Thompson 1928A1 kit builds

[Cbod82]

1 hour ago, TD. said:

I would like to see a picture of the frame serial number. I don't care about the last 3 numbers. I believe S-406XXX may be the earliest frame I have seen with square magazine slots. 

As far as I know, all Thompson submachine guns provided to all allied forces during World War II were U.S. marked.  

Great info TD! thanks! I mistyped the frame serial earlier, it’s 496 not 406, but maybe still the earliest you’ve seen with the square mag slots? I’m really not one to be overly concerned with hiding non matching serialized parts, so here you are!

Really going to show my ignorance here, but what’s the story with the different style mag slots? I know the M1s can’t accept drum mags due to a design update. Is this what the square mag slot indicates?

Interesting thought about this one potentially having been issued outside of the UK, but like you said, between the mismatched parts and probable wartime replacement parts, it’s pretty hard to establish any sort of real provenance. Despite the thrown together nature of the kit, I’m extremely happy with the overall condition and solid presentation appearance! 

[Cbod82]

3 minutes ago, TD. said:

As a thought, after you remove the fore grip (with a properly fitting screw driver) for examination), get a good grip on the barrel (not with the grip mount) and see if it will turn off the receiver piece.

I will do that tomorrow morning for sure! Are you thinking because the index lines don’t match up there might be some play there? If it does turn out of the receiver, what is the method for properly securing the barrel on there? Pin?

[Cbod82]

10 hours ago, TD. said:

As a thought, after you remove the fore grip (with a properly fitting screw driver) for examination), get a good grip on the barrel (not with the grip mount) and see if it will turn off the receiver piece.

I’m still on the hunt for exact right size flathead so I don’t mar the screw at all. I just moved into a new house and can’t find a damn thing, haha

[ron_brock]

10 hours ago, Cbod82 said:

I will do that tomorrow morning for sure! Are you thinking because the index lines don’t match up there might be some play there? If it does turn out of the receiver, what is the method for properly securing the barrel on there? Pin?

Just torque.  You’d need a properly fitting barrel vise and fixture to hold the receiver nose.  Do not use a regular vise or any type of pliers/pipe wrench.  It’s better to be loose and/or non aligning than to bugger stuff up.  
 

Ron

[Cbod82]

21 minutes ago, ron_brock said:

Just torque.  You’d need a properly fitting barrel vise and fixture to hold the receiver nose.  Do not use a regular vise or any type of pliers/pipe wrench.  It’s better to be loose and/or non aligning than to bugger stuff up.  

Great advice Ron! I JUST received a versa vise I ordered on eBay that has barrel clamps. Should really come in handy with these types of projects once I get it out of the box and on my bench!

[StrangeRanger]

Pulling a Thompson barrel takes special tooling.  The vise has to fit the receiver exactly with nothing on the jaw surfaces that can mar it. The barrel wrench has to be able to grasp the barrel right at the receiver meaning it has to fit under the forend grip mount.  If you grab onto it further out you risk damaging the barrel

There are at least two gunsmithe on this board who have the tooling and expertise to do the job: Deerslayer and Got Uzi

Edited August 10, 2025 by StrangeRanger

[Cbod82]

6 minutes ago, StrangeRanger said:

Pulling a Thompson barrel takes special tooling.  The vise has to fit the receiver exactly with nothing on the jaw surfaces that can mar it. The barrel wrench has to be able to grasp the barrel right at the receiver meaning it has to fit under the forend grip mount.  If you grab onto it further out you risk damaging the barrel

Thank you! I’m not planning on pulling the barrel unless it ends up being overly loose and turntable by hand. I was more interested in possibly turning it into the receiver just a bit more so that the index lines match up. Just like with wanting to add the missing comp pin, I’m not sure if this would even affect function in a completed firearm, but it’s more of an OCD thing for me. When on display, I’ll always know these small details are just slightly off and it’ll drive me nuts!

[StrangeRanger]

The same tools and the same caveats apply when installing/tightening a barrel as when removing one.  do it wrong or use the wrong tools and you can trash the barrel and/or the receiver

[TD.]

Cbod82,

Given the location of the markings on the barrel collar, I thought it possible who ever installed the barrel on the front receiver piece may have just screwed it on hand tight. If the barrel is installed all the way, there is no way you will break it free by hand. And no way you will tighten it on the receiver piece correctly without proper tools. Given you are not working with a registered receiver or even a complete receiver, take care and do not damage the barrel. My thoughts are only a suggestion. Please don't play Superman with a pipe wrench!

You may also try removing the compensator by hand since it is not pinned. Again, don't force anything. It would be interesting to see if there is a compensator pin channel on the barrel boss that indicates this barrel had a pinned compensator installed in the past.

The fore grip will be much easier to remove. While the fore grip is off, look for a manufacturer marking on the grip mount as well as a mark inside the grip mount channel on the fore grip. 

You have a parts kit with a lot of nice parts. Enjoy learning on it versus an expensive transferable Thompson submachine gun.  

[bob241]

The barrel  mayl not screw off by hand,  it seems the first 4 fins in one of the pictures are showing slight damage from using some kind of wrench, or it just may be my old 88 year old eyes playing tricks on me.   

