New Thompson 1927 A1

[alanint]

Both the Sten and MP40 have a much longer bolt travel than the UZI. The UZI's telescoping bolt allows for shorter travel, making it the least "clunky" of the three to fire. All three of these guns also rely on advanced primer ignition to somewhat mitigate the slamming home of their bolts. The Thompson relies on the shear weight of the bolt to fire the cartridge and has the least bolt travel of the lot. In the 1921 and 1928, the Blish Lock provided friction slowing of the bolt. The M1 and M1A1 eliminated the Blish Lock, but had a heavier bolt to make up for the Blish's slowing action on the bolt.

[ithacaartist]

Let's see if I understand...
The semi-auto's bolt is in place, closed and locking the breech, when the trigger is pulled to release the firing pin, which ignites the primer, firing the round--which sends the block and fp back together. The firing pin is engaged by the sear and retained until the trigger is pulled again; the block is pushed forward, back into battery by the recoil springs, picking up and chambering the next round from the mag.
I'm trying to visualize the sequence for full auto, and what you've described reminds me of a slam-fire, but controlled. How do the firing pin and block relate to each other mechanically in the full auto? Are they locked together somehow on the way forward?
Don't full autos also have a third position of the safety switch for full auto? (I'm figuring that the switch would cause the action to bypass the disconnect, and keep on cycling and firing as long as the trigger is held.)

[rhuff]

I am pretty sure that your semi-auto Thompson is a pure blow-back action, as was the original Thompson, and not a locked breach action. The Thompson M1, and M1A had a fixed firing pin in the breachface, and when the bolt reached battery, or slightly before battery, the primer was ignited, and the whole process started over. The selector switch changed the sear engagement between the semi and full auto mode on the 1921, 1925, and 1928 models. I don't own an M1, or M1A, so am not really sure exactly how the selector switch functions, but likely very similar.

[ithacaartist]

I guess I meant "closed" as opposed to "locked", sorry. I can understand how it would not be "locked" for a blow-back action. The P.08 breech is locked for the first 1/4", until the toggles are deflected upward to unlock the toggle joint, right?
Yup, as I suspected, the integral, or fixed, firing pin makes sense as it uses the momentum of the entire block to ensure ignition of the primer. My next question is, how does a fixed firing pin work in semi-auto position of the selector? Outwardly, it would appear the f.p. would have to be "un-fixed" somehow for semi-auto. (I need a Gerard Henrotin e-book for this!)

Update on warranty situation: I called customer service and got an RA# so I can send it in for fixin'.

[alanint]

Correct, with a couple of clarifications. The semi is a blowback action. But the 1921 and 1928 where a DELAYED blowback action through the friction created by the Blish Lock. The bolts on the 1921 and 1928 are essentially two pieces, where the Blish actually mates the bolt to the actuating knob on the top of the gun. One could even argue that these two guns were of LOCKED breech, since the Blish Lock did have two ears which mated with channels in the receiver when the bolt drove home and were released when the bolt flew back. Something akin to a rudimentary roller lock setup like the MG34, MG42 and the HK series of weapons.

The M1 had a firing pin, spring and hammer, just like the 1921 and 28, but the bolt was simplified, made one piece and was actuated by a handle directly mated to the bolt and on the right side of the receiver, instead of the top. The bolt of the M1A1 was longer than the M1's and the firing pin on the M1A1 was machined directly into the bolt face and the independent firing pin, spring and hammer of the M1 were eliminated. In fact, this is the only feature which distinguishes an M1 from an M1A1.
The M1 bolt stopped when a channel in the bolt reached a battery position, allowing the hammer to drive home and hit the firing pin. The M1A1 bolt stopped when it could go no further than the cartridge base would allow. The M1A1 was slightly more suseptible to dirt and debris because of this, but had fewer parts to worry about than the M1. Both guns operated via a sear trip in the lower receiver, which would allow the bolt to keep going or to stop after each shot, depending on the position of the selector. Both full and semi auto fired from an open bolt.

[alanint]

My next question is, how does a fixed firing pin work in semi-auto position of the selector? Outwardly, it would appear the f.p. would have to be "un-fixed" somehow for semi-auto. (I need a Gerard Henrotin e-book for this!)

