The drawings on following pages may be used if the bolt is to be machined using a lathe, (See Figure W). In the interest of ensuring the bolt is as strong and durable as is reasonably possible, we must machine it from a suitable steel. We do not want to harden and temper the bolt following machining, due to the inevitable 'technicalities' involved in doing so. Although hardening would be desirable, for the average hobbyist, it would be an unfeasible proposition. The actual size (diameter) of the bolt would necessitate the use of a suitable heat source such as a fire brick arrangement or a small furnace in which to heat the component to the required hardening and tempering temperatures. Not to mention the ability to use such techniques and equipment. Small parts such as, for example, a sear, trigger or firing pin are quite easily heat treated using nothing more than a propane gas torch (available from any hardware store) and bucket of oil or water in which to quench the job. The larger component does pose problems for the average individual.
All is not lost however because steels are available in the pre-hardened and tempered conditions. In other words, the steel comes "off the shelf" in a pre-hardened condition, while at the same time being 'soft' enough to machine. These steels are suitable for our requirements (and many others) where a reasonable degree of shock and wear resistance is required. Two pre-hardened steels I have found suitable (and that seem to be reasonably easy to locate) are 709M40 (EN19T) and 817M40 (EN24T). You will need to purchase such materials from a 'special steel stockholder', so look in the 'Yellow Pages' under 'Steel Stockholders' for a supplier in your area. Searching the 'Net' is also a good idea. Such steel is rather expensive in relation to, for example, a mild steel, especially if you have to have it delivered, but you may be able to purchase a short length as a 'sample' or 'off-cut'. Always check when purchasing such steel that it is in 'T condition' meaning it is sold in the pre-hardened state. Some steel manufacturers also advertise their own brands of 'special steels' in the pre-hardened condition, and if you decide to purchase one of these, you should ensure the steel is suitable for your purpose. Generally speaking, it must fall into the high tensile, shock and wear resistance category. The alloy steels I have listed are a good example of these requirements and are reasonably easy to locate.
Machining the bolt is a straight forward turning procedure for the lathe owner. Start with a section of round bar, at least 26mm in diameter, and machine the bolt to the following dimensions:-
Referring to Figure 'A', Outside diameters (OD) Bolt overall length (OAL) is 131mm. Front section (A1), turn to an OAL of 53mm and 13mm OD. Turn remaining length (A2) to an OD of 26mm, ideally.
Figure 'B': Using a 5.5mm diameter drill bit, the mainspring/guide recess (B1) is machined to a depth of 100mm. The recess is then re-bored to a depth of 74mm using a 9mm diameter bit.
Cartridge Recess. The cartridge recess (B2) is machined to a diameter of 9mm and a depth of 2mm.
Figure 'C': Ejector bolt slot. Machine slot (channel) to 32mm in length and 3mm width (C1). Slot depth is 4mm (C2). The slot may be machined at any point on the bolt radius at this stage.
Figure C3, Bolt handle position (looking into the cartridge recess). Drill bolt handle hole at a 45 degree angle adjacent to the ejector bolt slot to a depth of 6mm. Tap hole to accept a 6mm diameter socket screw.
protrude 1 mm from recess face when fully seated (D2).
Figure 'E', .380 bolt. All dimensions for the .32 bolt apply equally to the .380 bolt, except for cartridge recess (E1) 9.7mm to 10.0mm diameter, and front section (E2), 13.5 mm 'OD'.3
Figure 'F', Position the bolt handle hole 50mm from the rear face of bolt.
Figure 'D', Firing pin hole. Drill to 1.5mm diameter (D1) and 12mm depth (D2). Pin consists of 1.5mm dia' drill shank 13mm in length. Retain the pin using bearing adhesive or similar product. Pin must
