Replacing Mag Catch Spring On Ao 1927a1

[Milwroad]

Relatively new to Thompson's, but I have one that obviously has a spring issue with the mag catch. The mag catch just flops around back and forth and won't hold a stick mag in place. I assume I need a new spring. Question is, how do I replace it? Do I need to disassemble the AO 1927A1 receiver to seperate the top and bottom groups? Do I need to remove the safety first? Any help appreciated. Thanks

[roertmcw]

Careful or you will scratch the lower receiver when you remove the Pivot Plate. I understand you can get special tools do it so you won’t mess it up. I hear if you are good enough with you hands, you can use a business card. When you do it, you should fix the mag catch so you can use GI mags.

 

Robert

Edited August 24, 2011 by roertmcw

[darrylta]

You more than likely broke one of the spring tangs off. Use a GI spring when you replace it.

 

You will not have to remove any thing else before you remove the mag catch, just push on the mag catch pin on the

right side of the frame with the butt of a hammer, while raising the mag catch lever. This should give you

enough room to wiggle it out of the frame.Normally, this procedure can be done without finish damage.

 

Pivot plate & ejector work are the tasks that require patience and task specific tools.

 

-Darryl

Edited August 24, 2011 by darrylta

[roertmcw]

From http://www.1927a1.com/

 

 

1927 Semi-Auto Magazine Catch Modification

 

 

The semi automatic Thompsons will not accept original G.I. 20 and 30 round stick magazines.

The magazine catch must be modified by lowering the lip that engages the magazine .100" while maintaining the original contours and shape.

This is commonly achieved with a Dremel tool or files.

 

Make certain that the firearm is unloaded, place the safety in the fire position and squeeze the trigger.

Using a dowel or other object that will not mar the finish of the frame push up on the pivot plate finger that holds the safety leaver, push the safety out.

After you have removed the safety, move the pivot plate so the ends of the pins are flush with the side of the trigger frame.

Pivot the magazine catch out far enough to clear the magazine engaging protrusion from the hole in the trigger guard.

Push on the pin part of the mag catch on the far side while pulling the catch out of the hole.

Once the magazine engaging protrusion has cleared the side of the trigger guard, carefully allow the catch to rotate and unwind the spring.

Remove the catch from the trigger housing . (Assemble in reverse.)

 

When re shaping the magazine catch, you must duplicate all the contours and angles when lowering the engaging surface.

Removing .100" will allow use of unmodified GI magazines.

Be careful not to remove too much metal.

You may have to re fit and test several times to achieve the optimal shape.

 

 

[Milwroad]

So the post right above this suggests I have to remove the safety while the one above that says I do not. Which is correct? ThanksThanks

 

 

 

Edited August 25, 2011 by Milwroad

[darrylta]

Milrod,

It's been several years since I did this mod on a semi. I don't remember if I pulled the pivot plate pins flush with frame or not.

It'll be easy to check and see if you need to by rotating the catch to see if it will clear the safety and pin. If it doesn't you'll have

to pull the pivot plate till the pins are flush.

The pivot plate fingers should not be as stiff as a GI or Colt plate, so maybe a pivot plate tool will not be needed.

If you need a pivot plate tool, PK and D. Richardson both offer these tools at a reasonable price.

 

Maybe someone else can chime in with more concise instructions.

-Darryl

Edited August 25, 2011 by darrylta

[dgrasshopper]

Relatively new to Thompson's, but I have one that obviously has a spring issue with the mag catch. The mag catch just flops around back and forth and won't hold a stick mag in place. I assume I need a new spring. Question is, how do I replace it? Do I need to disassemble the AO 1927A1 receiver to seperate the top and bottom groups? Do I need to remove the safety first? Any help appreciated. Thanks

Iam new to the Thompson too.

I bought a cd on the Thompson from AGI at www.americangunsmith.com 1-800-797-0867 that covered the disassembly asssembly of models 1921,1928,M1 and 1927A1. The members of the forum have helped me with my 1927A1 .I found this CD very helpful.

It is great to actually see how to do it, however the armorer is aliitle rough with the screw drivers etc. on the finish.

 

[TD.]

Welcome to the Board!

 

I don't own a semi-automatic Thompson. However, I am pretty sure you will need to remove the frame from the receiver before doing anything else. The frame is the part that contains the magazine catch. This is an easy job with a full-auto, not so with a semi-automatic. I have heard you need a long thin screw driver to depress the frame latch button when the frame is about 1/2 way off the receiver to finish removing the frame from the receiver. Perhaps someone with some actual knowledge of the semi guns can join in.

 

I would assume you will have to remove the pivot plate to replace magazine catch spring. I do know if you remove the pivot plate from the frame with the receiver attached to the frame you will have a big problem that will most likely require an expensive trip to a gunsmith. I would also guess you will need to at least partially disassembly the frame after removing the pivot plate to then remove the magazine catch so you can replace the magazine catch spring. I used a large bladed screw driver with the blade wrapped in duck tape for several years without any problems before buying the specialized tool mention above. This will allow you to move the arm of the pivot plate to then remove the safety lever.

 

None of this is very hard the second time one does it. However, it can be a mess if you don't have some pictures to guide you. Again, someone with some specific knowledge may be able to point you to a manual or book with pictures that shows how this is done.

 

The magazine catch modification mentioned above is a good one. However, first get your Thompson in working order. Buy two of the magazine catch springs so you will have a spare.

 

Good luck!

[TD.]

There is a copy of an AOC Kahr Semi-Automatic Thompson manual at this site that will help you remove the frame from the receiver:

 

http://biggerhammer.net/manuals/

 

 

 

[OldFalGuy]

DO GET a pivot plate tool- or a real hard stiff plastic- I like the wood tools