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Punisher
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PostSubject: mgc 1921 restoration   Sat Aug 05, 2017 3:27 am

Just picked up a mgc 1921 Thompson. It is missing the stock. Came with 1 magazine with no markings. The wood has a nice old look with very few dents and no worn finish. The bluing is very worn.






It looks like a pin is in the end of the muzzle. The chamber is plugged and the head of the screw holding the plug in is broke off. From what I found online I should be able to remove the screw under the chamber. Then the plug can be removed and replaced with a chamber and detonator for plug fire cartridges. I have a lathe and can make a new chamber and detonator. Does anyone have drawing or dimensions?





The bolt face is uncut. The extractor is missing the hook to catch the cartridge. Should be able to either make a new one or rework the original.


I found real Thompson wood can be made to fit. I am missing the complete stock. Mgc stocks are missing the cross bolt so would like to have the real stock. Has anyone tried fitting the metal part of a real Thompson stock onto the mgc?

Found the real Thompson magazines can be made to fit. The feed lips are different and the catch hole is in a different location. Don't have a real magazine yet to compare to. Is the only thing needed is to cut the feed lips and make a new hole for the catch or is there more to it?

For the restoration I want to keep the finish on the pistol grip and fore grip as long as it matches the stock. For the metal parts all the mold lines and inperfections will be filed and sanded down, then reblued.

Tried rebluing part of the receiver. It turned out a nice dark almost black blue.
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PostSubject: Re: mgc 1921 restoration   Sat Aug 05, 2017 1:30 pm

Thanks for posting up your project!  Please keep us informed of your progress!

I'll try to add a few thoughts, for what its worth, to address some of your questions.

It looks like you have an "import" model, which is why the bolt is non-functional, the chamber is blocked, and the upper receiver area has a small section milled out.

What I think is good news for you, is that it is a model made sometime before 1978, which means it has an "open" barrel.  That means that if you return it to a firing model, it will vent smoke from the front of the barrel.  Models made after 1978 had fully blocked barrels.  I much prefer the older models because of their ability to vent.  

Chamber - I've seen these slugged and pinned in a couple different ways over the years - all can be reversed if you are mechanically inclined and if you own machinist tools, you obviously must be.  The chamber plug will have a recessed groove that the pin sets in to retain the plug in the receiver.  If you remove the pin, the chamber slug can be removed.  The threads for the chamber retaining screw have not been machined into the receiver any of the blocked models I've seen in the past.  You will likely have to cut threads and install a chamber retaining screw.  Some plugs are a pain to remove, but since you have an open barrel, you are on easy street as it can be driven out by inserting a rod or tool from the muzzle end.  

I don't have the dimensions for the chamber/detonator, but someone on the forum probably does.  I recommend vent holes in the base of the assembly if you're going to "fire" this model, since it will vent smoke from the barrel.

As far as returning it to firing, you should also consider fabricating a recoil spring buffer (rubber piece at the end of the recoil guide).  As an import model, yours will not have this piece.

The bolt- looks like you would also need to machine the face of the bolt you have.  At least it hasn't been cut at an angle, like most were.  The extractor is a fixed piece on this type of bolt and really was improved with the later versions which involved a spring design.  

You probably have an original MGC mag.  They had no markings.  The shape of the lips compared to a real mag are quite different.  As you mentioned, the locking lug hole will not be in the same spot.  I believe you will find that a real mag is also too wide in the spine area.  This can be remedied by modifying the receiver slot or the mag spine.  There are variations in MGC receivers and also variations in real mags, so it's kind of a situation where you might have to fit each one individually.  Getting this old model to work 100% with the stick mag usually requires some fitting to get it feeding just right in my experience.


The MGC Thompson was a very popular model and it still is today.  Because of this, parts can still often be found if you need them -  Bolts, chambers, cartridges, etc.  Some forum members here have helped many of us out with items only found overseas. This is a great forum and you've come to the right place for modelgun info.

Best of luck with your restoration!
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PostSubject: Re: mgc 1921 restoration   Tue Aug 22, 2017 1:56 am

Picked up a denix Thompson to see how it compared to the mgc. It is similar but made simpler.

The bolt is cut at an angle and missing the extractor. There is an outline of where the extractor would be. The denix spring is smaller. A mgc bolt and spring does fit in the denix. It is a little tighter fit than in the mgc receiver but still plenty of room to operate.






The denix stock slide rails are a little wider. The denix safety and selector are molded with the lower. It only has a trigger and sear. The grip is shaped different and held on by two screws from the top under the sear. The mgc stick mag doesn't fit the denix. A denix drum is supposed to fit a mgc. Might work the other way around too. The magazine release is held on by a screw.





