Originally Posted by
Monster
I was given a rifle where the previous owner had routinely used a stirrup pump, without a moisture trap, to fill it. When I stripped it, to replace the seals, there were clear signs of internal corrosion on some of the parts. Fortunately, the corrosion was not so bad that they could not be cleaned up and the rifle now works fine.
The problem is that the dew point (the temperature at which you get condensation of the water out from the air) is higher for air under pressure than for air at atmospheric pressure. You can probably reduce this effect by filling the gun from a stirrup pump on a cold dry day outside. Cold air contains less moisture, for the same relative humidity, than warm air.
My view is that it is probably OK to just top up a rifle that has been mostly filled from a dive bottle, on an occasional basis, but I wouldn't routinely fill it from empty using a stirrup pump without some form of moisture trap.
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