SEMI-AUTO INFORMATION
Shown below is the 2S, MS drawing. It can also be used for the 2MM & M2 bolt cavities and the back end of the 2M2 receiver.
SEMI-AUTO RECEIVERS
For those who want to build a semi-auto gun, I offer my 2S and MS
(“Shop™”) receivers which rely on the Numrich/Kahr (N/K) gun design
approval. (There is no approved design that allows a TSMG receiver to be
made into a semi-auto.) These receivers are 1/10” less high than a TSMG
receiver and are interchangeable with the corresponding N/K 1928 and M1
style semi-auto receivers except that the firing pin clearance groove in
the top of the N/K trigger housing must be extended rearward. This is
because my 2S and MS receivers are meant to have a bolt cavity that
extends all the way to the back of the receiver like a TSMG. This has
nothing to do with the gun being semi-auto or full auto. This is done in
order to use the extra bolt travel to absorb the recoil rather than
depend on ultra stiff recoil springs to do it. This requires the recoil
springs holes in the bolt to be deepened to enable the use of longer
pilots which are necessary to retain the recoil springs. These receivers
require a modified N/K Bolt, modified N/K Firing Pin, special Recoil
Springs (2), special Recoil Springs Pilots & Plate, special Firing Pin
Spring, standard M1 TSMG Pilot or my M1 TSMG Sling Pilot (used in place
of the 27A1 Firing Pin Spring Pilot), special Hammer and my 2S or MS
bolt handle. The 2S and MS receivers also differ from their N/K
counterparts in that they are made from the same heat treated steel
alloy used in my TSMG receivers, the rear sight is properly positioned
and the quality is much better.
If it is desired to fit a Thompson SMG barrel (10-1/2” long) to the
semi-auto and not register the gun as a “short barreled rifle”, it is
possible to make a pistol by using a horizontal forearm and a trigger
housing that has no provision for a buttstock if the receiver can not
accept a standard trigger housing. For that application, I offer trigger
housing rails on the receiver that are wider than normal so that a
standard trigger housing can not fit onto the receiver. A standard N/K
trigger housing can be used by deepening the receiver rail slots.
Bottom view of 2S receiver assembly showing internal parts fitted to an extended bolt travel receiver.
MS receiver assembly would appear the same.
My original version extended bolt travel receiver, which I call the 2S-1, used a drop-in 1928- style bolt handle in the standard N/K bolt handle hole. This required the bolt handle hole in the receiver to be placed farther rearward than it is on a 1928 TSMG. The parts illustration for that version is shown below:
To create a more authentic 1928 style gun, a new 1928-style bolt handle was designed to be mounted farther forward on the 27A1 bolt than is normal for the 27A1 gun. The new bolt handle combined with a bolt handle slot on the top of the receiver that is identical to a 1928 TSMG, creates a receiver assembly that virtually duplicates the appearance of a 1928 TSMG. I call this version the 2S-2. It is the one I am currently offering in my catalog. The parts illustration for that version is shown below:
The extended bolt travel MS configuration has not changed.
DETACHABLE BUTTSTOCK ON N/K TRIGGER HOUSINGS
If it is desired to be able to use a 1921/8 style
detachable buttstock on an N/K semi-auto gun, the trigger housing must
be fitted with an adaptor. I manufacture an adaptor to do that. My
Buttstock Adaptor Kit installation instructions are shown below.
Installation of this kit requires milling a mounting flat on the trigger
housing and drilling and tapping the trigger housing. This requires a
milling machine and machinist skills.
If you are planning to install a short barrel (legally) on your N/K gun, you will need to change the barrel, grip mount and forearm or foregrip to TSMG parts. That adds up to several hundred dollars in cost and you still end up with an N/K receiver with its poor quality, super stiff recoil springs, oversized bolt handle and the rear sight in the wrong place. If you are getting the parts from a TSMG parts kit, you end up with several more hundreds of dollars in unused kit parts. I suggest that a better way to go is to order a barreled 2S or MS receiver from me, a trigger housing assembly from Kahr and just make a gun. That requires a little more skill and the finishing of the receiver, but you end up saving money and ending up with something better. If I ever get my trigger housings back in production, that would be the only way to go.
Parts
Kit Semi-Auto
QUESTION : What
is involved in making a semi-auto with my TSMG parts kit?
ANSWER : Unfortunately, to the best of my knowledge, as of this
date (Jan. 2007) there is no ATF approved way of making a semi-auto gun from a
TSMG parts kit as is done with a number of other machine gun parts kits. The
assumption being that the semi-auto gun will have the outside dimensions of the
original, look exactly like the original and use most of the original parts
including magazines. Numrich Arms designed a semi-auto gun years ago that more
or less resembles a Thompson. That gun is now manufactured by Kahr Arms. Neither
of these companies has any connection to Col. Thompson’s Auto-Ordnance Corp.
that invented, developed and manufactured the Thompson Submachine Gun. The N/K
gun is not a true Thompson and not made to the original drawings. Therefore,
very few Thompson parts fit it. Without an approved design to modify the TSMG to
fire semi-automatically, the only option is to make an N/K gun out of a
Thompson. Unless one is willing to spend a lot of money and register the gun as
a short-barreled rifle, it is not a cost effective project. (My book, “Thompson
New Production Semi-Autos” describes this process.) One is better off just
buying the N/K gun. If a detachable buttstock is desired, the most cost
effective way of achieving that is to fit one of my kits to the trigger housing.