David, the action works in either semi and full because they both fire from an open bolt.

[rhuff]

I have learned something today, as I, obviously, thought that the M1, and M1A1 both had fixed firing pins in the breachface. I have never spent any time with either one....the 1928, well about 40 years. There are a lot of differing opinions concerning the Blish Lock system, and exactly how well it did or did not work. It makes for interesting reading.

The M1 and M1A1 Thompsons were much simpler and faster to manufacture and therefore cheaper to purchase than the 1928A1. They will only utilize the box mags, not drums, and had very simple sights over the Lyman adj. rear sights. Also the Cutts Compensator was dropped. It looks like a 1928 somewhat, but is quite different in many ways.

[alanint]

The Blish Lock did perform a function in slowing the action down a bit, but was really unecessary for the safe or reliable operation of the TSMG. One realizes how much the Blish does influence functioning when you try to Blank a 21 or 28. They will simply not run with a Blish as designed installed. You have to lop off both the "ears", which ride in the channels completely off the Blish Lock, keeping the central "H" piece intact for it to mate the bolt and actuating assembly in order for a 21 or 28 to run with Blanks.

[masaes727]

The rattle your getting could be coming from the stick mag not seeding well. I had the same gun not that long ago, with the same issues. The hole in the back of the mag where it literally locks into the gun is not in the exact spot it should be. Its about an 1/8 to a 1/16 off (to high). To remedy this I slighty elongated the hole at the bottom with a dremel tool. This made the hole sorta look like an egg. But, solved the problem, no more rattle. The drum mag, I never really did figure out. Mine would not feed well at all and getting in/out of the gun was an adventure in and off its self. YouTube helped figure some of it out.

[alanint]

Actually, ALL TSMG mags supplied by first Auto-Ordnance of West Hurley and now Kahr use a proprietary magazine release, which is elongated, thus not allowing the use of GI mags. The mags they supplied had an elongated hole to interface with the elongated mag release they provided.
Please don't ruin a bunch of GI mags by elongating the holes. Rather, round off either the top part or bottom of your magazine release so it is round, not oval. This way, any GI mags you pick up will fit the gun. First look carefully at the mag/release interface, so you can see where material needs to be shaved off the magazine release. Take off a little at a time until an unmodified, round hole GI mag pops in snug.

Good Luck

[CAP Black]

sounds quite clever to me.
Jack

[ithacaartist]

Originally Posted by masaes727

The rattle your getting could be coming from the stick mag not seeding well. I had the same gun not that long ago, with the same issues. The hole in the back of the mag where it literally locks into the gun is not in the exact spot it should be. Its about an 1/8 to a 1/16 off (to high). To remedy this I slighty elongated the hole at the bottom with a dremel tool. This made the hole sorta look like an egg. But, solved the problem, no more rattle. The drum mag, I never really did figure out. Mine would not feed well at all and getting in/out of the gun was an adventure in and off its self. YouTube helped figure some of it out.

The rattle is between the upper and lower when assembled, so the mag isn't involved.

I was made aware of the mag release issue even before I bought the gun. The 30 round pre-NY ban stick fits and feeds OK. My problem with the drum mag is that it won't move into position without binding up really tight about halfway in.

Fear not, the rifle and drum mag left via FedEx yesterday, headed to the factory in Worcester, Mass to have my laundry list of issues attended to. It could have left Friday, the day the pickup was originally scheduled from the other end, but since I was basically ill-informed of this, no one was here to see it off, even if it had been packed and ready to send--which it was not.

[alanint]

Although I would never add this to a "how too" manual, I have solved fit issues with West Hurley and Kahr made drums by taking the "ribs" built onto the side of the drum, (which are meant to slide into the grooves in the gun's receiver) and pressed them flatter in a vice. If you compare a Kahr or West Hurley drum to an original Colt or Seymour offering, you will see that these ribs are really poorly formed on the later drums. They are thicker and rounder and not a crisp fold as the originals are. Colt and Seymour show a very neatly folded and pressed rib, which is uniform and flat across its length. The WH and Kahr drums show a weakly rounded pressing, which is invariably thicker than the groove channel in the gun's receiver. Many people make the mistake of grinding on the gun's channels to achieve a fit. By taking the drum's pressed ribs and laying them flat into a crisp edged vice, you can squeeze this poorly rounded rib into a flatter, thinner profile, which should then fit the gun with minor filing and fitting. I would rather screw up a $100 drum than the gun's receiver.

