just upgraded my leather HW35 to synthetic...

[Shed tuner]

I should say first up, that mine had the small (2.9mm) port. If yours has the larger (3.5mm+) port, this may need sleeving.

I machined a shoulder on the piston face to form the reduced diameter section for the synth seal's shoulder to sit on. Then I machined up an ally disc approx 24.5mm dia 3mm thick to form the "mushroom button" that retains the seal. trimmed off the M8 threaded piston rod to suit, threaded on the mushroom with a bit of loctite, job done. The stroke is extended by 4mm (I could have squeezed 5 before hitting cocking slot issues, but 4 was easier). I grabbed a tatty used Hw80 seal from the parts bin and sized the rear edge down a tad (leaving the front lip untouched).

Before starting, power was bang on 11 FP with leather... with this setup, I had to remove 2 coils to get it legal, back to 11.4. Importantly, it is so much smoother - because it is less snappy - and it has a better air cushion (no doubt also due to the stroke increase). The reduction in preload also means the piston is more cushioned in it's landing. It was quite nice before, but this has transformed it.

Thoroughly recomended if you have a small port (or can sleeve it).

HTH - JB

[TonyL]

Top result and excellent information, JB.

They really are nice, aren't they?

My old "war dog" of a '35, a quite nasty looking thing cosmetically and bought for £30 ten years ago shoots beautifully. It has the Knibbs convertor, so will probably have an even shorter stroke than standard and V-Mach spring, top hat and guide and is very, very smooth. Bet it's not as nice as yours, though, as it still runs the larger diameter TP.

Mick has also posted in the past detailing fitting the later factory piston intended for the synthetic seal. So, for those unable to perform the work involved or having no access to a friendly engineer, fitting the later piston enables the use of the synthetic seal (obviously), increases the stroke (4-5mm I think) and is also lighter.

Love the 35. An old classic design with excellent barrel lock up, superb trigger and excellent balance, especially on opens. Not daft money new and often available at positively bargain prices secondhand.

Day off tomorrow......hoping to get the war dog out!

[jonnyone]

Informative post there shed-tuner. I've long been an advocate of swapping from leather to synthetic (but not in the way some people think)
As Walter eluded to in his airgun book you have to wonder what the Original 45 could have been capable of back in the day had M&G not had a rush of blood to the head and fitted the guns with leather piston heads. As mentioned above with the HW 35 you can pick up the steel converters to swap over but your work here seems even more productive. Like you I've always thought along the lines of reducing spring input after swapping from leather to make the most of the more efficient seal. You've demonstrated it admirably here. I do wonder if this also brings benefits of reduced wear (to a degree) since cocking effort and strain on pivot points is reduced slightly.
I know there are guns that perhaps it's best to stick with the factory leather particularly when needing to keep a collectable gun 100% original, and of course there will always be those who would class you as a heretic for swapping to synthetic. But from my experience it pays dividends in the vast majority of cases.
Again, thanks for the informative post.
Dave

[TonyL]

A few have also used 'O' rings to very good effect.

I have had the absolute pleasure of trying a few thus converted by Mick, T20, and they have all, without exception, shot beautifully.

[deejayuu]

Good read. Thanks for sharing. Which calibre please?

[Shed tuner]

cheers chaps...

It's a .22 E - if you had a .177, this is defo the way to go to get 11+

Incidentally, I see a synth sealed piston on the bay right now - a good drop in replacement (sale is not mine, but I think it may be a chap on this BBS).

The 4-5mm stroke makes for a lot of extra air on a 30mm comp tube, plus the reduced friction and enhanced sealing.