just upgraded my leather HW35 to synthetic...

[Shed tuner]

No problem!
I have done the conversion, and machined down the front. The pin that goes through the piston body/front/stem was the determining point for me, didnt want to weaken the surrounding material too much, and left a conservative amount of piston ahead of the pin. Ended up with a 69mm stroke, and had to remove som material at the rear of the piston slot for cocking arm clearance.

Sounds about right

More importantly, are you happy with how it shoots now ?

[evert]

Sounds about right

More importantly, are you happy with how it shoots now ?

Not all there yet compared to my modern HW35, but velocity and recoil improved over the previous conversion where I just cut down the threaded stud a bit and mounted a synthetic seal. I dont have any velocity numbers in my head these days, work stress takes care of that...

The gun has an original spring, with a shrink tube over the original steel guide, and a heavy steel tophat.
I have a Maccari/ARH replacement which has a thinner wire and more preload. This spring works well in my modern gun, so trying that will be next.

I did a "breech void filling" with JB weld on the gun a while back, but didnt get any great effects of that. Looking down the tube I dont see any JB weld around the breech pug back end, so I'm thinking the process works better with a thinner product lice loctite that seeps into the voids with capillary effect.

[Shed tuner]

I'd get rid of the heavy steel TH too - they really don't help as the piston is already on the heavy side, and the stroke is short... unless you have a compeltely unsuitable spring fitted...

[TonyL]

Not all there yet compared to my modern HW35, but velocity and recoil improved over the previous conversion where I just cut down the threaded stud a bit and mounted a synthetic seal. I dont have any velocity numbers in my head these days, work stress takes care of that...

The gun has an original spring, with a shrink tube over the original steel guide, and a heavy steel tophat.
I have a Maccari/ARH replacement which has a thinner wire and more preload. This spring works well in my modern gun, so trying that will be next.

I did a "breech void filling" with JB weld on the gun a while back, but didnt get any great effects of that. Looking down the tube I dont see any JB weld around the breech pug back end, so I'm thinking the process works better with a thinner product lice loctite that seeps into the voids with capillary effect.

When I did mine last year, evert, I used the JB Weld heavy duty thread lock. Think it's called Perma Weld. Seemed to do the trick........although I do wish I'd done some steps in isolation rather than all at once.......sealed the breech void, fitted later piston and new seal (courtesy of Mick, T20), replacing the old piston that had a Knibbs converter and seal fitted. We now know that that conversion robs precious stroke and the piston seal had gone ridiculously tight so must have been robbing power. Hence I'm not sure where the bulk of the power gain came from.........177 and up from 6.5ft.lbs to 11.2.

Edit :- The JB Weld product I used was Perma-Lock.