reconbob

For the longest time I thought the quick way to identify a new manufacture fixed rear M1 sight was to look for the checkering or hatching around the rear sight hole to reduce glare. I saw a sight on GB that looked all original and correct - except no hatching - so I got it to examine. Now, the only source I know of for new manufacture/fake M1 sights are the ones they made to put in the "Russian" M1928A1 kits so they could sell the Lyman 55B sight as an "extra". The "Russian" fixed sight is easily recognized because the fake LYMAN stamp is the wrong size - maybe twice as big as original. The sight I just got is correct in every way, and i would say it is original, but there is no hatching around the sight hole. Here are 4 sights - On the left fake "Russian" sight, next original with no hatching, next original with hatching, and on the right older sight with the full LYMAN address. This sight has the hatching, but it is so faint that you can only see it viewed with a magnifying glass. Here are the apertures. On left, old sight with Middlefield address and barely visible hatching. On the right, original with no hatching On left original sight with hatching. On right "Russian" sight with no hatching. I would say that the presence or absence of the hatching is not the last word. It could have no hatching and be correct. The "giveaway" for the fake sight is the oversized LYMAN stamp. Bob

I have never had a problem with a Richardson receiver, but in my travels I have encountered this problem - usually with aftermarket barrels. The thing to do would be to put the barrel in a lathe and file the thread major with a flat file at low RPMs. This should enable the barrel to turn on a couple more turns. If you get the barrel to screw in 1/2 way I would use fine-to-medium valve grinding compound. Hold the barrel in a padded vise. Put a generous amount on the barrel threads and screw the receiver onto the barrel. When it won't turn any more use a cutoff broom handle or similar piece of wood that will not mar the receiver and use it as a handle to turn on/turn off, turn on/turn off the receiver onto the barrel. You will see that the barrel will turn on a little farther each time. If needed apply more compound to the threads. You should be able to get the barrel to turn all the way on in a few minutes. Once the barrel hits the shoulder of the receiver you're finished. Clean all the compound out of the receiver and off the barrel threads and you are all set. Only 0.001" can be enough extra material either on the barrel or the receiver to make a barrel too tight to screw on. While this may not seem like a precision approach, I have used it dozens of times over the years and it does no harm to the receiver or the barrel. The only "damage" is the bluing will be rubbed off the receiver and barrel threads, but when the barrel is fitted you can't see this and there is no danger of corrosion. Bob

The height of the receiver should be 1.430”. If there is a step and the barrel is the correct 1.00” diameter and the receiver is the correct 1.430” then the next thought is that the hole for the barrel is drilled a little too high. Bob

I never saw this, but if the barrel is original (Savage S or Steven’s square S) with the proof P at top dead center I would figure could be result of wartime production. Measured the diameter of the barrel. It should be 1 inch. Bob

Found in Doug's papers - This is a print of a Ordnance Department B&W photo (Negative #A-692) showing a M1921 barrel with small compensator and corresponding small diameter of barrel where the comp screws on. This is barrel "A" in the photo and is labelled a "standard" barrel. Barrel "B" is what we now know as a M1928 barrel and comp with the larger diameter and longer comp and the large diameter of the barrel where the comp screws on. This is the "proposed" barrel. It's too bad there is no date on this, but it is (I think) interesting. Bob

I had a guy in the shop today that had questions about recoil springs and how to know when it is time to replace them. For some reason he thought that coil springs never show wear. This is incorrect. Coil springs ALWAYS show wear, but with a Thompson recoil spring it is a more subtle thing to recognize. Here is the recoil spring from a Browning Automatic Rifle showing obvious wear by the flattening of the coils of the spring. It's not a great photo but in the middle of the picture you can see the coils are noticeably flattened. Here is a Garand recoil spring - same situation - the flattened coils are obvious - Not so easy with a Thompson but it still happens. Here is a new recoil spring - And here is one with the flattening of the coils, but not as obvious as BAR/Garand because on the Thompson the diameter of the wire is a little smaller. But it's there - the easy way to recognize it is to compare the flat coils in the middle to the round coils in the corners of the photo. So yes, coil springs always show wear and eventually wear out. The best/easiest way to check a Thompson recoil spring is to measure it. It should be 11 5/16" +/- 5/16" long. Bob

