PhilOhio

Wow, that didn't take long. Nice looking kit, fair price, away it goes. Wish all the gun shows worked that way.

Exactly what gun was this, Ron?

Well, I've greased more than a dozen of them, without grease coming out the back, except for almost enough to lubricate the camming surfaces of the ratchet part. Either way gets grease to the spring, but it is far simpler with the Harbor Freight clamp.

Put another way, what Jim is trying to say is that the cyclic rate refers to how many rounds per second the gun fires while you are pulling the trigger and it still has ammo.

Good for you, Gutterratt, but why go to all the trouble of removing the rotor to grease it? Just drop by any Harbor Freight and buy their wide reach C-clamp, stock #45916. Then you only remove the drum cover. Easier is better. Sounds like a fair price. Nice work.

Bob, As for advanced primer ignition and whether it relates to these slam loaders with stud firing pins, all of them must have a protruding lower lip on the (thus recessed) boltface. And all of them have a fairly stiff extractor spring. The extractors all have angled faces, which must cam completely up and over the cartridge rim and snap back down BEFORE the stud firing pin can possibly touch the primer. This is how the M1A1 Thompson works. Because of the strength of the extractor spring, it cannot snap over the case rim until the round is fully seated...completely stopped against the front shoulder of the chamber. Then bolt inertia is dissipated by, in order, (1) the extractor snapping over the rim, (2) the pin denting the primer, and (3) the cartridge base seating against the recess in the bolt face. This sequence is why I can't see that advanced primer ignition could take place with this type of firearm. It seems to me that it is a physical impossibility, except... ...if dirt, unburned powder grains, or brass shavings create an interference fit, so the round is aligned with the bore but cannot go all the way in. Then there is enough resistance so that the extractor can snap over the rim and the pin can fire the primer prematurely. We have out-of-battery firing, with the case either being severely bulged or exploding...and I've experienced it with a stuck semi firing pin. If by chance the case is seated far enough, but not all the way, the strong part of the case, the web, should still hold the pressure. I've recovered incredibly bulged 7.62 x 39 cases from a range where the web held full pressure, when some idiots were apprently trying to make some Sov Bloc rifle go full auto with some jerry rigged setup. My buddies and I keep a couple of these as souvenir reminders to urge young guys on what not to try. Am I overlooking some technical factor here? Now, I know that many things can be done to increase rate of fire, and I'm wondering if some designers have, in the past, incorporated some of them to boost ROF and have, mistakenly, attributed part of their success to advanced primer ignition? I have also seen the term used in a context which suggests that the author mistakenly thought all slam loaders work on the principle of advanced primer ignition, because he doesn't understand how it really works on something like an early MG-42. In that case, just as the roller locks are about to go into their recesses the striker is allowed to contact and fire the primer and powder burn begins. So, hopefully, by the time pressure builds up, the bolt will be locked. If not, you have big fireworks and brass fragments coming out of the ejection port. Often it did. So the Germans admitted to a rare "oopsy" and gave up on advanced primer ignition MG-42s. So far. As for info on this phenomenon vis a vis MG-42s, there's a wealth of technical and historical information and documentation widely available, and it's really fascinating. Fortunately, the Germans documented everything to death, so all the knowledge they gained was not lost. You can still buy both kinds of MG-42 bolts, the old and scary kind, and the later safer and slower one, as used on current versions. I think some members here have 42s and know a ton more about this than I do. Wish I had one of those babies; got an H&K Lafette mount and optics just waiting for it...perhaps waiting forever.

Ron, All the post-war semis work about the same, because it was so much trouble coming up with a design which would satisfy ATF that nobody wanted to go through that again, until recently. Tim Polston has a newly approved design which will be more like the "real" Thompsons, uses more of their modified parts, and will be rather expensive, I suspect. Sounds like it would be The one to have. You might want to research those threads on this site and take a look at http://www.thompsonsmg.com/SEMI_AUTO_INFORMATION.htm All of the semis marketed so far fire from a closed bolt and use a spring-loaded striker firing pin. You can also fit an original full auto lower assembly to them, which will still not let them fire full auto. There is no Blish lock in any of these. They are all unlocked, depending upon the weight of the bolt and high pressure metal adhesion to keep the breech closed until it can safely open. The spring which drives the bolt and helps hold it forward during firing is also MUCH stronger than the spring on a full auto Thompson. This whole system works just fine and is quite safe. This is a long and complicated subject, but in a nutshell, that's it. The Polston design is very different and I am not familiar with all its details. You still need to get the nomenclature untangled a little bit more. It takes awhile to remember all this trivia. The full auto versions, in historical order, were 1921A, 1921AC, 1928A1 and 1928AC, M1, and M1A1. There are a couple semantical variations within those, such as the "Navy" and the 1927 semi. There was no 1928M1. All the postwar guns were semis, except for a few full autos which George Numrich put together during the '60s from surplus parts and a few which he made. All of them up through the 1928 series were much the same. The M1 was a major wartime redesign, as was the M1A1 which followed closely. That was the last of the classic full auto Thompsons. All the semis which followed may look like Thompsons, but they are very different internally and the dimensions were required, by ATF, to be quite different. Sadly, what differed most of all was the often poor quality of the semis. Those from Kahr Arms, most will agree, have so far been the very worst. Just when we think it is improving, our optimism usually turns out to be premature. So when buying one, especially a new one, you have a more daunting task than if you were buying a full auto gun which passed through a rigid military acceptance screening procedure decades ago. David, Another question which occurs to me...by any chance, do you know if the .45 Remington-Thompson ball cartridge would fit the special magazine made for the shot cartridge? That might be where the shot mag originated, and it could have dictated the overall length of the shot round, as a matter of convenience. As I recall, the 1923 Thompson was very different from the series which started with the 1921, and existed as what were basically prototypes. Doesn't Allan Cors or Tracie have one of those? I know I've seen one someplace.