3 Note: a certain amount of 'hand fitting' may be required to ensure the bolt will function reliably.
(All measurements in millimetres)
.380 BOLT DIMENSIONS
(All measurements in millimetres)
1. SLING LOOP
2. GUIDE ROD
5. BOLT HANDLE
6. BOLT STOP
8. BARREL RETAINER
10. MAGAZINE WELL
12. MAGAZINE STOP
13.BASE PLATE SPRING 14.SPRING CATCH
15. CATCH BOLT 16.SEAR SPRING
The following machine pistol design is similar to the .32/380 Machine Pistol, except for an alternative bolt and mainspring design and slightly different receiver dimensions. The firearm cannot be constructed entirely by hand but requires the use of a lathe to construct the bolt and recoil shield. However, the firearm is easier to build due to a simpler bolt design. The upper and lower receivers are constructed from the same 30 x 30mm tubing discussed earlier. The following plans are an alternative construction method:-
The lower receiver templates are used in the usual way and the recess positions marked. The lower receiver being 11 1/8" (283 mm) in length. When the receivers are temporarily clamped together (using the two hose clips we used earlier), the breech end of the upper receiver must overlap the end of the lower by 6mm.
The bolt is a simple assembly consisting of a 7" long section of TV' diameter high tensile bolt, and a series of six Va" shaft lock collars. The Vx" bolt section should i have a tensile strength of 12.9 ideally. First, remove the bolts head and thread. Figure 'A', and using a lathe, trim each end of the bolt until it has an overall length of 4 3/8" (111mm), Figure B'. The cartridge recess and ejector slot are now cut (so suit calibre) into one end of the bolt section. At the opposite end, a series of six Vz" collars, (Figure 'C') are fitted and retained with bearing adhesive or a similar product. The bolt handle is now screwed into the third collar from the rear of the bolt. The third collar remains moveable to allow the bolt handle to be adjusted as necessary to align with the bolt handle slot.
The recoil shield is machined from a section if round bar. As shown in the illustration, (Page 8), the shield has an overall length of 68mm. A simple piece of ordinary mild steel is perfectly adequate for this. The shield is secured in position with four 6mm diameter socket screws.
The mainspring cannof be successfully coiled by hand due to the heavy gauge of wire required to make the spring. There are two options available. The first is to locate arid purchase a spring of the correct dimensions, and the second is to have a spring specially made. Many spring manufacturers hold large stocks of ready made springs, and it may be possible to find a spring of the correct dimensions. However, the second option is by far the easiest. Having a spring made may sound like an expensive option but the cost is quite reasonable, especially if the spring is made by one of the smaller manufacturers, who may even coil the spring while you wait or for next day pick up. The main cost in having a spring coiled is in the setting up of the machine, rather than in the cost of the material used. It is usually possible to have a one metre length of spring coiled (out of which we can cut about six individual mainsprings) for about £15. This means that each spring costs less than £3 each, not bad for the firearms fourth most important component! Rather than spending time looking for the correct spring "off the shelf", it is far easier just to supply the required spring dimensions to the manufacturer and have the spring specially made. It is quick, easy and relatively cheap. For the Mktl machine pistol we require a compression spring, 25mm in diameter (OD) and coiled from 15 gauge wire. The spring should be coiled from standard carbon steel wire. Once the length of spring has been acquired, it may be cut into 6" lengths, this being the correct length for use in the Midi machine pistol. Alternatively if you wish to spend a few pounds more, the manufacturer will automatically cut the spring into 6" lengths as it comes off the machine, saving you an extra job. Look under 'springs' and spring manufacturers' in 'yellow pages'.
Note: This template is not drawn to scale and must be enlarged by 25% using a photocopier. After enlargement, the overall length of the template should be 282mm. If it is not, the template can be enlarged or reduced as necessary until the 282mm measurement is achieved.
Cut out and remove shaded areas.
(Note; Hole diameters not to scale)
MK11 UPPER RECEIVER RECESS POSITIONS
(All measurements in millimetres)
CENTRE LINE LEFT SIDE
The upper and lower receiver assembly
(Measurements in millimetres)
With the upper and lower receiver assembly clamped together with two hose clips, the upper receiver must overlap the lower by 6mm, as shown at 'A'.
The slot for the trigger 'B', is positioned 58mm from the rear end of the receiver and is 17mm in length. The slot for the trigger guard, 'C', is positioned 51mm from the front of the receiver and is 3mm in length and 12.7mm (1/2") in width.
LOWER RECEIVER ASSEMBLY
The trigger guard, grip, and socket screws are secured in place using silver solder at points 'a' 'b' c' and 'd'. The socket screw 'd' allows the sear spring to be attached to the receiver.
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