I have been meaning to post up this article about rust in PCP airtubes and valves...

This fill adapter came out of a Discovery that a fellow sent for a re-seal (it was leaking) and accuracy tune.

I have seen rust in PCP airtubes before, but nothing like this one.

The valve stem was rusted through the zinc plating, and the stainless adapter has residue throughout. The airtube had a film of surface rust the entire length of the tube, with a thicker deposit to one side... I suppose the eide of the gun that was laying down in the case while being stored. Gun was from South Carolina.

It was an easy fix, but this is what can happen if you're not careful about moisture getting into the airtube either through a manual pump without a dry pack or a high pressure pump with insufficient drying capability. This was being filled from a portable air pump (gas powered).

This project was a slightly different one than I am used to. The customer wanted a full shroud on his 2250B with the RJ Riser breech ... but he didn't want any of the Stage V effects.

I made this full shroud with 1" body tubes and Delrin collars. I crowned the barrel flat with a slight target crown. Then I trimmed the front end cap flush with the barrel, also with a slight "target" chamfer.

It looks great and had a nice heavy hang to it.

I was fooling around with a couple of PC77 Crosman Pump pistols, and as I was looking over a valve I noticed there was some flash remaining from a driling/reaming operation at the factory.

I took the valve apart and decide to try a couple of things to make it easier to pump and perhaps increase the power a bit.

I profiled the valve head to offer less shrouding of the valve seat.

I trimmed down the inlet valve to give a bit more internal volume.

The flash in the port was removed and a new port angle reamed with a 1/8" end mill.

I trimmed a bit off the end of the valve body inlet to try to use the air that is trapped between the parachute seal and the valve body tip. Careful here ... too much and the pump arm will flop upon firing. (I think a better way to achieve the same result would be to drill tiny holes fron the sides of the inlet cone through to the inlet hole.

Before assembly, I replaced the valve spring with one from a 2240 and stretched it out a bit. The softer spring makes it easier to "crack" the inlet valve while pumping, but the gun must be "half-cocked" to be pumped.

Results....

Before mods ...

10 pumps, 500 fps

15 pumps, 544 fps

20 pumps, 564 fps

After .... Much easier pumping, and less noisy....

10 pumps, 528 fps

15 pumps, 568 fps

20 pumps, 609 fps

30 pumps, 635 fps

The other PC77 will get a new TKO design flat top pistol ... (zero headspace, with minimal space between valve sealing o-ring and piston o-ring.)