CO2 storage in Non AF guns

Found originally posted on yellowforum.com

Here Is What Tim McMurry Says About CO2 Air Guns and Storage:

Early Crosman Bulk Fill guns are often found in working condition even
though the guns are over 50 years old. They used great materials for the
seals that would last for decades. In today’s world little gets the same
treatment. The board rooms won’t have any part of that and the K-Mart
buyers dictate the digit. So what we get we deserve. Guns that last 5000
shots and shouldn’t be left charged or they will barely get through the
warranty period.
So nowadays the guns have very soft seals. The soft seal is always going
to be an easier part to make function. In the old guns the seal wasn’t
compliant enough to tolerate much in the way of an irregular valve seat
be it dented, scratched or poorly aligned. The hard seal valve needs to
have nearly perfect valve stem to valve body alignment and can be
problematic if not left charged with CO2 to aid in the task of holding
the valve shut. Hard seals are not going to over compress or soak up CO2
because they are of a standard that did not fail when charged for
extended periods. I could name materials but suffice it to say there are
no currently made American CO2 guns that can be left fully charged up
without shortening the guns useful life and costing you power in the
long run.
Same goes for soft seal pump guns. The best approach is to eliminate the
possibility of valve seal over compression by leaving a few pumps in the
gun rather than max. Some guns are affected more than others but to
leave a pumper fully charged is a mistake and will cost you power. They
will not release as many pumps as before once subjected to a full charge
for extended periods. What happens is you think all the air came out and
you pump it fully again but this time it actually has one more pump than
before because it retained one and it is starting to build up residual.
If your not aware of this situation developing you can in a very few
shots severely over pump your gun. Always check with each different type
of ammo how many pumps the gun will physically clear and don’t exceed
that.
Modern CO2 guns basically seal on a end or face seal that is also soft.
The seal is shaped like a donut and if you over tighten your CO2 cap you
will close the hole in the donut down on the piercing pin and restrict
its travel and you will lose power. Too tight is when the cap can be
loosened and it doesn’t start to seep. I loosen the caps till I hear a
faint hiss and retighten slightly. There is no profit in tightening the
cap to the max. It will cost you power. The other thing that often
happens is when you go to remove the CO2 cartridge from a gun that has
had the cap over tightened the seal comes out with the cartridge
requiring a valve removal for a new face seal. This advice relates to
Benj/Sher models F, G397, EB, etc. and to Crosman 2250, 2240, & 2260. In
many other models the over tightening of the cap can effectively cause
the gun to pierce prior to sealing and gush all the CO2 out. On models
with a pierce when cap tightens system like the SSP250 & 262, or the CO2
in the grip type like the 357, Auto AIR II, 1008, C40, etc. this problem
is really common. Sometimes these guns take a minute to seal completely
but don’t be tempted to tighten the CO2 screw as this will usually make
no difference and will cause other problems. Once the cap has been
tightened down enough to fully pierce the gun I always back of the
tension till I hear a slight hiss and I retighten slightly till the
hissing stops. This is the best way to get the most from a modern gun.
Don’t reef on the cartridge and when your done shooting put it away MT
with no cartridge in the system. On guns which hold the grip to the
cartridge you can leave the MT cartridge in the gun as long as it is
degassed and slacked off. All Umarex guns can benefit from this caution
as well.
One other reason for not leaving any of these guns charged with CO2 is
that the orings used are going to allow CO2 to pass through them. It
takes a 90 durometer oring to contain CO2 fully for long periods. A 70
durometer(softer) oring will pass gas. The seals molecular structure is
loose enough to allow the CO2 gas to pass through the oring. This will
in the long run degrade the oring and it can literally cause it to burst
from the inside when the pressure is relieved and the liquid CO2
contained in the oring at time of decompression expands into gas state
and ruptures the oring. The Crosmans of the 60’s and early 70’s used 90
durometer orings in the pressure vessel so these guns can be charged and
left that way. Models that pierced the CO2 cartridges against a end
seal/piercing pin should not be left charged.
S&W 78G and 79G are the first guns I remember telling folks to leave MT.
The main seal on that gun is far too soft to be left charged for long
periods as the sharp seat easily over compresses the seal and can lead
to terminal gutlessness as well as substandard 70 durometer seal
failure.
The MKI & MKII can be left charged but on any CO2 gun that is left
charged you must be certain to avoid the gun seeing higher than normal
temperatures or the seals can suffer. So even when the gun does have the
ability to be left charged it is not a great idea to have the gun
sunbathing. For the best consistency the CO2 systems temperature should
be controlled within the tightest range possible and temperature
extremes should be avoided. MKI LD’s have very large & sharp valve seats
so even though we use 90 durometer I recommend the LD be shot down to a
lower pressure when stored to avoid any possibility of seal over
compression and/or power loss.