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Trouble Shooting M1 Safty Going On When Shooting


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#1 JTinIN

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Posted 24 October 2004 - 11:19 AM

Was able to take my "in-transfer" M1 out to the range yesterday to shoot for the first time, had great day shooting in the rain (covered firing line) with my SOT/friend, which also included a case of ammo in a nice BAR FN-D and various new "stuff". Had only two issues, first had to leave the "in-transfer" M1 TMSG with my SOT when the two of us were done shooting (the TMSG was stripped, cleaned and oiled while the wet MP5 was in the truck ... have to set priorities (the MP5 did dry well after running a beta mag through it ... and was stripped, wiped and covered in light CLP for a real cleaning today ;-)

The second issue was during the several hundred rounds fired the safe/fire selector would ever so often move down enough to keep the gun from firing (shooting may two and three round bursts) until I pushed the selector back up a little.

Checked and the "spring" (aka pivot plate) appears in the slot however the selector for safe/fire is not that firmly in the fire posistion. While waiting on the paper work the SOT and I will be talking everything apart to check (he knows his way around a TSMG a little bit, owning several and having built a receiver from scratch on a Form 1 in the good old days), but would like to check with the knowledge base hear for my own educiation on what to watch for when trouble shooting.


Assume the tree areas to check are:

1:The safe/fire slector where it contacts the pivoit plate and any of the internal firecontrol parts (assume there is a ramp/detent to provide the force to keep the slector on fire).

2: The force of the external "spring" (aka piviot plate) - any field checks on the force of the flat spring that contacts the selector etc.?

3:What ever internal fire control surfaces contacts the selector

4: Everything else that I do not know enough about (probable the best answer for the typical question on repairs is "if you do not know than send to the experts such as P.K. .... smile.gif


Thanks again for everyone inputs and ideas.

Edited by JTinIN, 24 October 2004 - 02:31 PM.

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#2 Chopper28

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Posted 24 October 2004 - 11:29 AM

Start with the simple stuff first. Replace selector, sear, and pivot plate. Do one piece at a time trying the gun after each replacement. Hopefully this will solve the problem. Also check the bolt surface where it engages the sear. There are not that many things involved that could be causing your difficulties. Also check or replace the recoil spring. These are all relatively inexpensive repairs. If that does not fix it, call PK. Just my .02
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#3 JTinIN

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Posted 24 October 2004 - 12:10 PM

QUOTE (Chopper28 @ Oct 24 2004, 11:29 AM)
Start with the simple stuff first. Replace selector, sear, and pivot plate. Do one piece at a time trying the gun after each replacement. Hopefully this will solve the problem. Also check the bolt surface where it engages the sear. There are not that many things involved that could be causing your difficulties. Also check or replace the recoil spring. These are all relatively inexpensive repairs. If that does not fix it, call PK. Just my .02

Thanks, appreicate the ideas and check list. Always like to use the initial trouble shooting to learn what is going on the fire year or so, helps a lot later down the road when your local RKI is no longer around.

Took the M1 down at my SOTs when first started to pruchase it (always like to check for welds and other "features' on the inside), the recoil spring is nominally ok condition (was in a larger collection that has not been fired for many many years ... ).

What do you recommend for a recoil spring?
1:NOS (if any are round)
2: After market - Wolf Gun Springs for Thomson Stock No. 85251
THOMPSON 1928 M1, .45 RECOIL SPRING - extra power. Improves reliability and functioning. Stock No. 85251.....$ 10.99 ea
3:Good conditon used?

North Ridge Thomson Items
IMA USA Thomson Parts
SARCO Inc. Thomson Parts

Keystone Arms Thomson Listings

Was also talking to Brickyard off line and had not even though of once get the issues worked out, can check for parts with the correct in patina to match the gun (the newer guns all come in Black or Colt early Gray .... no class smile.gif .

Edited by JTinIN, 24 October 2004 - 02:48 PM.

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#4 PK.

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Posted 25 October 2004 - 08:18 AM

I would bet your problem is in the interface of the pivot plate leaf that tensions the safety and the safety detents machined into the groove that accepts the leaf.

The detent holes machined into the safety can wear on the edges and allow a few degrees of free rotation of the safety. If this is the case, replace the safety.

If the detent holes look OK (with sharp edges) and are deep enough, it could be that the male protrusion on the end of the leaf that engages these detents is worn. This is the middle “bump” you see. This can be reshaped with a file in most cases.

If the spring tension is weak, the spring can be carefully re-bent to restore a proper load.

When everything is right, the safety should snap into position and not move without biasing the spring leaf.

With the frame removed from the receiver, it is easy to see how the safety engages the sear. A bevel can be ground into the leading corner/ edge of the safety where it engages the sear if required- this is unusual.

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