[rhuff]

Agree 100% with the above. When doing an alteration/modify to a part, in most situations, I do the modification to the cheapest, and most readily available part. It has saved my butt more than once.

[ithacaartist]

Doug and Richard, I agree completely. My observations led me to the same conclusion about the fit--the pressed rails of the mag are indeed too crudely formed, and the squeeze in the vise would have been the first thing I'd have tried. However, my thoughts were that two new items that are supposed to fit together, both made by the same place, should fit together right out of the box; so the drum mag went right back to them along with the rifle so they can make good on what they've sold me.

Modifying the cheapest, most available part is the way to go, and usually the modification of the gun is my last choice. The most recent exception I've perpetrated, contrary to this rule of thumb, was to file out the mag well of my Erma KGP69, which refused to accept two spare mags, and the original didn't slide in very well, either. About 2/3 of the way in, there was a "step: in the sides of the well, an offset created by a slight misalignment of the molds used for casting the frame. The only other way to insert a mag fully would have been to pound it in with a hammer!

By the way, an Auto Ordnance 10 round drum mag's MSRP is closer to $190! (I found a discounted unit for $150 with free shipping) Want a 100 round drum? Prepare to cough up over $600! Interestingly, unless the spring for the drums is different, the only difference between the two is the shortened 10-round segment of the guide spiral retained to present this functional capacity. I'm wondering how it is justified to charge that much extra for what amounts to about $1 worth of sheet metal and few extra minutes of fitting/assembly time to install it to allow for the full capacity of 100 rounds.

[rhuff]

Originally Posted by ithacaartist

Modifying the cheapest, most available part is the way to go, and usually the modification of the gun is my last choice. The most recent exception I've perpetrated, contrary to this rule of thumb, was to file out the mag well of my Erma KGP69, which refused to accept two spare mags, and the original didn't slide in very well, either. About 2/3 of the way in, there was a "step: in the sides of the well, an offset created by a slight misalignment of the molds used for casting the frame. The only other way to insert a mag fully would have been to pound it in with a hammer!

I know what you are talking about with modifying a mag well. I have this very inexpensive(read cheap) Spanish Echasa Eibar 380 auto(MAB copy) that had way too tight of a mag well. There really was little that I could do to the mags without destroying them, so I worked on the alum mag well. I finally got things releived enough for the mags to enter and leave with minimal drag(from the mag catch). I don't believe that I would have done that to a Luger, but most likely would not have need to do so. Some of these very inexpensive imported handguns from the 1960s and 70s, really were Saturday Night Specials.

[ithacaartist]

Originally Posted by rhuff

I don't believe that I would have done that to a Luger, but most likely would not have need to do so. Some of these very inexpensive imported handguns from the 1960s and 70s, really were Saturday Night Specials.

++1!

Good point. the Ermas originally sold for less than a hundred bucks. The use of cast Zamak frames (and uppers, in some cases) resulted in savings in machining costs, it obviously also opened the door for some mistakes in castings to elude QC. Luckily, it was fixable in our cases (was your .380 cast or billet?),but a good lesson to seek true quality craftsmanship.

[rhuff]

Cast alum frame.

[ithacaartist]

Originally Posted by rhuff

Cast alum frame.

Was the material you removed presenting a similar situation--the "step" from misaligned mold elements, or was it just too small inside, overall?

[rhuff]

Just too small/tight in one particular area. Once I "hogged it out", the mags went in and out in an acceptable manner. I did not expect them to be drop free, as this pistol was made before that was popular.

This handgun is a Spanish Echasa copy of a French MAB(they used the same parts) which was a sort of copy of a Walther PP/K, but only single action....if all of that makes any sense to you.