If the frame was spray painted that would fill up the pits and smooth it out and sandblasting would blow off the paint and expose the pitting instantly. Bob

If you sloowly pull the trigger when the sear finally trips it drags on the bottom of the bolt slowing it down and causing the jams. Your description of being able to fire long bursts but have the gun jam when you slowly pull the trigger is the exact example of this. I have had this conversation dozens of times over the years, mostly with guys that have rental ranges. Rookies come in and pull the trigger very slowly as if the Thompson is a target rifle….and the gun jams. The way to shoot a Thompson is to fully and decisively pull the trigger then let it go. If you want to fire single shots use the selector. If you found a bolt that works even with the “target” trigger pull I would figure the bolt is worn in some way. My $0.02 Bob

I do not have the detalls in front of me but if I recall various areas of the M1/M1A1 bolt body are hardened to RC 62-70. That is too hard to machine, even with carbide. You can't file a Thompson bolt - the flie skids right off like it's glass. You could probably anneal it, but I do not know how you would do that. Bob

The easiest thing to do here would be to machine the M1928A1 pocket, cut the wings off the bronze lock, and use the gun that way. Trying to use an M1 bolt would (in my opinion) be more trouble than it is worth because it is too hard to machine (for a top cocking handle hole), but mostly because on the M1 the buffer pilot and recoil spring are on the center line of the bore. On the M1928A1 the buffer pilot and recoil spring are 0.100" BELOW the centerline of the bore. So unless your receiver has not been drilled for the buffer pilot yet, the bolts are not interchangeable. One problem with the angle cuts for the bronze lock is that you can't measure/check it until after you machine it, and if you get it wrong you can't fix it. Bob

Ok. Did not realize they were that old. I stand corrected! Bon

On a separate and now deleted thread there was a discussion about the origin of ball knob style cocking handles. Kahr/Auto-Ordnance made them. Here is a knob/handle from an American Historical Foundation Vietnam War semi auto Thompson commemorative. These were made by Kahr I would think by now at least 30 years ago, maybe longer. Bob

Bob

I am away from the shop, but I brought some actuator drawings with me. One is a copy of the original Colt drawing of the M1921 actuator. On this drawing for whatever reason the location and width of the knurl is called out, but the diamond pattern is not. The width of the knurl is 0.30” +/- 0.01” and is centered on the ball which is 0.680” diameter. From Doug Richardson’s drawing of the M1921 actuator he specifies the knurl as 32 TPI, 45 degree LH/RH concave pattern knurl. The actuators Doug made were perfect except he either could not get, or did not want to pay for the correct 32 TPI knurls. He used 36 TPI. Knowing Doug 32 TPI must not be available because he was a fanatic about details. The 36TPI must be a standard because it is available off the shelf, but as noted last I checked was $850 a set. i wonder about the 90 degree knurl. If I understand correctly, that would not create a diamond knurl, but a box. Bob

From looking at the photos the bolt face appears damaged and or corroded so the bolt has no value. There are still tons of MINT bolts out there. A used bronze lock might be $35. The actuator is the good part. If you are making a point not to gouge anyone you can sell it for $100. You can also sell it for $200-$300. You criticize Gunbroker, but GB is a valuable resource for monitoring prices. Nobody is forced to bid on, or buy anything on GB, so I don’t see where the gouging takes place. If people think it’s too expensive they don’t bid or buy. Some Thompson parts have been up on GB for years (am180 Colt rear sight, 1921Industries sear, etc.) and not sold because of condition and price. You wonder why people bother, but it’s a free country. Bob