18Grip Mount1
19Hammer1
20Hammer Pin1
21Lock1
22Magazine Catch1
23Magazine Catch Spring1
24Pivot Plate1
25Rear Grip1
26Rear Grip Screw1
27Receiver1
28Recoil Spring
These parts of model 1921 do not interchange with corresponding parts of model 1928.		1
29Rocker1
30Rocker Pivot or Fire Control Lever1
31Safety1
32Sear1
33Sear Spring1
34Sear Lever1
35Sear Lever Spring1
36Trigger1
37Trigger Spring1
38Trip
These parts of model 1921 do not interchange with corresponding parts of model 1928.		1

Function check

After every reassemblyPerform these checks on a verified-unloaded firearm. If any check fails, the firearm is not safe to fire — stop and see a licensed gunsmith.

Maintenance

Lubrication points

Cleaning notes

A .45 ACP blowback fouls heavily. Clean the bolt face, receiver interior, and actuator track regularly. Surplus ammunition of this era is frequently corrosively primed. After shooting it, flush the bore, bolt face, and gas system with hot soapy water or a water-based solvent the same day, dry completely, then oil. Keep the firing pin channel clean and dry — a pin held forward by congealed cosmoline causes slam fires.

Suggested inspection interval: roughly every 1000 rounds. This is a general guideline, not a manufacturer specification.

Wear parts to inspect

Recoil spring and buffer · Extractor · Blish lock (M1928) · Magazine and drum springs

Common issues

SymptomLikely causeWhat to do
Looking for an H-piece that is not thereM1 and M1A1 Thompsons are straight blowback with no Blish lockIdentify your pattern. They are different weapons internally.
Drum will not feed reliablyDrum not wound correctly, or a tired drum springFollow the winding procedure for your drum. Drums are more finicky than box magazines.

Also covers

The procedures above are reported to apply to: M1928A1 · M1 and M1A1 Thompson (no Blish lock) · Semi-automatic Auto-Ordnance Thompson reproductions (with significant differences). Verify against the manual for your specific model.

Similar manual of arms

Legal notes

Not legal adviceSelect-fire Thompsons are machine guns under U.S. federal law and are heavily regulated in most jurisdictions. Semi-automatic reproductions are regulated differently. This entry documents maintenance only — know the law that applies to your specific weapon.

Sourcing

Confidence
medium — Drawn from reliable secondary sources and consistent across references, but not confirmed against a primary source.
Verification
Checked against an armorer/technical manual
Last updated
2026-10-29

References

Every source this page draws on, with its web address so you can read it yourself. Numbers in brackets elsewhere on the page point here.

Notes: The M1928 and the simplified M1/M1A1 differ materially — Blish lock versus straight blowback, top versus side actuator. Semi-automatic Auto-Ordnance reproductions differ again, with a closed-bolt action and a different bolt. Identify what you actually have before ordering parts. Field strip corrected on 2026-10-03 against FM 23-40 paras 6c, 6e and 9a: the lock comes out of the actuator, not the bolt; the frame-withdrawal caution and the lock orientation are added.

Found something wrong? Corrections are the most valuable contribution to this project. Open an issue with the model, the step, and a source.