Logan's Run: 
The D.S. Pistol
(DS = Deep Sleep)
By Richard A. Coyle
(Note all photos are real movie props.)
This was a very interesting Movie Ray Gun.
It shot greenish FIRE out the muzzle. The POP and SIZZLE sound of this weapon was
enough to freeze any runner in his tracks.
And the look of it. This was a very real look Sci-Fi ray gun. Long thin
and black. And even with what looked like a upside down sight fin on the muzzle,
and none on the upper part of the weapon, in fact there seemed to be no sighting
device of any kind, it still was deadly accurate in the 
hands of the Sandman police as seen in the "Great Hall" when Logan
and Francs tormented a runner on purpose with near misses.
OK so how did this fire-breather it work? Carbide and water - the same stuff used in
old-time miners' helmets. When mixed with water, calcium carbide gives off acetylene gas,
which will burn just like a torch. The closed chamber at the rear of the gun would produce
a fair amount of gas at moderate pressure, so getting the rear cap on after throwing in
the reactants the was a real challenge. In fact, it generated enough pressure that that
the propmakers had to add a booster spring to the valve in order to keep it closed. The
trigger simply opens this valve, thereby allowing the gas to flow through a tube to the
front of the gun and shoot out a small jet soldered into it.
The jet of gas would hit the front of the muzzle and fan out, hitting the red
hot glow plug mounted into the bottom front end of the muzzle just in 
front of the fin. The glow plug was powered by a 2.5 volt, rechargeable, lead
acid battery (Gates "D" size) mounted within the pistol grips. It
was turned on and off by the toggle switch just in front of the trigger on the
underside of the pistol's frame.
Later models used on the TV show used a different type of switch. There was a story
going around at one time that Richard Jordan burned his leg pulling the gun out of its
holster. This may have prompted the change in switch design, in order to improve safety by
delaying the firing of the glow plug.
It is also a fact that many recreations and the one genuine working prop I fired (shown in
these photos) leaked gas around the valve on many test firings. I believe that the
expressions of the actors' faces and their tight grip of the pistol suggests that they
were concerned about this flaw during the filming of the action scenes where they had to
actually fire the guns.
So,
what were they made of? The pistol frame was constructed from band-sawed aluminum
plate. The pistol grips on the two I have held were made of automobile body
filler putty, also known as Bondo®. The trigger and rear gas chamber were made
of brass. The side panels and the muzzle's front fin were made of phenolic resin
plates. The tube body and the muzzle itself were made of aluminum tubing. Lastly,
the triangular holster 
plate and mounting stud were apparently made of mild steel, because they were
welded together.
One note about the front muzzle: on the working movie prop, the hole in the front
appeared to have a washer pushed in with gasket of duck tape in the bore in order to neck
down the large diameter of the tubing to the smaller hole seen. On later models, like
those used in the TV version, this feature was machined as a part of the end cap. It is my
belief that they wanted to use the larger bore of this muzzle, because in Hollywood bigger
is better and certainly more intimidating as a gun, but they found that the gas just shot
right out the front without hitting the glow plug and lighting. Thus, a modification to
the bore was required, so the washer was added to cause the gas to fan out and positively
hit the glow plug.