The sight base on the denix is molded with the receiver. The sight does flip up but not adjustable. The denix doesn't have an ejector. The barrel two pieces and removable. It is partially hollowed out. To remove the barrel clamp the front in a vice. Tap on the other half of the barrel. It comes out pretty easy. The screw for the foregrip can then be removed. Clamp the rest of the barrel in a vice and tap the receiver. The hole in the receiver is a little over 3/4" There are no feed ramp but material is there to make it. The horizontal foregrip is only good for firewood. They decided to round off the front and back of the foregrip. From some comparison pictures I found the vertical forgrip is shaped wrong too. It looks like there is enough wood there to reshape it to look right.




The denix stock is held on by a wood screw through the top of the receiver and through the lower. The front of the lower is held on by wood screws from the bottom. Will drill and tap for socket head allen screws to go from the bottom.

Decided to try making the denix stock fit the mgc. Found a 3d printable model of a Thompson. https://www.myminifactory.com/object/thompson-1928-sub-machine-gun-functional-assembly-16060
Printed out the stock slide, catch, and button. Made a pin from the shank of a bolt. Used a coil spring under the catch. The inside of the denix stock needed to be cut out to fit the slide. Needed to file down the rails on the slide to fit the mgc lower. Only had white pla so it is hot glued in place for now. The stock fits solid and slides on and off easily. Will reprint in gunmetal gray abs. The slide is supposed to be held on by two screw through the bottom of the stock. Not sure how well the abs will hold being tapped. Might just epoxy in place and add fake screw in the bottom. After looking at some pictures the stock needs to be sanded down to match the shape of the tang of the slide.


The sling loop is screwed on with small round head wood screws on top of the stock. I inletted it and used some flat top slotted wood screws. The plate did not match up with the stock and held on by small round head screws. Filed down the spots that were bigger than the stock. Then sanded the stock to match the rest of the plate. Found some bigger flat head wood screws. Counter sunk the holes for the screws. Sanded down and blued all the metal. Sanded the finish off the stock and put on some dark stain. The stain looked close to the mgc wood. When I went to put some tung oil on the stain started to come off. Rubbed on some used motor oil. It got a little darker but still doesn't match.





Found that auto ordnance used mgc stock slides when they ran out of real Thompson slides. Several people have mentioned that the stocks are wobbly because of the differences in dimensions. Apparently the mgc slide will fit a real lower but not the other way around. The mgc is wider.
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PostSubject: Re: mgc 1921 restoration   Mon Sep 04, 2017 10:08 pm

On the mgc got the parting lines on the fins of the barrel cleaned up. Drilled out the bottom screw that holds the plug in place. Need to get a new chamber insert and rework the extractor. Then it should be ready to fire.




On the denix replaced the foregrip bar that is attached to the barrel with a steel one. Took a piece of 1/4" flat bar and cut it to a 1/2" x 7" strip. Rounded off the ends. With a debur bit in a dremel cut 1/2" wide slot 1/4" deep on the bottom of the receiver. Drilled and counter sunk for two 10-32 screws. Drilled 1 hole in between for a 10-32 allen set screw. That screw will go into the barrel and push against the chamber to hold it in place. Cut the foregrip bar off the barrel. Put it in a lathe and cleaned up the fins. Turned down the front sight for a compensator to fit.




Drilled a hole and tapped for a 10-32 bolt where the ejector is molded on the receiver. Sanded off the molded ejector. Will cut the head off a bolt and weld on a piece of 16ga and shape to look like the ejector. This part will only be to make the receiver look more realistic. Will make a ejector that goes in the magwell like the mgc.



Cut down the metal in front of the magazine to make a feed ramp. Made it look like the mgc. Might need to adjust it later when the chamber is installed.



Opened up the slots on the lower for a mgc mag to fit. The mag slides in now but the hole to lock it in place is too low. Will modify a real mag to work.



The hole in the rear of the receiver is the right size to tap for a 10-32 bolt. The hole in the lower wasn't centered. Drilled it a little bigger so that it would be centered. With a dremel cut out for a socket head screw to fit flush.

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PostSubject: Re: mgc 1921 restoration   Tue Sep 05, 2017 7:40 am

sweet
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PostSubject: Re: mgc 1921 restoration   Tue Sep 05, 2017 9:40 am

Thank you very much for taking time to write this down in detail!


It's a good looking project, I'm looking forwards to seeing the finished product. 

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claymore
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PostSubject: Re: mgc 1921 restoration   Tue Sep 05, 2017 2:00 pm

Bloody good work mate, i would not even thought of doing this to a Denix, well done real nice work
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PostSubject: Re: mgc 1921 restoration   Sun Sep 10, 2017 2:22 am

Has anyone been able to repair the cut face of a bolt? I have a few ideas how to do it but would like to know if anyone has tried before.

Option 1 is to cut off the round part of the bolt. Then bore a hole through the rest of the bolt. Make a new head and somehow attach it. There isn't much material on the back half. Probably not enough for a pin. Maybe it could be threaded or soldered on.

