Early MGC Thompson M1921... C.P Conversion

Post by Phil_D

I received some CP rounds for my open barrel Thompson today thanks to Shazhib and started to measure the old chamber and firing pin....


It was evident there was only a slight difference in the size of rounds and the paper cap firing pin was 4mm to short and 2mm too wide...
Had a quick rummaged around and some of the older members here will remember the 3 pin round mains plugs we used to use, well the earth pin was an ideal shape and had the correct thread on it and this was quickly turned down in the lathe and fitted into the Thompson....

Loaded up some rounds, bang bang bang in single mode switched to full auto and squeezed the trigger it was loud and the smoke was pouring out the barrell
Not bad for a 7 minute conversion, i will make a new pin from steel when i get some more time but to be honest i dont see the need to buy or make a new chamber at this stage.
On a side note the original rounds were very dull....you can see a new one in there for comparision

A quick ultrasonic clean in a weak ammonia solution produced this result...

Cheers all
Phil

Post by shazhib

Phil_D,

If you not be bothered, use "steel wool" to polish outside the rounds, it makes the rounds lot cleaner.....while it makes your hands lot dirtier.

Post by Claymore

Well done mate nice easy conversion i never would of thought of the mains plug. wonde if that could be used for anything else det wise.

That's a nice and ingenious solution mate, well done!

If you have a lot of brass rounds and you fire them regularly and in quantity, it might be worth investing in a Lyman Brass Case Vibrating Tumbler polisher.
I bought one from a local gunsmith for £70 including a husk based polishing powder that's reusable (for ever by the look of it).
Once the cartridges have been washed in the Ultrasonic with hot water and washing up liquid, I just chuck all the parts into the polisher, switch on and leave it for a couple of hours.
They come out gleaming, both outside and more importantly, inside too.

Best £70 I spent yet.

Cerwyn
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Hobby collector of mainly WW2 era uniforms, headgear, field equipment and replica weapons.

Post by Phil_D

The brass plug pin is not really hard enough but for a test its quick and easy to machine and will provide a template for a harder steel version.
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Too many to list now and the collection has stopped still growing.