Ah, the dopey things we did when young, because we didn't know any better. When I bought my '28AC in '69, I could have had an original case (purple lining) with all the accessories in it, for next to nothing. I thought it was clunky, useless, and who would want one of those? So all I took out of it was the original minty numbered Colt "L" drum, at no extra cost. Why would anybody want the silly tin Altoids box, except to carry around spare suppositories or candy? And there was a brass cleaning rod and a few stick mags. I took a couple of the mags, fortunately. Turned out one was a UD-42 9mm, which I now use with my quick change barrel. But the case...wonder where it went? Maybe a dumpster in Wheaton, MD. I thought since I was already spending more on the Thompson than any gun I had ever bought ($387), I'd better control myself and not spend a few more bucks on something I "needed" even less. I think about that case too often.

Now, THAT scares the bejeebers out of me, and should be the kind of thing that makes us all take this issue seriously. Who knows how often that happens? Or whether it is very rare, but will happen at the next show where you get casual with your guns? I not only don't want to lose mine, but I feel an obligation to not make it easy for them to fall into the hands of somebody who may do something terrible with them. I'd never forgive myself...nor the slob who left the doors unlocked.

David, When you mentioned the ".45 Remington-Thompson cartridge", were you referring to a ball round with almost the same name as the shot cartridge? If so, guess I've forgotten that one. Ron, When David mentioned that it was discovered that the Blish bronze lock was not necessary, it was because of emerging appreciation for the fact that several other factors did a "good enough" job of keeping the action from opening too soon after firing. First, the weight of a heavy forward moving bolt generates enough inertia to delay ejection slightly. Second, during the high pressure phase of the ignition cycle, the walls of the cartridge case expand to seal the chamber and also adhere with great force. We're talking about thousands of pounds per square inch. This is more than enough to seal the breech and prevent ejection until long after the bullet has left the muzzle. Pressure then rapidly drops almost to zero, but just before that, residual low pressure helps to eject and drive the bolt rearward, along with rearward energy now equal to the kinetic energy of the moving bullet. Pretty interesting physics.

Bob, Very good and interesting post, but whenever the subject of "advanced primer ignition" is raised, so are my eyebrows. For the most part, I don't believe it exists in many of the firearms where it is claimed to exist, primarily slam loaders. There can be such a thing, but only where it is carefully and intentionally designed into the mechanism, and in a gun of a different type. The Thompson is not such a gun. I've heard it used to explain high ROF in Suomis of the WW-II era, for example. Nope. Also wrong type of gun. But even the Finns believed they were doing it. In WW-II, the Germans made the MG-42 an advanced primer ignition gun; turned out to be a very bad and dangerous idea. They back tracked, slowed things down, and turned it into a safe and reliable gun again, albeit still very fast. You simply have to allow for the possibility of unburned powder grains and dirt, partially obstructing the chamber walls, turning your cartridge into a mini grenade. When firing hundreds or thousands of rounds in a very short time, the odds grow against you very fast. Everything depends upon whether the bolt (and only a bolt with a stud firing pin and recessed bolt face) has an extractor with reasonably strong and adequate spring loading. If it does, there is no way in the world that the firing pin can dent the primer until the live round is fully seated in the chamber, with its case mouth solidly stopped by the forward end of the chamber. Only then can the extractor snap over the case rim, and only after that can the pin dent the primer. And that is not advanced primer ignition. Now, if you have a Thompson M1A1 with a very weak extractor (snaps over the rim way early), or if you have dirt and debris creating a tight chamber situation, you sure can get advanced primer ignition...REALLY advanced...out-of-battery-firing advanced. So with an M1A1, the way I understand the mechanism to work, the primer begins to be dented only when the case is fully and firmly seated, with extractor snapping over the rim, but when the bolt still has, let's say, 1/64th" to 1/32" more to go. This distance represents the depth to which the primer will be deeply dented. And that means the bolt still has most of its inertia stored, probably helping to delay ejection slightly. In any event, pretty interesting stuff. To you and me, at least. So my understanding is that, unless you have an extractor designed to not quite work (right), you can have only slam loaders that fire in-battery. Fully so. But you can design a moveable firing pin gun (not a slam loader) to trip the sear just before the action is closed and locked...if you like to live dangerously...or let somebody else do so. The Germans had a lot of soldiers lose their eyesight that way. First, they gave them goggles to wear. I imagine you could spot the MG-42 shooters by their brass fragment pocked faces. Then they started taking smart pills, and scrapped the advanced primer ignition concept. Maybe somebody is doing it again these days. I don't know. But I don't want to shoot one of those.

