On Sun, 23 Apr 2006 07:39:50 GMT, Gunner
wrote:

Anyone got a source for plans for making your own air rifle? Id like
to machine one. Just about any type. Think it would be a fun project.

Something run or charged from CO2 welding tank might be fun.

Gunner


this is an interesting project.
I've been trying to accumulate enough scrap to make one for some time.
still working on it. damn the chinese! there are no scrap merchants
left in my neck of the woods who arent a siphon for material to china
these days. ...anyway.

there are two schools of thought regarding air rifles. the predominant
school says that the gun must be heavy to make use of it's inertia for
stability. I think that that is erroneous myself and I have won
against the most expensive guns using a much battered club .177 air
rifle. it is a a comparatively light rifle, the Sharp Innova made in
japan. it is not a break back so the sighting on the barrel remains
accurate. on the club ones an old martini henry ww1 rifle adjustable
rear sight was fitted which was superb. (the kids just remembered
their traverse and elevation settings and could pick the rifle up
after someone else and be back shooting in a moment)

The mechanism of this rifle is superb, very simple, and I originally
though would be easy to make. (I'm sure it is if you amass the right
materials.)
I had a chance to measure one and from this I have an incomplete
sketch that I will attempt to upload to the drop box later tonight.

the barrel is in brass, 9.4mm (.37")od with a bore of .177" or 4.5mm
thereabouts. it sits in a larger protective tube made in light steel
which can become a little battered in use without affecting the barrel
accuracy at all. the barrel sits about 5 - 10 mm proud of a parallel
tube that contains the air pump and receiver. a short tube extends
from the barrel down to the receiver. the tube is screwed into the
barrel but just sits pressed to the outer surface of the receiver with
an o ring making the seal. the aft end of the barrel is sealed by a
bolt action which has a tapered pin extending from it to engage and
align the rear of the air pellet.when home the bolt seals the barrel
rear with a very small chamber formed behind the pellet. a 4mm dia
hole extends from this chamber down to the receiver through the
interconnecting tube.

(I never recorded barrel lengths because I was after a shorter action)

the air pump sits below the barrel. it is formed in a steel tube of
22mm od and 19mm id. at the foresight end and hanging down vertically
when about ready to commence compression is a hinged lever. 4 1/4
inches from the hinge fulcrum is a joint to a short lever that returns
back to the piston mechanism and actually drives this through a slot
in the underside of the tube. the piston mechanism is just two pistons
interconnected by a screw adjustable rod, the front piston has a slot
machined in it which accepts the short driving lever, using a roll pin
as the joining pivot. the actual pumping piston is in brass with an
oiled bucket seal on the end.(I think it was leather) the pumping
stroke is 4 1/4 inches.
when this lever is pulled fully back it engages a detent which holds
it against the barrel. in the detent position the air piston is fully
home against the front face of the air receiver.

the air receiver is a 19mm dia cylindrical brass piece, it is sealed
to the pumping tube by a small o ring about a millimeter back from the
front end. the front end has a conical face. this is sized so that the
centre of the piston can sit almost hard up to it and it provides a
small space for the bucket seal to sit without being crushed.
in the centre is a small hole leading back into a chamber of maybe
3/8" dia. the front is sealed by a spring loaded ball. the compression
of the piston unseating this ball to allow compressed gas back into
the receiver. the complete receiver is 55mm long with about the rear
15mm taken up by the firing mechanism. the receiver chamber is
probably 3/8 or so by maybe 30mm. (i never fully disassembled it)

the rear of the receiver is a screw in piece, 19mm dia by 14mm thick
with a 10-15mm nose piece protruding from it. this nose piece is
threaded and screws into the back of the receiver chamber.
through this piece is a polished/reamed 4mm dia hole. in the centre of
this tube section there a 3 o rings sitting side by side to seal the
pin. 10mm forward of the back face of this 14mm piece there is a
transverse 4mm dia hole leading up to the interconnecting tube from
the barrel.

the air control pin is 45mm long and basically is a 4mm dia polished
rod with a 7mm dia land 2.5mm thick sited back 17mm from the leading
end. forward of this land the pin engages precisely into the rear of
the receiver and is sealed by the o rings just forward of the
transverse interconnecting hole. I cant recall what locates the
receiver but I think it was a 6mm dia socket head capscrew up from the
underside into the rear piece which may have been steel.

a 16.5mm od washer 2 mm thick sits against the rear of the 7mm dia
land on the firing pin. behind this is a spring, 9mm dia in .54mm
spring wire.

right at the rear of the piston tube is an internal thread. screwed
into this is a 4mm blanking plate which has a 4mm hole in it to guide
the air control pin. forwqard of this is a hard steel washer 6mm thick
with a 12mm id hole, the purpose of which is to provide a home for the
spring as the air control in drives back, preventing it being crushed.

mounted in the stock immediately behind the pump barrel is the trigger
block. the trigger sits below the trigger block, is pivoted roughly in
its centre axis in profile, with a pawl on the rear edge which pushes
up against the trigger block in turn pushing it up. there is an L
shaped apperture plate which sits flush against the front face of the
trigger block. the L extends back over the top where a spring sits to
push it up from the top of the trigger block.
the apperture plate has a 5mm by 6mm aperture.
the trigger block has a 6mm dia hole back into it with a polyurethane
block at its deepest point.
at rest the apperture plate sits behind the air control pin and blocks
its rearward movement. the hole in the trigger block sits below the
pin axis and so provides a second safety.

when the air pump is used the pressurisation pushes the pin back
against the apperture plate, but all remains sealed at this point. in
competition shooting on a 10m range 2 pumps are sufficient. it can
take up to 11 pumps.

when the trigger is eased back the trigger block is pushed upward
moving the 6mm hole into position to receive the pin, the apperture
plate stays still with the up spring being compressed. as the trigger
pressure is increased the apperture plate is lifted until it
disengages the pin. pressure fires the pin back, collecting the 16mm
washer and return spring, at its rearward travel the polyurethane
block decelerates the pin to a standstill. while this is happening the
air rushes back with the pin, turns up through the 4mm hole and fills
the small aperture behind the pellet driving it forward.
with the pressure gone the return spring pushes the air control pin
back to its forward position and gravity drops the trigger block back
into position. the trigger block is steel, 21 x 9 x 14mm in size. the
apperture L plate is 2.5mm thich hardened steel.

ok? hopefully that will explain the sketch which I will now attempt to
put in the dropbox.
Stealth Pilot