Taming a HW99.......

[clipper]

I admit defeat..... HW99 shaking scopes loose! .177, have already fitted a spring guide to get rid of the twang, but it would shake loose the sportsmatch mounts that came with it, and during today's range session has done the same to BKL mounts that were done up as tight as I'll dare before I'd risk stripping threads

It's running just over 11ft/lb with 8.4gr pellets, I had planned to leave it a while for the standard (I got the rifle secondhand but from its condition has seen little or no use) spring to settle, but think time has come to shorten or close up a few coils

Any pointers for how much to start with? Only using it for tin and paper so will happily go down to 10ft/lb

[eyebull]

Have you had it apart yet?

[clipper]

Only to fit Tinbum top hat and spring guide - this didn't change unsprung length or preload (there was a thick 4/5mm power washer at piston end of spring from factory)

[TonyL]

Firstly I'd be checking both the breech and piston seals.

Once satisfied that they're okay, reducing the preload (combined with properly finishing and polishing the spring ends) may bear fruit. If not, a softer spring (like the TX200 Mark 3 item) might well improve matters. I have a Wonkydonky kit in one of my 99s and it's very nice.

[bighit]

I shot a .177 HW99s that had another tuners kit in at the weekend. It felt a little harsh but it was the first .177 I had shot in almost 20 years.

It was not a TBT kit 😉

[evert]

11 fpe on 8,4grs is a bit more than what I like in the HW50/99.
Mine is running on Maccaris HW50/99 spring plus his SGS seal.
Nice quick shotcycle at 10,5 fpe, and the SGS seal softens it up a bit compared to the original seal.

[maximus]

Firstly I'd be checking both the breech and piston seals.

Once satisfied that they're okay, reducing the preload (combined with properly finishing and polishing the spring ends) may bear fruit. If not, a softer spring (like the TX200 Mark 3 item) might well improve matters. I have a Wonkydonky kit in one of my 99s and it's very nice.

Do this, if it was second hand who knows whats been done. Check no one has reamed out the t.p. to some huge size, could also of had an inappropriate spring fitted too i guess. It sounds like its particularly bad and not running at a ridiculous power really.

[tinbum]

As mentioned above, simply reducing power to sub 10.5 makes the .177 a different gun!

[keithy]

I admit defeat..... HW99 shaking scopes loose! .177, have already fitted a spring guide to get rid of the twang, but it would shake loose the sportsmatch mounts that came with it, and during today's range session has done the same to BKL mounts that were done up as tight as I'll dare before I'd risk stripping threads

It's running just over 11ft/lb with 8.4gr pellets, I had planned to leave it a while for the standard (I got the rifle secondhand but from its condition has seen little or no use) spring to settle, but think time has come to shorten or close up a few coils

Any pointers for how much to start with? Only using it for tin and paper so will happily go down to 10ft/lb

Use the recoil screw on the rear scope mount. If it's not in the mount buy the correct size grub screw.