Tuning Umarex M1A1 Thompson Repair

ninersix said:

The Bolt on the M1A1 is covered in a telescoping plastic. I took some pictures of the upper and lower and moved the bolt, it does not move a whole lot. I made a short video of it. I think it may be a little more difficult to do. What is your opinion?

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YouTube has a video “WE Thompson M1A1 Disassembly & Cleaning, Lubrication Guide”.
This might be slightly different for Umarex but I suspect they both follow a similar design.
It shows the bolt … a substantial alloy piece … which somewhat resembles the bolt in the MP40. If so, it would be a hollow bolt composed of two halves screwed together. And that means you could pack it with lead BBs or pellets before before screwing the two halves back together. The extra weight slows the cycle time quite a bit

borne2fly said:

YouTube has a video “WE Thompson M1A1 Disassembly & Cleaning, Lubrication Guide”.
This might be slightly different for Umarex but I suspect they both follow a similar design.
It shows the bolt … a substantial alloy piece … which somewhat resembles the bolt in the MP40. If so, it would be a hollow bolt composed of two halves screwed together. And that means you could pack it with lead BBs or pellets before before screwing the two halves back together. The extra weight slows the cycle time quite a bit

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Other than the bolt moving back and forth, the Airsoft M1A1 is not the same as the Umarex Co2 BB gun. I am going to have to take apart, at least partially, the Umarex lower to expose the bolt mechanism (very carefully) and hopefully have access to the spring/bolt mechanism and see what is what. It is after all a C02 BB gun and not a Swiss Watch or nuclear reactor. (Taking pictures as I go.)

ninersix said:

Other than the bolt moving back and forth, the Airsoft M1A1 is not the same as the Umarex Co2 BB gun. I am going to have to take apart, at least partially, the Umarex lower to expose the bolt mechanism (very carefully) and hopefully have access to the spring/bolt mechanism and see what is what. It is after all a C02 BB gun and not a Swiss Watch or nuclear reactor. (Taking pictures as I go.)

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While you’re in there, see if there’s any way to add a recoil buffer. Anything that might soften that bolt slamming against the receiver.

borne2fly said:

While you’re in there, see if there’s any way to add a recoil buffer. Anything that might soften that bolt slamming against the receiver.

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Yes, I thought about that also. The telescoping black plastic tubes got my attention. So I decided to compress the black tubes which exposed the sear in the gun after I removed one screw holding the tap cover, it slid forward after I pulled the trigger. After looking at it I started to think about where id the return spring? It must be in the larger tube. The Large tube is stationary, so I compressed the small tube and got a good look at the bolt release. There is a small round peg, probably just a stop, I was thinking how about a smaller spring in the small black tube as an additional buffer?
I do not know without thinking about it some more. What do you think?

It’s interesting that you slowed the action on the MP40. I hadn’t noticed that mine seemed unusually fast. The M1A1 on the other hand definitely is. When it’s on auto I’d guess it’s firing at around 1700 rpm.

The firing behavior of it is what makes me like the MP40 more.

I’ve got the Umarex M1 carbine too and while I’d give that top marks for realism, it’s not half the shooter of either of the others.

ninersix said:

Yes, I thought about that also. The telescoping black plastic tubes got my attention. So I decided to compress the black tubes which exposed the sear in the gun after I removed one screw holding the tap cover, it slid forward after I pulled the trigger. After looking at it I started to think about where id the return spring? It must be in the larger tube. The Large tube is stationary, so I compressed the small tube and got a good look at the bolt release. There is a small round peg, probably just a stop, I was thinking how about a smaller spring in the small black tube as an additional buffer?
I do not know without thinking about it some more. What do you think?

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I don’t think adding a spring will do it. I’d fish around to find what stops the bolt’s rearward travel and add a soft plastic stop. The bolt spring should push it forward and the Co2 should push it back, but what limits that rearward travel? Now, it’s possible that a heavier bolt might not travel back far enough to hit the frame. That would be ideal … if the Co2 has enough kick to reload but not enough to ram the bolt against the frame.