If it is desired to have a receiver that is as true to the original as possible,
then one of my MS or 2S receivers can be used. But in the end, it still ends up
as an N/K gun design, not a Thompson. I have a design for a proper semi-auto
Thompson but no time to pursue it. I know others are working on their versions.
Maybe something will come of it.
Semi-Autos (24 Apr 08): For some reason I keep getting phone calls from people wanting to order a machine gun receiver which they intend to finish as a semi-auto. I just don't have the time to go over this again and again. I thought I had made it clear in my various postings that it is not possible to do that. Assuming that the problem is that people aren't finding everything I have to say about this, I have established this new section on this website where everything I have to say about semi-autos will be located. I hope this will be helpful.
Thompson Semi-Autos
(26
Jan 08):
There seems to be a lot of confusion regarding semi-auto versions of
Thompson guns. The yearning for a $20 drop-in semi-auto sear that will
convert a Thompson into a legal semi-auto is understandable but not
realistic. So, I will attempt here to try to explain the factors involved
and the choices that are reasonably available.
Like it or not and regardless of the ingenious designs you may have for a
semi-auto Thompson, we are all stuck with the Government’s design
requirements. Of course, there are no fixed specifications set down in law
that designers can work to, it is the interpretations and political agenda
of bureaucrats that dictate a vague set of requirements that usually are
summarized by some statement like “every case is different so we must
examine the gun in order to make a judgment” or something like that.
However, there does seem to be a pattern that has emerged that we can call
the “requirements” and here it is as I understand it:
1) A new receiver must be used and if configured as a pistol, must never
have had a buttstock style of trigger housing fitted. You can make a pistol
into a rifle but you are not allowed to make a pistol out of a rifle.
2) The barrel must be 16" long if a buttstock can be fitted unless the gun
is registered as a short barrelled rifle. If no buttstock can be fitted and
the foregrip is not a vertical type, then it is a pistol and any length
barrel can be used. However, if a person makes a pistol out of a parts kit
and retains the short barrel, the Government may conclude that the person
intended at some future time to install the short barrel and therefore, has
an illegal gun.
3) The gun must fire from the closed bolt position.
4) The bolt face/firing pin arrangement must be such that if the sear is
removed from its semi-automatic functioning of re-engaging the firing pin
after every shot, the gun will jam on the next cartridge.
5) The receiver must have some means built in to it in order to prevent the
operation of an original full-auto bolt if installed.
6) The trigger housing must not be able to accept a full-auto sear.
7) An unmodified full-auto trigger housing must not be able to fit on to the
semi-auto receiver.
To date there are only two approved designs. The Numrich/Kahr (N/K) and the
Polston. However, there are three choices:
A) N/K. The advantages of this design are that it is the lowest cost and
readily available. The disadvantages are that they solved 5) above by
reducing the height of the receiver by 1/10". This requires the use of
modified box magazines and interferes with the fitting of a drum. Because
the receiver height is not the same as a Thompson, the rear sight is not in
the Thompson position, and Thompson parts are not used, the gun doesn’t look
all that much like a Thompson. Also the quality of the gun is poor.
B) Polston: Polston has gone to the extreme opposite of
N/K. He insists on using virtually every part of the Thompson parts kit to
obtain absolute authenticity even to using the lock mechanism.
The advantages are that his gun is a Thompson in appearance as well as
configuration as is possible within the Government‘s limitations. The
disadvantages are that the gun is complicated and expensive to make. His
insistence that all the Thompson parts be used and extensively modified
where required, makes his gun a virtually custom one off gun which does not
lend itself to manufacturing. That is why he is having difficulty trying to
find a manufacturer to “manufacture” it. A manufacturer would design the gun
for production of say 500 guns with new made parts. By modifying the
original parts instead of making new ones, the task is to modify one gun 500
times. He may decide to do just that so another disadvantage is that gun is
not available any time soon.
C) Richardson: That’s me. I offer an enhanced version of the N/K receiver
(both 1928 and M1 styles) that puts the rear sight where it is supposed to
be and extends the bolt travel so as to reduce the effort needed to cock the
gun. Also, the receiver is made to a much higher quality than N/K. Otherwise
it relies on the N/K approved design. The only disadvantages compared to the
N/K gun is that the buyer has to finish machining the bolt cavity, it is
more expensive and there is a wait. (At one time I manufactured a special
trigger housing for my receiver I called the SA Adaptor-Frame. It solved the
magazine fitting problems of the N/K. It was also made 1/10" taller than the
N/K so the overall dimensions of the combined receiver and trigger housing
were the same as a Thompson and so the gun looked like a Thompson. The
disadvantage of the A-F trigger housing was that it required all special
internal parts. The real disadvantage is that I just don’t have the time to
make them.) A Thompson trigger housing can be modified for use with my
semi-auto receivers or N/K receivers but there really is no advantage now to
doing that since Kahr now offers 1928 style trigger housings and it seems a
shame to damage a Thompson trigger housing.
