The 7/8ths Scale Gas-Powered
Lewis Gun Replica
The gas-powered Lewis replica was designed to safely mimic the sound of a firing
machine gun without the use of blanks or other ammunition. Oxygen and propane
(or MAPP) are mixed together then ignited rapidly in a small combustion chamber
to make the noise. It should be noted that the gas-powered Lewis was not intended,
and cannot be adapted, to fire any type of projectile. As with any project dealing
with potentially explosive gasses, great care must be used to ensure safety.
Brief Overview
Marvin Story's
gas gun design was the basis for the effort. Some of the gas gun components
were separated to allow the remaining components to fit into the plastic Lewis
shells. The components separated from those in the Lewis shells are installed
in an accessible wing locker beneath the replica gun.
In summary, oxygen
and propane are admitted to the small combustion chamber through solenoid valves,
a mixer, and check valves/flashback trap. The combustion chamber houses a standard
automotive spark plug that is driven by an automotive coil being pulsed by an
NE555 timer circuit. As the gas mixture ignites, the expanding gas pressure
causes the flashback trap to close momentarily cutting off the gas supply. As
the pressure subsides, gas is readmitted to the combustion chamber for another
cycle. "Firing" is controlled by the gas supply as the spark is left
to run continuously. The speed of the 555 timer is controllable therefore the
'rate-of-fire' can be adjusted with a potentiometer.
Images 1-4 are internal pictures,
images 5-9 are external, assembled pictures.
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1. A view of the gun housing and internal components.
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2. A closeup view of the gas-firing mechanism assembled inside the left
half of the gun housing.
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3. A view of the right half of the gun housing, showing the routed-out
foam ready to accept the gas components.
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4. A closer view of the internal gas components.
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5. A profile view of the assembled and painted gun.
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6. A closer, detailed view of the gun body and cartridge carousel.
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7. Another complete view. Realism is achieved with gun-metal black paint.
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8. Overhead view of the entire assembly.
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9. Overhead view of the carousel. Those familiar with the design know
how hard it is to reproduce this component.
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