Here's How We Are Building Our Nieuport 11s, Page 10 -- part I of John's Lewis machine gun
To take a break from working on the wings, John decides to build the Lewis machine gun which goes above the top wing. Rather than the "dummy" gun that is in the plans, he is building an oxygen/propane gun from plans and vacuum formed ABS gun "shells" obtained from Ted Callahan. Though Ted drew up great plans, certain small aspects, such as the mounts, dowel fasteners, sights etc. were not described in detail. On this page and the next two, are photos of these and also some gun modifications and enhancements.
Testing the guts of the gun
The flashback arrestor, combustion chamber and barrel
John tested the gun's gas guts outdoors (in a safe place) after building the high voltage circuitry and all the gas plumbing. He found that the barrel temperature rose to about 150 degrees after a long 10 second series of bursts. The photos below show how he made cooling fins for the barrel. Note that in our EAA 172 chapter, several of the members are veterans of World War II and the Korean war and flew P-51s in combat. They told us that they never fired the P-51's machine guns more than a 2 or 3 second bursts -- because of overheating. The flashback arrestor was bought from Grainger's -- make sure you don't get the cheap acetylene arrestor but the good arrestor/check valve. A cheap one like the one used with most torch handles won't shut completely and could cause an explosion or at least a fire in the line and destroy your solenoid valve (don't ask how we know!). This is a Purox FR20 which cost $ 31.35 and could be bought separately. The spark plug is an SP-34 lawnmower plug. The spark plug wire was some TV type high voltage wire (used for the picture tube).
Cutting out six cooling fins
Securing cooling fins to barrel
Six cooling fins were cut out of .035 6061 T-6 aluminum. These would have cut-outs made on the bottom to allow the screws holding the front gun mount to pass through. The round fins were 2" in diameter and had five .5" holes cut into them to allowing air to pass through. The bottom two holes were cut out to the edge so the shroud, with bolt heads,  could pass over them. After being thoroughly cleaned, the barrel was set up outside perfectly straight and level. Then the cooling fins were aligned so they would be hidden by the cooling shroud (which had six horizontal slots cut in it to allow for the hot air to escape). Then, J-B Weld was used to secure the fins to the barrel. J-B Weld can withstand temperatures to 600 degrees Fahrenheit. 
The finished barrel assembly Front of gun with cooling shroud in place
The finished barrel assembly. Note that  the special cooling shroud nose piece goes around the front of the cooling shroud. A potted meat can (with all but the bottom 1/2 inch removed) fits perfectly! The front portion of the barrel was blued with Hoppe's gun bluing, then oiled with gun oil . The flash arrestor part had been silver soldered on before J-B Weld was used to secure the six cooling fins. The part of the barrel that will be hidden by the shroud was painted with Krylon HT 1305 high-temp black spray paint. The barrel itself was a 4130  .5" OD x .049" wall steel tubing 21" long. The front of the gun with the cooling shroud in place. On the next page we'll show you how we made the muzzle "flash arrestor" as well as the sights and gun mounts and also show you the whole cooling shroud that really works.

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