[Cbod82]

Thank you all for advice! I’m definitely not going to do anything to damage the kit, so no worries there! More just checking to see if any of the parts of the kit were put together by hand for a completed look, or if they were properly installed by an armorer. 
If the compensator isn’t attached to the barrel with a pin (pin missing), is it just screwed on like any other compensator? Is replacing the pin as simple as tapping a new one into place, or is there more to it than that? 
As far as any possible future need to turn the barrel in or out of the receiver (on any Thompson), does something like the index lines not matching up perfectly effect function or safety in anyway? Not talking loose, but maybe a mm or two off? I’m sure headspace is still a consideration, too. 

 

[bob241]

The index line on the receiver probably  will never line up with the index line on the barrel, as you have a replacement barrel , just remember, each turn of the barrel is  .100 inch, or ten turns  per inch your replacement barrel needs to turn a 1/4 turn so the P on the barrel lines up to the dot on the front of the receiver, and that would be  .025,  then your index line on the barrel will (you hope) will line up with the receiver index line.  None of your pictures show the barrel index line, only the P and the S . there also should be a very small 0 stamped in the gullet between the rear barrel collar and the first fin. 

[Cbod82]

1 hour ago, bob241 said:

The index line on the receiver probably  will never line up with the index line on the barrel, as you have a replacement barrel , just remember, each turn of the barrel is  .100 inch, or ten turns  per inch your replacement barrel needs to turn a 1/4 turn so the P on the barrel lines up to the dot on the front of the receiver, and that would be  .025,  then your index line on the barrel will (you hope) will line up with the receiver index line.  None of your pictures show the barrel index line, only the P and the S . there also should be a very small 0 stamped in the gullet between the rear barrel collar and the first fin. 

Thanks Bob! Here are some additional pics of barrel collar and front of receiver. I think this covers everything that can be seen without removing the vertical grip. Is the small 0 you’re talking about the one on top of the receiver, opposite the S on the barrel?

 

 

[Cbod82]

On 8/9/2025 at 8:27 PM, TD. said:

I find the fore grip interesting too. I suggest you remove it and see if there is a letter "S" inside the grip mount channel. If so, please post a picture. If not, probably a nice reproduction.

TD, finally got the vertical grip off. There is indeed a Savage S! While the serialized parts don’t match on this kit, I’m awfully fortunate that all the components are original!

[bob241]

Cbod 82 I sent you a PM (private message)  its the small black envelope top right

[Cbod82]

Bob, couldn’t send the pics on PM for some reason, so here they are. Best I can get with current lighting unfortunately.

[mgvince]

I keep looking at that compensator.  That looks like laser dross on the vent cut edges, not machined.  The whole thing looks too good.  
Maybe it’s just me. 

[TD.]

Cbod82,

Thank you for the frame serial number. It fits perfectly with known late Savage Arms frames with square magazine slots. 

You did great with the vertical fore grip. It appears you have a Savage Arms vertical fore grip. These are hard to find and expensive when found. Congratulations. I thought it might be a Savage fore grip but the angle at the rear of the fore grip was a little more than I am used to seeing. Of course, with war time production, there are a lot of variations. And reproductions are quite common.

Thank you for the additional pictures. It still appears to me the barrel is not flush with the receiver nose. I believe I see a gap. Depending on what you do with this parts kit, you may want to have the barrel removed and then re-installed by someone with the proper tools. What ever you do, just make sure you don't manufacture a machine gun without the proper licenses. There is a lot to learn in the machine gun community. Take your time and become well informed. 

[Countryboy77]

On 8/9/2025 at 10:13 PM, Cbod82 said:

Great info TD! thanks! I mistyped the frame serial earlier, it’s 496 not 406, but maybe still the earliest you’ve seen with the square mag slots? I’m really not one to be overly concerned with hiding non matching serialized parts, so here you are!

Really going to show my ignorance here, but what’s the story with the different style mag slots? I know the M1s can’t accept drum mags due to a design update. Is this what the square mag slot indicates?

Interesting thought about this one potentially having been issued outside of the UK, but like you said, between the mismatched parts and probable wartime replacement parts, it’s pretty hard to establish any sort of real provenance. Despite the thrown together nature of the kit, I’m extremely happy with the overall condition and solid presentation appearance! 

Square mag slots is the shape of the hole the magazine track rides in and roundes or square corners as well as drum rails have different styles too.

[thompsonteenager]

I would keep it as is. Its a very nice display kit

[Cbod82]

On 8/13/2025 at 10:51 PM, TD. said:

You did great with the vertical fore grip. It appears you have a Savage Arms vertical fore grip. These are hard to find and expensive when found. Congratulations. I thought it might be a Savage fore grip but the angle at the rear of the fore grip was a little more than I am used to seeing. Of course, with war time production, there are a lot of variations. And reproductions are quite common.

Thanks TD! That is great news for sure! I’ve managed to get all original replacements for the parts this kit is missing, but I’m having a heck of a time finding an original cross pin for the cutts compensator. Hoping that you and the other folks here might have a lead on 1928a1 comp pin!