M1 Bolt and Sear connection

[JEB007x]

Group,

I hope I am posting in the correct Forum.  I am a newbie to Thompsons.  Attached are 2 pictures.  It appears the front of the bolt has a slight Ridge very small but can feel with it with my fingernail.  The opposing Sear? has the same sort of edge.  You can see the wear on the lower.  Should I replace the sear / bolt?  I cannot feel it when I cycle the gun, (i have not shot it yet)  Thanks in Advance.

[Motorcar]

Welcome and congrats on the M1. Yes you found the right forum.

That is just a bunch of rounds and 80 years of being in that gun you see there. Firing open bolt and chugging like a freight train doesn't require the fine sear/trigger pull of a Camp Perry competition. You could dress it with a file if it bothers you, or replace both, but it wont change how the gun runs. There is no danger of it dropping out and firing inadvertently, that sear and bolt notch is huge by some comparisons.

There might be a purist that says it must have new parts to be "right" but it's really not an issue.

[JEB007x]

Motorcar... Thanks for the input.  Glad there is no danger of it having fire inadvertantly.  Will shoot as is!!!  Thanks again.

[reconbob]

  Thompson bolts and sears are very hard. Over Rockwell 60C. That is so hard a file will skid right off. While there is no danger here, I would stone the little ridges off so that the engaging surfaces stay smooth.  At the minimum I would replace the sear, which might be $25. If you can afford it I would also replace the bolt.
  This wear is not normal. I have seen many many WW2 Thompsons that have many thousands of rounds thru them with the only wear being the loss of bluing. No deformation ridges as in your photo.

   In your first photo the loss of bluing on the trigger frame behind the sear is the result of the deformed ridge of the bolt scraping on the trigger frame which is not hardened and softer than the bolt.

    There is no way of knowing for sure why your bolt is deforming. Faulty heat treatment 80 years ago? Was the bolt exposed to heat somewhere along the way affecting its hardness? 
 

  Another thing - when you shoot a Thompson you must fully and decisively pull the trigger. If you sloooowly pull the trigger to fire single shots the sear drags on the bottom of the bolt and the bolt will just nick the sear encouraging this deformation. If you want to fire single shots set the selector to single, and fully and decisively pull the trigger.

Bob

   

[TD.]

JEB007x,

Welcome to the Thompson forum! 

Is your Thompson an Auto-Ordnance Corporation, West Hurley, New York, M1 Thompson submachine gun. 

Can you post complete picture of the underside of the bolt? 

[Frank I.]

Quite common...too much semi-auto firing...its a MACHINE gun 😁

[reconbob]

Frank - I respectfully disagree with you rating this bolt damage/deformation as "quite common". I have had hundreds of Thompsons thru my shop for builds or repairs and almost never see this deformation.  Years back I processed 900 used, torched Thompsons (Sarco project. This was long before 1986 and they wanted to reweld/build them into guns). The bolts were torched but the sear notches were intact and there was thought of rebuilding them. None of the bolts had this damage/deformation. I have bought and sold hundreds of used bolts and this damage is so rare (if it is military bolt) as to not exist.

I am willing to be educated/corrected. Anybody who reads this and is willing to take the time, check your Thompson bolt and let us know if it has the damage/deformation shown in the photo above.

Bob/Phila Ordnance

[StrangeRanger]

If it's a WH gun it is not uncommon, my former WH 28 was almost exactly like that and the burr came off with a file no stoning required

Edited Wednesday at 05:23 PM by StrangeRanger
typo

[Motorcar]

14 hours ago, reconbob said:

Another thing - when you shoot a Thompson you must fully and decisively pull the trigger. If you sloooowly pull the trigger to fire single shots the sear drags on the bottom of the bolt and the bolt will just nick the sear encouraging this deformation. If you want to fire single shots set the selector to single, and fully and decisively pull the trigger.

 

3 hours ago, Frank I. said:

Quite common...too much semi-auto firing...its a MACHINE gun 😁

 

1 hour ago, StrangeRanger said:

my former WH 28 was almost exactly like that and the burr came off with a file no stoning required

JEB007x, let us know how it runs.

[Motorcar]

Here is my 85 year old '28, it exhibits the same wear pattern as the one in question though not as pronounced. Pictures with such close in definition give a detail the human eye doesn't generally pick up on. I have put thousands of rounds thru this one, how many went before me? How many could have gone down range in 8 decades on any of these? Runs like a champ and I drive the trigger like a dump truck, no finesse.

[laurencen]

any time you get deformation its worth stoning the burr, if left it will simply rub against another surface like the lower, the bolt is hard and will not clean up using a file, Im throwing it out the lower is not hardened to the same degree as the bolt if the burr is rubbing on the lower it will wear the lower over time

[Frank I.]

On 5/6/2026 at 12:34 PM, reconbob said:

Frank - I respectfully disagree with you rating this bolt damage/deformation as "quite common". I have had hundreds of Thompsons thru my shop for builds or repairs and almost never see this deformation.  Years back I processed 900 used, torched Thompsons (Sarco project. This was long before 1986 and they wanted to reweld/build them into guns). The bolts were torched but the sear notches were intact and there was thought of rebuilding them. None of the bolts had this damage/deformation. I have bought and sold hundreds of used bolts and this damage is so rare (if it is military bolt) as to not exist.

I am willing to be educated/corrected. Anybody who reads this and is willing to take the time, check your Thompson bolt and let us know if it has the damage/deformation shown in the photo above.

Bob/Phila Ordnance

Hi Bob,

Perhaps it's a case of civilian VS military use, as well as 80+ years of shooting as opposed to 20 or so years of military service?  

There is no doubt that you have observed many more Thompsons than I but, but I have seen burrs on the sear surface of the bolt that gouged the trigger frame. (as depicted in a photo in one of the threads above)

When I bought my first Thompson, a knowledgeable and respected enthusiast advised me to watch for 1. dress burrs on the bottom of the bolt, 2. always hold the button down when installing and removing a '21 or '28 buttstock assy and 3. always wipe down rear part of the grip where the web of your hand touches.   

Respectfully, 

Frank

[JEB007x]

Gents,

Thank you for all the feedback.  I have not checked the forum as I was away visiting my Mom!  I am always getting spare parts so I have picked up an M1 and M1A1 bolt.  Need to get a sear.   I will probably fire her as is, very soon.  I am going to submit several other photos and would love general feedback on your observations on the overall condition.   Most is S, savage marked.  Thanks.. this fourm is very helpful.

John

[JEB007x]

On 5/6/2026 at 9:19 AM, TD. said:

JEB007x,

Welcome to the Thompson forum! 

Is your Thompson an Auto-Ordnance Corporation, West Hurley, New York, M1 Thompson submachine gun. 

Can you post complete picture of the underside of the bolt? 

Auto Ordinance

 

[rpbcps]

Could this be a mismatched M1?

A subtle difference between AOC and Savage produced weapons is found on the trigger frame. The selectors on Auto-Ordnance Corporation Bridgeport produced Thompsons are marked, ‘full auto’ on one single line, while on Savage manufactured Thompsons, ‘full auto’ are stamped in two lines, if I recall correctly?

If I am reading the AIO stamp on the receiver correctly, I see 'GHD'. Those being the initials of Colonel Guy H. Drewery, who was the AIO at the Auto-Ordnance Bridgeport plant.

 

Edited 4 hours ago by rpbcps
Typo

[rpbcps]

Just remembered, this topic is in the reference thread pinned post.

www.machinegunboards.com/forums/index.php?/topic/20691-identifying-savage-and-auto-ordnance-bridgeport-manufactured-thompsons