So, obviously, there is no one simple way to go. The easiest and cheapest
way is to just buy the N/K gun and be happy and use your parts kit to make a
display gun. Well, at least try to be happy but save your money for a real
Thompson unless you see that ad for the $20 drop-in semi-auto sear.
Semi-Autos (9 Dec 07): There are
essentially 3 semi-auto configurations suitable for the Thompson. One is a
“Hammerless” design in which the firing pin is spring loaded. It is retained
in the “cocked” position by a sear mechanism. This is the configuration used
by Numrich/Kahr (N/K) and is common in hammerless semi-auto pistols.
A second configuration is the “Hammer” design in which a spring loaded
swinging hammer is retained by a sear mechanism. When the hammer is
released, it strikes the firing pin, driving it into the cartridge. This
design is used in M16, AK47 and FN-FAL guns and is used in Polston’s design.
A third configuration is the “Split Bolt” design. In this design, the
machine gun bolt is split into an upper portion which incorporates the bolt
face and extractor and a lower portion which contains the firing pin. It
operates similiar to the “Hammerless” configuration. This design is used by
UZI and is the design I used in my semi-auto Thompson design.
There is no particular advantage of one design over the other although when
trying to design a semi-auto version of the Thompson, the “Hammer” design is
the most complicated. The problem is with the ATF approvals. When Numrich
got their approval, the ATF was allowing a bolt with a full feed lip. When
Polston got his approval, the ATF was insisting that the bottom portion of
the feed lip be removed. That did not cause a problem with the UZI but did
with the Thompson because of the position of the ejector on the Thompson.
Polston very cleverly solved the problem with a hinged feed lip (which he
calls the “Rock & Lock”) for which he has applied for a patent. Because of
his patent claim, it is unlikely that anyone will be able to get any design
past the ATF which will not infringe on Polston’s invention. The N/K design
is simple and cheap although poorly designed and made. The Polston design is
complicated and more expensive but retains more Thompson authenticity
especially since it retains the Blish Lock mechanism. My “Split Bolt” design
is irrelevant because I will never have the time nor inclination to put it into
production.
As I see things, the N/K design and the Polston design will both have a
place. Those who want the most authentic semi-auto Thompson they can get
will go for the Polston gun. The majority will settle for the N/K gun. With
that being said, there are still the problems caused by a poorly designed
and manufactured N/K gun and Polston being a ways away from being able to
deliver any hardware. Polston’s website is www.thompsonconversion.com.
My plan is to support Polston’s efforts and try to improve the N/K design
even more than I have. I have redesigned my new 192S and MS receivers to
have a full TSMG bolt travel and use a standard M1/M1A1 Pilot. The 192S uses
my special SA Bolt Handle, redesigned SA Pilots & Plate, special SA Firing
Pin Spring Adaptor and modified N/K bolt. Because of the increased bolt
travel, softer recoil springs can be used but now the N/K firing pin
clearance slot in the trigger housing will have to be lengthened. If I can
find the time to get my Adaptor-Frame SA trigger housings back into
production, I will be able to offer a much improved design over the N/K
trigger housing assembly by incorporating aspects of my “Split Bolt”gun
design and offer a complete SA receiver/trigger housing kit. For the time
being I will offer a complete receiver kit but to mount it on a standard N/K
trigger housing will require the slot modification.
Whereas I am not interested in becoming a gun manufacturer or being involved in large quantities of any thing, I am interested in supplying "Shop" style receivers to those who want to have a special Polston gun. The idea being that I would supply the receiver ready for finishing to the owner of a parts kit and that person would send it on to Polston for finishing. I have already made the first Polston receiver production sample.
NEW PRODUCT (21 May 07):
Semi-Auto 1928A1 Thompson: Tim Polston, who has been working for years on his design for a semi-automatic using a receiver with full size TSMG outside dimensions, has just gotten ATF approval. His design uses most TSMG parts including the Blish lock mechanism. The plan is to utilize a 1928A1 gun kit with some parts requiring modification, some special parts, modified trigger housing and a new receiver. This is not a do it yourself conversion. Don't bother calling Tim. He is trying to figure out what to do with his design approval. He has no facilities for manufacturing the guns. He has been so preoccupied with getting his design approved that he has had no time to figure out what to do next. The important news is that this is the only semi-auto Thompson design utilizing a full dimensioned TSMG receiver ever approved. I had a small part in this and am trying to figure out if I can supply the receivers configured to support the project so I will be on top of any progress and will post news as available.
