HW/Weihrauch 22mm tune on a HW97

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HashBrown123

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Dec 19, 2021
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UK, United Kingdom
Hi all,

I've been developing a 22mm tune on my HW97, .177 rifle. The piston is skirtless, 130g with tophat, o-ring sealing and on a TX200 mk3 spring and latch rod.

I'm quite happy with it but recently a leaky compression tube has had me questioning things and I thought it would be interesting to get some more thoughts on a solution.

Initially the rifle was set up to shoot 8.44 exacts @ 760fps, I had issues with the comp tube leaking originally. I think I had a void in the compression tube sleeve, I fixed this by sealing the end with retaining compound.

Eventually after shooting a tin of pellets through it again I thought "bugger me, this rifle is shooting really well". The recoil was pleasant, the gun was very easy to shoot, I couldn't really feel any hold sensitivity and no loss of sight picture on recoil. Very happy moment after a couple of weeks of amateur hour engineering in my garage.

However when I chrono'd the gun I found it was only shooting at 700fps, I suspected the leak was back and I was right. Upon getting home and re-sealing the compression tube the gun was doing 760fps again.

I spent a couple of hours shooting the gun today and it was not as nice. It feels like I'm getting piston bounce, the sight image is easily lost and is much more difficult to shoot compared to before.

To me this is strange as nothing else changed, it's the same spring, piston, o-ring, pre-load... Everything. The total energy released when I fire cannot change but the feel of the rifle did.

I will be making another compression tube with a new sleeve, one that will not leak. But I am hesitant to do this until I have this one shooting well...

With a leaking compression tube I am thinking that the pressure build up in the compression tube will be less, therefore this reduced pressure will result in less piston bounce.

Can I achieve the reduced piston bounce by opening up the transfer port? Currently I think the transfer port is around 3.2mm. I'm thinking 3.6 might be worth a try...

I think I'm going to do this anyway and I can always turn up a brass tube to reduce it again if I go too far but I'm just wanting to bounce ideas off other people before I have a go later.

Cheers
 
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22mm? "Skirtless"? You've done so many design changes my head spins. I don't know where to start. Maybe some pictures might be helpful.

FWIW the lighter the piston the more likely it is to bounce. Piston alignment is critical for consistent sealing. Without a skirt and lightweight I would expect poor sealing and piston bounce. Transfer port sizes are something I've never messed with. I don't trust my luck to mess with original design parameters. Since you've gone this far, opening the transfer port will likely reduce piston bounce but may also reduce velocity from lost volume.

I admire your ambition.
 
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My man, skirtless pistons are not new. Neither are 22mm pistons.

The piston is kept square via the spring guide. The spring guide is reamed to 0.002" larger than the latch rod. Squareness isn't an issue. It will be kept more square than the factory piston.

My comp tube seems to be a problem but I will make another when I settle on final specs.

PXL_20231118_134701094.jpg
 
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After reading your first post a second time. I was wondering if the gun might have been dieseling when the recoil became noticeable after a few hours of use. That would increase the energy and recoil. You'd surely pick up the the dieseling with the chrono or extreme cases with your nose.

Out of curiosity, what are you using as a seal? I know you said o ring but round or square profile? and for lubricant? Was the spring set before your initial pleasent run?
 
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A.G.R said:
I suspect this to be TL…. ?
nice work ..

springs can set and change the control of recoil as you know.. o rings settle in. It’s why I left the O-ring game for goot … 😉
Click to expand...
I'm not TL, just an idiot in a shed with a lathe.

Mycapt65 said:
After reading your first post a second time. I was wondering if the gun might have been dieseling when the recoil became noticeable after a few hours of use. That would increase the energy and recoil. You'd surely pick up the the dieseling with the chrono or extreme cases with your nose.
Click to expand...
I used a teflon based lube that does not diesel.

I really think it's down to piston bounce that I hope to eliminate.

Mycapt65 said:
Out of curiosity, what are you using as a seal? I know you said o ring but round or square profile? and for lubricant? Was the spring set before your initial pleasent run?
Click to expand...
Standard round shore 70 o-ring. 18mm x 2mm
 
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Mycapt65 said:
Alright keep us posted. I'm curious to see how you make out. Perhaps try more preload? If the spring took a set you might have lost preload and gained bounce? Just a thought.
Click to expand...
I'm on about 20mm of preload at the moment, I will be trying to add more though.

I do suspect the transfer port though. I think I will come up with a way to swap out transfer ports, possibly bore out the current comp tube and thread the transferport and make some brass inserts.
 
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The 97 sliding compression tube lends itself to threaded TP inserts more than a standard Weihrauch break barrel. I've often thought of playing with TPs but shied away from it.

The guns I've considered doing it the most were 177 R1s. They're very violent and I thought there's enough power to spare it'd be worth it to decrease the piston bounce from the typically high 177 start pressure.
 
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I opened the transferport up today, from 3.3mm to 3.8mm.

The bounce situation was better, but it was still there.

I tried a bit more preload, added 5mm. Things felt better again, but it's still there.

I think I'll be making a new top hat in brass for a bit of added weight or swap the 5mm of preload with a 5mm thick steel washer on the piston. I'll add 10g of weight and see what happens, I expect further gains again.
 
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HashBrown123 said:
I opened the transferport up today, from 3.3mm to 3.8mm.

The bounce situation was better, but it was still there.

I tried a bit more preload, added 5mm. Things felt better again, but it's still there.

I think I'll be making a new top hat in brass for a bit of added weight or swap the 5mm of preload with a 5mm thick steel washer on the piston. I'll add 10g of weight and see what happens, I expect further gains again.
Click to expand...
Did you solved bouncing adding additional weight?
 
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