posted by mkw
For several years I have been offering my “Display” and “Shop” semi-finished receivers. I do not use the term “80%” because it has no legal meaning nor does it accurately reflect the percentage of completion. Nor do I use the term “dummy” which is usually used to refer to some cheap chunk of metal or plastic that simply provides a base on which to a attach a few gun parts and was never intended to be completed into a working gun. What I make are real gun quality receivers that are not quite finished.
My Thompson receivers are made from steel bars having the same alloy (SAE 1141) and are heat treated to yield the same tensile strength and hardness used in the original guns. The steel is also stress relieved to prevent twisting during machining. The bars are machined on fully automatic, computer controlled machining centers. Computer controlled machining enables edge radii to completely follow the front end contours and to properly radius the 1921/1928 drum slots, bolt handle slot and magazine cavity edges. To assure the most accurately made receivers, centerline coordinate machining is used with one set-up for all four sides, edge radii and interior in order to eliminate tolerance and error cumulations caused by changing set-ups and reference lines. The quality of these receivers exceeds the originals made by Colt, Savage or the real Auto-Ordnance Corp. (Bridgeport) or anyone else.
I have learned from buyers of my receivers that there are essentially two configurations of receivers wanted. The first is a receiver that appears from all outward respects to be a working original gun receiver. It should accept as many of the original gun parts as possible. Where it is not possible to fit gun parts, the receiver must be able to accept display parts that will make the “gun” appear to be complete. Also, the receiver should not require any additional machine work to assemble the “gun”. The second is a receiver as just described but with as many additional machined original gun features as possible so that the receiver can be finished into a working gun with the least amount of machine work possible. And, QUALITY, QUALITY, QUALITY!!! The first configuration describes my Display receiver. The second is one I have never built although I offered lock ramps and bevels as an option.
I have, therefore, decided to reconfigure my line of receivers by discontinuing my original Shop and Display receivers and offering the ESF receivers.
ESF stands for “Enhanced Semi-Finished”. ESF receivers are available in two configurations. The Display and the Ultimax . Ultimax stands for “the ultimate maximization possible of Thompson gun features that can be incorporated in an unrestricted semi-finished non-gun receiver”.
The Display ESF configuration includes every feature of my original Display receivers. I have elected to retain the name for that reason and also because “display” describes the purpose of this receiver so well. However, in addition to all the features of the original Display receiver, I have added the enhancement of a pocket in the rear of the bolt channel area to enable me to drill and countersink the holes for Thompson sight mounting rivets. Therefore, the rivet holes are finished. Receivers will no longer be provided with special sight mounting screws because there are no threaded holes. Instead, the buyer has the option of installing the rear sight with Thompson sight rivets or bolting (through the rivet holes) the sight onto the receiver. I offer both the rivets and bolts/nuts in my catalog. I think this will satisfy everyone. Also, the new Display ESF receivers have been further enhanced by having more finish machining work done to the interior. There will be no machined options offered for the Display ESF receivers other than the early Colt squared end actuator slot and M1 bolt handle location.
The Ultimax ESF is a Display ESF receiver with every missing Thompson gun receiver machined operation added. The front and back ends of the bolt channel are finished, including the expanded rear section of the 1921/1928 receiver that accommodates the breech oiler. The breech entry chamfer is finished. Lock ramps and bevels are finished. No machined options are available other than the Colt squared end actuator slot and M1 and M2 variations. The Ultimax is a complete Thompson receiver except that there is a solid section in the middle of the bolt channel. Previously, any machining operation in the bolt channel which could not be completed was not done at all on the semi-finished receivers. Those operations would be left for the person who would be completing the receiver. Ultimax changes all that by having every machining operation done. To do that, Ultimax introduced the concept of “interrupted cutter path machining”. This means that a cut that normally starts at one end of the bolt channel and terminates at the other end will be started and stopped as it normally would be in a working Thompson receiver. It is only in the solid middle section that the cut will be interrupted. The Ultimax receiver can be assembled as a display “gun” exactly as the Display ESF can be. ESF receivers can not accept a bolt since there is a solid section of steel left in the bolt channel but will accept my Display Pilot and Bolt Handle Kits.
Those who have the license to finish the receiver into a working gun will find the Ultimax to be the best semi-finished receiver available. All of the time consuming and difficult machining operations have been done. Finishing the Ultimax receiver requires the solid center section of the bolt channel to be removed. But what needs to be done is obvious since every interrupted cut starts and stops as it would normally. It is not necessary to analyze drawings to set cutter positions - just continue the interrupted cuts using the beginning and ending portions as guides. Those building up a display gun with an Ultimax receiver will have the added enjoyment of understanding how their “gun” was designed to work by simply examining the receiver - it’s all there!
