Air Gun Home :: View topic

kanyon · Silver Status Member

Hello.
Got bored the other day so I pulled one of my B11 apart just to see what was in it "not much as it turns out"
Now that its in bits I may as well have a play with it.
Got 10 of them so if I end up trashing it well its not a issue.
So I have a few questions...

Q1 = its a .22 cal 5.5mm bore but the air hole from the piston chamber
is only 3mm CAN this be made larger or dose it need a restriction as this point to act as a cushion for the piston?

Q2 = when the spring is compressed there is a avarage of 1.2mm between spring coils which means the spring can be compressed another 18mm before it becomes coil bound so i want to put a 10mm spacer in
BUT what end should the spacer go puting it on the piston end it will add weight to the piston. What end should it be??

If this gun is anything to go by... You should NEED to pull chinisse air guns apart and clean them it was full of thick grease full of metal fillings & grinding stone particals felt like very fine grinding past NOT GOOD.

broommaster2000 · Moderator

If I recall correctly, the spacers should be placed over the spring guide, allthough it seems to be on this rifle that you got a spring guide on the wrong side. They usually are located where the spring meets the trigger group.

Polishing the whole compression chamber a bit will probably help. Maybe you can fit a Gamo spring, if it's not to costly.

And cleaning it, and relubing it off course. I'm not sure what kind of stuff is best to use to clean the insides of a gun. I just use huge wads of toilet paper on my slavia, which means one or two hours of work, and some leftovers that you will try to remove but almost isn't worth it. (That's a "don't")

cw · Banned

Q1:

Tuning the transfer port to a larger size can be tricky at best.
It must be enlarged in very small increments.
If you go too big, you run the risk of making the gun a piston seal
eater (even with heavy pellets).

Stock, OEM transfer ports are tuned small on purpose to provide
enough resistance to the air flow to cushion the piston enough
in case light pellets are used.

When enlarging a transfer port, usually the port is tuned to a specific
pellet weight. I have tuned the transfer port in several Patriots to 21
grn Kodiaks. They usually gain 3-4 fpe doing this. Except now, lighter
pellets cannot be shot in them. When lighter pellets (such as 18 grn
Cro-Mags) are shot through these guns it is quite harsh and damaging
to the piston seal because the light pellet does not provide enough
resistance to cushion the seal and keep it from slamming
into the end of the comprssion chamber at the end of it's stroke
and the enlarged transfer port does not provide enough resistance.
So when shot, the gun will gradually round the edge of the piston seal
until it is too rounded to seal properly.

Q2:It is best in most cases to not add any weight to the piston
assembly. Add the spacers to the stationary end of the spring.
Usually the only limitation that you will run into is coil bind, where
the spring coils are compressed so far as to be touching.

cw · Banned

I might add that instead of adding a spacer, you might want to
try using a thust washer stack for spacing. That way you will reduce or eliminate any torque or hold sensitvity.

http://www.airgunhome.com/agforum/viewtopic.php?t=1341

kanyon · Silver Status Member

Thanks CW your reply clears things up nicely. I think instead of opening the port up I mite play with the inlet end try to improve the flow characteristic's.

Thanks K

cw · Banned

Be careful that you don't increase the headspace (volume
left in the compression chamber when the piston is at the
end of it's stroke) or you will loose power. A lot of
people do this by rounding the inside edge of the transfer port
to achieve a better flow.
Even increasing it a little can be disastrous.