Bnew, I'm wondering what Thompson you have, which you expect to fit into the case. You say you are redoing "a 1927". Do you mean a 1927A1 post-war semiautomatic Thompson with a 16" barrel, which would certainly not fit? Or such a gun with a shortened barrel, registered with ATF? Or one of the rare 1927 original Thompsons, which is really a gun with the full auto receiver and short barrel, which would fit? I hope you are not shortening the barrel of a post-war semiautomatic Thompson, to make it fit, without realizing that a few formalities are required first. As for the tightly fitting strap, I hope you are treating it with something to preserve it and make it flexible, to avoid breaking that very old leather. Sounds like you have a real treasure.

Ron, You are getting a lot of really good, detailed advice from all of the people who have posted above. The best advice is to study those reference books, a lot. It has taken all of us years to absorb just some of it. And there's alway more. But it won't take as long to understand enough to make a fairly good purchasing decision. The only advice I would add is to back track a little, and reconsider whether you would really prefer to own a semi or a full auto Thompson. In quality, there is no comparison. Most full autos are totally superior to any semi ever made. You would never be unhappy with a full auto Thompson, and your investment is more secure, but it doesn't often work the other way around. Cost is high, but it is possible to get a full auto WH Thompson (made post-war in West Hurley, N.Y.) in the $12,000 range, I believe, especially in these softening market times. And the price may go lower. If you have the ability to sell some other guns to fatten your Thompson budget, it is worth seriously considering. Looking back, you will never be sorry. The critical factor is whether you live in a state where all this is possible. If you do, you should not let distance of the nearest Class III dealer license holder slow you down in any way. All of this is small stuff. If you really get into the appreciation of Thompsons, you may wish you had bitten the bullet at the outset, as you come to realize that the cost of buying a semi would be a significant part of the cost of a full auto gun. But if you are pretty sure that a semi will make you happy, and simply don't want to have a lot of money tied up in a full auto gun, then go for the semi, and make the additional investments necessary to get it to run right and be a treasured possession. Some members here have created real show pieces, with the help of specialists referenced in the FAQs section.

I've thought about this issue a lot, over the last few years. I have never brought it up, because it seems like a potential hot potato. But denial is probably not a good thing. I am hesitant to suggest that it might be very wise to raise this question with somebody responsible at ATF Headquarters...somebody in a cooperative and supportive frame of mind...but I think it may be overdue. Any thoughts, T-man? I know that our position is that we all try hard to follow the rules and have a lot to lose. Just one theft of a privately owned automatic weapon from a hotel or motel room, followed by the criminal use of that weapon in a major incident or mass murder, could spell the end for private ownership of this type of firearm in the United States. Just think about that for a moment. It is not an alarmist daydream. Anything like that would be vigorously seized by the present leftist regime, as an excuse to ban and confiscate all private automatic weapons on an emergency basis, and use this as the kickoff for much broader legislation already in draft. Frankly, I don't know what the right answer is. I'd like to know. What do we do with our Thompsons when away from home, while in a restaurant, while shopping or socializing in a night spot? We read more than one report each year where one, or more than one, automatic weapon is stolen from a police cruiser or the private vehicles of off-duty policemen who did not store them securely. The officers usually get away with it, with little repercussion. We would undoubtedly be held to a different standard, not yet established. This worries me a lot. And it should worry you. The negligence of just one Thompson owner could change life for all of us. And it would not really have to be genuine negligence. Reasonable behavior may easily be twisted into a propaganda assault. Please, give this some serious thought and share those with us.

Those aftermarket buffers are also spacers. Decreased bolt travel = increased ROF. As long as you use a reasonably pliable buffer, to moderate bolt impact shock, and as long as you don't use loads that are really dangerously hot, you are not likely to crack the receiver of any well designed, mass produced firearm. Take a look at the extremely long rubber buffer/spacer which IMI used in the original Uzi Model "A", like I have; several inches, as I recall. It allows much shorter bolt travel than the buffers in the above url. It would be interesting to measure the very high ROF this would probably produce if installed in a full auto Uzi.