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Question on Keystone marking on M1 Thompson


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#1 Buickman58

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Posted 30 July 2022 - 07:35 AM

I have searched and can not remember this silly question. Which manufacture stamped the Keystone outline on the front of the nose on Thompson receivers? Asking from something I saw and snapped no pictures, just cant remember.
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#2 Countryboy77

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Posted 30 July 2022 - 11:27 AM

On Ar15s its Cerro who uses the keystone mark
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#3 Buickman58

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Posted 30 July 2022 - 12:51 PM

Thanks, it was driving me crazy. Kahr makes the Thompson tribute guns, a friend was talking about them and could not think of the maker.
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#4 benedw60

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Posted 30 July 2022 - 04:02 PM

Bob from Philadelphia ordnance did it for a few runs back in the early days
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#5 Bridgeport28A1

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Posted 30 July 2022 - 08:47 PM

I have a Reconbob (Philadelphia Ordnance) produced milled grip mount that is stamped with a Keystone. I believe they were a single production run item.

Attached File  E5BF39DD-AAED-47C5-A8B5-3990E570CA41.jpeg   94.15K   4 downloads

The Cerro forge marking is usually described as a keyhole.

Edited by Bridgeport28A1, 06 August 2022 - 10:10 AM.

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#6 Buickman58

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Posted 02 August 2022 - 05:54 AM

Sorry took me a long time to get a picture, I cant own all but never seen this one.
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#7 Buickman58

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Posted 02 August 2022 - 05:56 AM

Of course cant figure out how to attach it

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#8 reconbob

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Posted 03 August 2022 - 10:10 PM

     Way back in the 1980s I briefly marked the 80% receivers with a Keystone to identify them as Phila Ord. It did not last long because just about everybody asked if they could get a receiver without the Keystone.

Bob/Phila Ord
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#9 Countryboy77

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Posted 03 August 2022 - 11:47 PM

Where did you mark them Bob?
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#10 Buickman58

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Posted 04 August 2022 - 05:11 AM

Hello Bob,
Thank you for the help, and nice to know. I often get pieces to make display guns and a friend was taking some lend lease parts off one of your older receivers it looks like. I remembered seeing your mark(I believe) on some bolts a bit back. Nice workmanship on the 80%!
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#11 reconbob

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Posted 04 August 2022 - 09:14 AM

   If I recall I marked the receivers on the left side in front of the magazine cutout. I dont remember marking the front like the one in the photo but its so long ago I cant be sure.

  We make M1A1 Thompson bolts to GI specs and to distinguish them from original bolts they are marked with a keystone on the rear face of the bolt body.

Bob
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