Option 2 is to cut off just behind the slanted head. Drill a hole partway into the bolt. The new head would have a narrower back to slide into the hole in the bolt. There is more material so it could be pinned, threaded, or soldered on.

Option 3 is to somehow build up the bolt face with some kind of material. Possibly solder or jb weld. Not sure how permanent of a fix it would be.

Thinking of trying option 2 first. On a lathe make a jig that slides over the round part of the bolt and has a center hole long enough to guide a drill bit. Will try soldering with some solder for pot metal first.

If anyone can think of a better way let me know.
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PostSubject: Re: mgc 1921 restoration   Sun Sep 10, 2017 8:22 am

hi, don't think you can weld spelter ( zinc based )

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PostSubject: Re: mgc 1921 restoration   Sun Sep 10, 2017 10:37 am

Making a steel bolt might be the easiest way to tackle the problem. You could contact forum member 8ace about this as he's made steel replacement bolts for a number of us over the last few years.

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PostSubject: Re: mgc 1921 restoration   Tue Sep 19, 2017 1:14 am

Got a new steel chamber for the mgc. Got 2 20 round stick mags and a 50 round drum. They are for the new manufactured thompsons. The drum does fit the mgc but is pretty loose. The bent sheet metal rail that hold the front of the drum in place would need to be cut off and have a plate welded in between the rail and the drum to make it a tighter fit. The stick mags fit in the slot good but the catch hole is too low. Would need the hole enlarged to work. The feed lips are bigger but can be cut down. Waiting on cartridges to see if they will feed without cutting the mag.
mgc top original Thompson bottom

original Thompson left mgc right


Drilled a hole in the denix barrel for the chamber. Then used a carbide cutting bit in a dremel to enlarge the hole so a mgc chamber will fit. The hole is a little rough but a set screw will hold the chamber in place.



Made a new bolt face for the denix bolt. A 5/8" steel bolt is the right diameter. Cut the head off and squared off the face in a lathe. Then used an end mill to cut the recess in the face. On the back side turned down a 1/2" section to 1/4". Cut off the face of the denix bolt and drilled a hole in the center. Put the new head on the bolt and clamped it in place. Took a cutoff disk on a grinder and gouged out a little around the seam for soldering. Used super alloy 1 solder from muggy weld. Roughed out the slots with a cutting disc on a grinder and finished with a file. Need some cutting discs for a dremel to finish the ejector and extractor slots.




Got some wood filament to print out the fore grips, pistol grip, and stock. I printed the parts so the layer lines go the same direction as the wood grain is supposed to. Found a program that can randomly change the temperature of the extruder at different layer heights. The hotter the extruder gets the darker the wood is supposed to get. It is supposed to look more like real wood by having different color layer lines. With the filament I used it didn't turn out. Printed the parts with a thin outside and mostly hollow to see how they would turn out before making some solid ones. With the foregrip printed I marked the end on the grip bar and cut it to length. Then used the hole in the grip to drill for the screw. The 3d files I used are a little different shape than the mgc wood. The parts that are printed solid can be filed and sanded to change the shape to get it a little closer.





Picked up some rustable magnetic iron filament from proto-pasta. https://www.amazon.com/Proto-pasta-FEP11705-Rustable-Magnetic-Spool/dp/B00X8BQYPS/ref=lp_10615202011_1_2?srs=10615202011&ie=UTF8&qid=1505778811&sr=8-2 It is pla plastic mixed with powdered iron. Printed out a compensator. Had to scale the length and width to match the mgc compensator. With some course steel wool polished it to expose more of the iron. It didn't blue as dark as the zinc but still turned out good. Turned down the end of the barrel so the compensator would slide on. Used some 5 minute epoxy to hold it on.




For the front lower screws drill and tapped for some 8-32 slotted screws. Then counter sunk the lower for the screw heads. Used some super alloy 1 solder to fill in the top of the rear hole. The solder is zinc based and can be blued.



The stick mags do fit the denix after the slot is opened up but the catch hole doesn't line up. The drum does fit and barely wiggles. Think the drum will be for the denix and the stick mags will be for the mgc.
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PostSubject: Re: mgc 1921 restoration   Tue Sep 19, 2017 2:15 pm

cool project, wont a real Thompson bolt fit ?, as your in usa very easy to find
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PostSubject: Re: mgc 1921 restoration   Wed Sep 20, 2017 11:49 pm

A real m1928 bolt is 3 pieces. The main bolt body, actuator that is the bolt handle and the recoil spring goes into, and a lock to connect the two together. Can get a stripped bolt body for $50, but adding the actuator, lock, and extractor starts getting expensive.

I found a 3d file for a m1928 bolt that is supposed to be modeled to scale off of original drawings. It is a little wider than a mgc bolt. Planning on printing it out and seeing what changes are needed to make it work.
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