Webley Hawk MkIII

[harry mac]

Quite right harry mac
And it did give me a spare piston and cylinder to try O rings out on (19mm Id x 2.5mm works Guy ).

I'd be interested to hear the results of the o-ring experiment. Does it increase the power at all?
I've got a spare MKIII which is there solely to act as a donor rifle for spare parts should the others need them. It exhibits nearly every fault that the Hawks are renowned for.

[T 20]

I'd be interested to hear the results of the o-ring experiment. Does it increase the power at all?
I've got a spare MKIII which is there solely to act as a donor rifle for spare parts should the others need them. It exhibits nearly every fault that the Hawks are renowned for.

Hi Harry

I've not tried the O rings in a working gun yet as I need to get a few parts from John Knibbs' before I start.
The original PTFE rings never seemed to work very well and when they did they didn't last very long. On hydraulic applications a PTFE ring like that would have a rubber ring under it to force it outwards onto the cylinder wall to create a good seal. The Hawk and Osprey rings just tend to sit on the piston with no inbuilt spring to keep them in contact with the cylinder wall.

The 19mm Id x 2.5mm O rings when fitted give an overall crush of 0.028" with 0.014" crush per side. This is a little bit less than I had hoped for but should still work well enough in a small cylinder (24.8mm). When I eventually get around to sorting my Hawk I'll be fitting two O rings to the piston and the gap between them will be used as a reservoir of MS50, this is an old John Bowkett trick I'd like to try and the Hawk lends its self to it rather well.

I'm hoping for a small increase in power with this mod as the piston will have a more positive seal using O rings, so all the air in the cylinder should go up the pipe instead of some blowing past the PTFE rings. I always find O ring seals give a really good shot to shot consistancy as well, so using O rings on the piston should be a win -win situation.


All the best Mick

[westy1946]

Hi, I have just aquired a MkII Hawk and it like Harrymac has described in post 3 the end cap pin has distorted the piston tube and the trigger block has fractured and broke off, I was able to set the trigger and chrono it with Bisley Magnums .177 and recorded 10.78ft/lbs, obviously uprated spring at some time. There was no safety. I wonder if it was safer using without than with one? All the recoil and stress has created a split in the stock(repaired) and this pressure has travelled back to the trigger guard pin and transfered leverage to the trigger block (chain reaction) causing metal fatigue and snapping welds. I was hopeing to resurect this gun but it is looking rather doubtfull now.

[harry mac]

Hi, I have just aquired a MkII Hawk and it like Harrymac has described in post 3 the end cap pin has distorted the piston tube and the trigger block has fractured and broke off, I was able to set the trigger and chrono it with Bisley Magnums .177 and recorded 10.78ft/lbs, obviously uprated spring at some time. There was no safety. I wonder if it was safer using without than with one? All the recoil and stress has created a split in the stock(repaired) and this pressure has travelled back to the trigger guard pin and transfered leverage to the trigger block (chain reaction) causing metal fatigue and snapping welds. I was hopeing to resurect this gun but it is looking rather doubtfull now.

What shape stock is it in Westy? Early or late MkII?