Here's How We Are Building Our Nieuport 11s, Page 12 -- part III John's finished  Lewis machine gun
Probably more time was spent than really needed for the Lewis machine gun. The construction log lists nearly 70 hours spent making it, including the small parts design. However most of the work could be done on the kitchen table where the temperature was in the 70s. Outside the temperature was usually hovering around 100 degrees -- and in the hangar around 110-120. Note that most of the tubing metal, bolts, fittings, wood etc. were good items scavenged from my "junk" bins and drawers.
Front gun mount and sight
Rear gun handle
This is the finished front gun mount and sight. This is the rear gun handle. The ABS handle holder was fitted with a .080 aluminum plate (epoxy glued in). Then Plastic Wood was used to fill in any spaces. A 6061 T-6 .058 aluminum strap 8.5" long by 1.5" was made and shaped to hold the 3.75" handle which was from a .75" OD birch broom handle. The strap was glued onto the handle holder with 5 minute Epoxy. Two 3/16" x  7/16" long AN machine screws fastened the handle assembly to the receiver. 
Lewis gun grips
Magazine handle
These are the gun grips. They were fashioned out of two 2" x 4" pieces of 6 mm Okoume. After smoothing, shaping and sanding they were coated with walnut stain and Tung oil. This is the magazine handle which goes on top of the magazine. The strap and strap holders were taken from a duffle bag. Loctite Blue was used on the screw threads. The strap holder was fashioned out of a piece of .058 4130 steel.
Internal workings of Lewis gun
Two views of the finished Lewis machine gun
This is a view of the "guts" of the machine gun. A section of .080 7075 aluminum 8.5" long x 1.125" was carefully bent as a support and wraps around from point H to just past point M. Half of it (sideways) was slipped into this half of the shell (after removing some foam material with an X-Acto knife). Five minute epoxy glue was applied before it was slipped in. At point M a 2-13/16" x 1/4" AN bolt was put through a hole in the support and then J-B Weld was used to secure its head. The end of the bolt has a hole for a cotter pin/tie wire. The bolt is used to secure the magazine. Also a copper wire was fastened from the bracket to the combustion chamber. The gunsight, being the highest point on the aircraft, will pick up static electricity even at 70 m.p.h. Even this could happend -- click HERE! At point H two 3/16" x  7/16" long AN machine screws were put for the gun handle bracket. Two holes were tapped in the bracket. Under point C a 3/16" hole was drilled in the bracket for putting in the rear sight eye bolt. This also secures the rear of the flat magazine holder. The dowels at A, B, C, D were glued in this side with 5 minute epoxy. Brass screws also fastened the ABS plastic shells to the dowels. The 1/2 inch dowel lengths are: A: 24 mm; B: 23 mm; C: 41 mm; D: 31 mm. The assembled Lewis machine gun. Two views. The shroud is fastened with four tiny screws to the ABS receiver but that isn't really necessary since the cooling fins inside the shroud are what hold the shroud in place. Note that the gun weighs a little less than six pounds.
The control section of the gun -- made to fit in the wing so that the cables won't be in the way. Note that the valve will have a limited life since Viton or other valve materials suitable for propane will be deteriorated by oxygen -- the mixture going through the valve is at least 70% oxygen with the remainder propane. Perhaps heavier heat sinks than necessary were used on the oscillator circuit board but too much is better than not enough. Also note the vent tubes -- these will go out the wing. The inlet tube comes out just below the wing.  An EAA 172 friend who flies AT-6s and has friends who fly P-51s with gas guns told me that more than one P-51 with a gas gun has had its wing explode because of accumulated explosive gas in the wing.  The Lewis machine gun firing. Note the length of the flame front. For safety's sake don't let anyone go in front of the muzzle! Any object (such as a bug) inside the muzzle will be shot out like a bullet. The diagonal braces made from 1/2" 6061 T-6 tubing add to stability and realism.

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