This is straight
to the point
Safe to safe and punch out
Remove
Stock nut action
Allen on breech
Rear sight
Barrel band screw
Barrel (twist back and forth)
Phillips in breech Trigger Breech
Hammer pins
Rear caps
Stock stud
Valve screw
Hammer Assembly
From front cap side drive out the valve, don't
worry about
the seal it's going to be replaced
anyway.
The stock stud
nut will come out with it.
Allen in the back of the bolt
Handle
Bolt 
QB-78 Major Mod Diagrams
Courtesy of Craig
Pitts- Co2unes |
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|
22xx Breech |
22xx Tube |
Barrel Band |
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|
Barrel Tube
End |
22xx Cover |
QB Barrel |
| |
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|
QB Tube End |
(Click
above images for larger
view)
This is the way I
tune them. It's been tested and proved by 100's of
guns, as said in the beginning; any variation to
this process is on you. Basically the tune is a port
and Valve job. We're going to knock most of the
sharp corners off and angle the 90deg turns and open
the ports. Any 90deg the gas sees, it sees as a
restriction. Some of you motor heads just went
AH-HA! I see. You see the basic Co2 gun is just a
single stroke single piston engine, Piston =Pellet,
fuel = Gas. That's it. Just like a hotrod the more
flow the more go and remember the more go the less
MPG or in this case shots per charge. With this tune
you should expect .22 upwards to 740fps 16fpe .177
800fps 12fpe, 30 good shots depending on Temp and
pellet weight. No joke, no jive, just fact!
Tune:
Valve Disassembled
First get rid of the packing and screen, the newer
guns don't use this and it's is a major restriction.
Stem:
I angle the stem in the lathe by holding the head
from the seal side,
turning the compound to 10-12 degs.
Taper the head to about .200-.187" at the point.
Turn it around and break the sharp edge on the seal
side, don't get over zealous. I little goes a long
way. Make sure you clean the filings of the seal.
Click
for larger pix >>
You can open the seat area to #7 drill .201" and
with a long 30deg Countersink dress the seat to a
smooth angle. The angle isn't a must but it give 3-5
fps.
Exit port though most new guns
are opened up and angled if you have a older gun
,the port can be open up to .187 no bigger, any
bigger and she won't seal and angled back. Don't cut
the seat on your angle ,if you do your done go on
home and order another gun.
Top Drill .125" .125" from the edge in the slot.
Clean up the burr inside.
<< Click for larger pix
Pierce pin:
This can be done on a bench grinder, angle back the
nose to just blend into the point about 30degs. This
is to guide the pin up through the top hole. If
you're bulking the pin can be eliminated
completely. Click
for larger pix >>
Replace the body seal and reassemble don't tighten
the valve body. This will be done this the Co2 tube.
To make sure every this is hunky dory, press the
stem down on a hard surface to compress and open the
valve look for the pin to come up with no major
binding. If it does tear it down and reassemble.
Two ways to do this is by hand and machined.
In the lathe part off the tip to just behind the
port, Drill #42 drill to .625 deep. Cut the sharp
end off the #6 finish nail and dress a lead in.
super glue the nail in, Cut off to no longer than
.500" dress the probe to a nice radius. The .22 cal
is done.
On the .177 your going to open up the o ring groove
to a groove .070" wide x .040 deep. I use a straight
pin as a tire iron to get the o ring on. Have a
couple extra they're a bear to get on.
Hand method:
Drill the end
of the .22 to 5/32"
Drill the end of the .177 to 9/64"
This can be done in a drill press with a
vice.
Bolt Probe
Click
for larger pix
Barrel:
This is the biggest area of restriction; the port is
about 3mm dia. way to tiny. I cut mine in the mill
with a .125" endmill centered in the port .125 to
each side, That is to say over all .250" port from o
ring groove to o ring groove. After that, I make a
lead in with a .375 ball nose endmill; this should
just kiss the leading edge of the o ring grooves.
You can open up the port by just drilling. The .22
can be opened up to #16 drill and the .177 to 9/64
then make a lead in with a counter sink. DO NOT GO
BIGGER THE THESE HOLES!!! If you do the head of the
pellet might drop in the port jam and wad up. The
fix, new barrel, or machine a new end and chamber
it…Believe me, no fun…..
Click
for larger pix
Trigger:
Stone the mating surfaces of the sear and trigger, I
use a spring based on a heavy ballpoint pen spring
from a Pilot pen. Oil lightly.
Set the trigger travel now.
Reassemble:
With some exceptions the valve goes in from the cap
side, Oil the o ring with some light oil to help it
slide, make sure the port is aligned with the port
on the tube, and gently tap it home. Try not to go
past the port up the o ring, if you do more than
likely you'll cut the o ring and have to start over.
With the valve home put the screw in and tighten the
valve body use the big flat tip. You want it snug,
All your doing is seating the o ring. So don't get
Jethro on it.
Hammer you can add 20-30 fps by shimming the hammer
with some #10 washer 5/8 dia. This shims up the
hammer spring for more wallop. Here's the catch,
it's a little more difficult to put the breech on.
You have to catch the back pin with the bolt
compress the spring and drop it down on the front
pin all while keeping the breech seal in place. If
the front pin jumps out the front bolt notch and you
don't catch it after you put the breech screw in and
push the bolt forward she'll lock right there. Not
good if you've probed the gun. You can get it off
but it's not healthy for the probe. Also, if you do
these, when charging you have to do it this way, or
it'll blow gas. Open the bolt keep it open, load
your carts, twist the cap down till its good tight,
back the cap off till she hisses, cock the bolt and
fire.
Well that's it hope you enjoy the procedure and Pics.
See you in the funny papers. And always remember
Springer's maybe hot, But Co2 is Cool!!!!