Only two cutters are required to finish an M1-style Ultimax ESF receiver: a 3/4" diameter, 4 flute, 1-3/8" minimum cutting length, coarse tooth, roughing end mill (TIN coated and M42 steel is recommended) available at most any industrial supply store; and a 1/2"diameter, 4 flute, 1-3/8" minimum cutting length, .030" corner radius end mill (coated carbide is recommended) which is offered in my catalog. 1921 style Ultimax ESF receivers require the same two cutters plus a standard 1" diameter, 3/8" wide, ½" diameter shank Woodruff keyseat cutter (preferably with an added .030" bottom corner radius) to finish the center section of the side slots.
ESF receivers are available in all standard Thompson models and some additional models of my design. 1921/1928 and M1/M1A1 models are available in both the Dis-play ESF and Ultimax ESF configurations. The Models 1921 and 1928 are dimensionally identical as are the Models M1 and M1A1. The Models 2M2, 2MM, 2S, M2 and MS are available only in the Ultimax ESF configuration.
The 2M2 receiver is my redesign of the 1921/1928 receiver with the trigger housing rail walls extended all the way to the back end of the receiver to increase rear end strength and the pilot hole sized like an M1 but in the 1921/1928 position. This receiver is designed to be finished to accept a 1921 or 1928 bolt/actuator/lock assembly but eliminates the oiler which, arguably, never really worked. A modified M1 pilot and Richardson 2M2 Urethane Buffer are used for better recoil spring control and true buffering. In my opinion, this creates the ultimate 1921 or 1928 gun because it has all the benefits of the 1921/1928 lock mechanism with the ease of assembly of the M1. It also is designed to be fitted with my Screw-On Grip Mount in lieu of the TSMG design.
The 2MM receiver is a 1921/1928 receiver except that the pilot hole is sized and positioned like the M1/M1A1, the bolt handle slot has been moved slightly rearward and the trigger housing rail walls have been extended all the way to the back end to increase rear end strength like the 2M2. It is meant to have a bolt channel identical to an M1/M1A1 except that it has side pockets similar to a 1921/1928 receiver for weight reduction. This combination enables an M1 or M1A1 bolt, modified to have a top mounted bolt handle with one of my kits, to be used for simple and more reliable (especially with blanks) slam fire operation. This is particularly advantageous to studio prop shops, shooting galleries and other NFA manufacturers who wish to make an operating 1921/1928 style gun with a minimum of time and cost.
The M2 receiver is my redesign of the M1/M1A1 receiver. The bolt handle slot is located on top like the 1921/1928 receiver and uses the same modified M1 or M1A1 bolt as the 2MM receiver. The trigger housing rail walls are extended to the back like the 2M2. The upper sides are continued forward to the front end to produce a sleeker looking receiver. The nose of the receiver is relieved on the sides below the barrel area to better match both horizontal forearms and vertical foregrips. It also uses my Screw-On Grip Mount. It is available in two versions: 1) Model M2-M has the M1 rear end shape to match M1/M1A1 trigger housings and 2) Model M2-2 has the 1921 rear end shape to match 1921/1928 trigger housings. It is also available with the top side edges non-rounded in the rear sight area to accept a Lyman adjustable rear sight. This receiver is interchangeable with any TSMG receiver.
For those who want to build a semi-auto gun, I offer my 2S and MS 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.) Like the N/K receivers, these receivers are 1/10” less high than a TSMG receiver. They are interchangeable with N/K 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 receivers are meant to have a bolt channel 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 to use the extra bolt travel to absorb the recoil rather than to depend on very stiff recoil springs. It also provides room for a urethane buffer. These receivers have the extended trigger housing rails like the 2M2 receivers. They require a modified N/K Bolt and Firing Pin. All other bolt channel parts are special Richardson designs and manufacture. The 2S and MS receivers also differ from their N/K counterparts in that they use my Screw-On Grip Mount, 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.
Prices (Markings, Colt square end actuator slot, M1 and M2 variations, sight fasteners, added parts, services, etc. are at extra cost. Bluing is included.):
Display ESF receivers: Models 1921/1928 $585 Models M1/M1A1 $585
Ultimax ESF receivers: Models 1921/1928 $885 Models M1/M1A1 $685
Model 2M2 $865, Model 2MM $750, Model 2S $750, Model M2 $685, Model MS $685
For more information check my website: www.Thompsonsmg.com
Edited by Doug Richardson, 15 November 2012 - 04:28 PM.