Taking weight off a hw97 piston

[ElmerFudd.177]

How would any of you tuners out there take some weight out of the hw97 piston?

The start weight is around 265 grams if i remember, what weight should i aim for?

Im going to be fitting a tinbum short stroke and drop in kit, deburr and polish all internals fit a spring sleeve,

Any other suggestions welcomed...

[ElmerFudd.177]

Done some reading through some old threads and it appears that the magic number is between 220 and 250 grams but have to make the transfer port larger to around 3.9mm and taper inside the compression tube to allow easier flow for a lighter piston.

If im wrong can someone tell me as im planning this for next week please.

Thanks

[buttloaves]

Drill some holes in it..

[Shed tuner]

Drill some holes in it..

yeah, and just skim a bit off the body. play with the TP last to fine tune, but yes, will probably need opening to at least 3.5 (assume it's a 26mm). In terms of target weight 210-220g should be perfect for a 26mm.

[ElmerFudd.177]

Yes it is 26mm...

Do the holes have to be opposite to balance the piston?
And which size drill bit to use? (Obviously smaller drill bit = more holes)

Thank you

[buttloaves]

Wonder if the center of gravity has any effect, are pistons better front heavy or skirt heavy, i would think front heavy is best but i could be wrong..

[ElmerFudd.177]

I cant work you out "buttloaves".

Are you trying to say i have to work it out for myself?

Just thought some might like to share abit of knowledge to save a poor man ruining an air rifle.

[RobF]

Wonder if the center of gravity has any effect, are pistons better front heavy or skirt heavy, i would think front heavy is best but i could be wrong..

Makes no difference. It's always supported by the same points. The hw 97 piston doesn't rotate.

[Nessmuk]

What's the thinking behind taking weight off the piston? Does it accelerate faster reducing the firing cycle time, or maybe less recoil?

I really must read my copy of from trigger to target one day!

[Mark A]

Drill some holes in it is a lot harder than it sounds. I managed to destroy a deWalt cobalt 6mm drill bit just making 3 half holes in a Cometa piston. I would imagine a Weihrauch piston is even harder.

The piston in my Webley Tomahawk seems way too heavy, think i might end up sending it to someone who can machine some weight off it rather than trying myself as its not like there are many spare parts about for these guns now .

[Shed tuner]

If it's hard..

soften the area (not the rear of the skirt) with a blowtorch
centre punch
drill initial hole with centre drill
drill out to req'd size
re-harden if you wish

[TonyL]

What's the thinking behind taking weight off the piston? Does it accelerate faster reducing the firing cycle time, or maybe less recoil?

I really must read my copy of from trigger to target one day!

Yes, generally, a lighter piston will accelerate faster, slightly reducing the "action time" and slightly reducing recoil. BUT, if not properly set up (spring, transfer port size etc), reducing piston weight could result in more piston bounce. These days, we know this as "surge" and it's the forward snap of the springer, which is more detrimental to hold sensitivity.

It's all a question of balance...

I haven't looked through "the book" in ages. An excellent work, especially for its day, but these days surpassed by the briliant work by Jim Tyler and the sadly missed, late Mike Wright.

[TonyL]

Drill some holes in it is a lot harder than it sounds.

.......Is what I believe to be the case with many pistons. With my lack of proper workshop and equipment, it's something that, personally, I'd be getting a machinist to do for me.

[TonyL]

According to Bruce Gill's excellent thread in the Useful / Tips section up above, the 26mm piston weighs 30grams more than a 25mm '77 piston. And the 25s are very, very sweet.

To further confound, Mr Bowkett, I seem to remember, went for a heavier piston????

I wonder if, by simply experimenting with different spring charcteristics, the desired result could be achieved?

Or, if one was desperate to modify, I think the swept volume of a 26 is 4cc more than its smaller pistoned brother. How about a small stroke reduction, giving the same swept volume, by way of a clip-on head? Always easy to revert to standard, also, if you later wanted.

[buttloaves]

According to Bruce Gill's excellent thread in the Useful / Tips section up above, the 26mm piston weighs 30grams more than a 25mm '77 piston. And the 25s are very, very sweet.

To further confound, Mr Bowkett, I seem to remember, went for a heavier piston????

I wonder if, by simply experimenting with different spring charcteristics, the desired result could be achieved?

Or, if one was desperate to modify, I think the swept volume of a 26 is 4cc more than its smaller pistoned brother. How about a small stroke reduction, giving the same swept volume, by way of a clip-on head? Always easy to revert to standard, also, if you later wanted.

Is surface area of the piston face a factor, less force pushing back on the smaller piston.
Is it possible to sleeve down the comp tube to accept a smaller piston?