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PostPosted: Mon Jan 27, 2020 9:45 pm 
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Location: Eastern Townships
Voltar1 wrote:
Mirror finish means ALL the lube gets wiped away by the seal. Imo the cylinder works best with a cross hatch finish. Anyways keep us posted on results. Also make changes one at a time or you will be endlessly frustrated if something does not work.


Words of wisdom, thank you Walter!


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PostPosted: Sat Feb 01, 2020 2:01 pm 
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Location: Eastern Townships
Here's an update on my project:

I installed and shaved to size the 5 bronze buttons I made, and I had to make an offset riveting punch. All went well as I planed, finish and fit is as close as it can be to perfect :) . The compression tube is 0.9870'' ID, the buttons are machined to 0.9855'', this gives a very nice ''slip-fit'', even before adding lubricant. I still have to clean and burnish with WS2 powder the piston and tube, and re-assemble the parts for testing, but I'm confident this mod will yield good results.

First set of pics:


Attachments:
Bronze_buttons_2.JPG
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Bronze_buttons_3.JPG
Bronze_buttons_3.JPG [ 33.09 KiB | Viewed 129 times ]
Offset_punch.JPG
Offset_punch.JPG [ 83.76 KiB | Viewed 129 times ]


Last edited by airmec on Sat Feb 01, 2020 2:04 pm, edited 1 time in total.
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PostPosted: Sat Feb 01, 2020 2:03 pm 
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Location: Eastern Townships
Second set of pics:


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Bronze_buttons_4.JPG
Bronze_buttons_4.JPG [ 28.79 KiB | Viewed 129 times ]
Bronze_buttons_5.JPG
Bronze_buttons_5.JPG [ 25.91 KiB | Viewed 129 times ]
Bronze_buttons_installed.JPG
Bronze_buttons_installed.JPG [ 85.06 KiB | Viewed 129 times ]
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PostPosted: Sat Feb 01, 2020 8:13 pm 
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Joined: Mon May 26, 2014 1:08 am
Posts: 493
Location: Thunder Bay
Beautiful work!

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12 springers and a couple of pumpers.
2 lathes and lots of scrap metal.

Too soon old too late smart.


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PostPosted: Sat Feb 01, 2020 8:39 pm 
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looking good... 8)

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"A candle loses nothing by lighting another candle"

Image


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PostPosted: Sat Feb 01, 2020 11:12 pm 
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Location: Eastern Townships
Thanks guys :)

I've chronied the rifle with the new piston today. The spring is at the stock installed height, no shimming. Just as a reminder, my last chrony test gave 421 fps (5.65 fpe) with JSB Jumbo Express 14.35 gr. pellets, with the stock piston. With the custom shorter piston, same pellets and everything else the same, the chrony showed a 434 fps reading, for exactly 6 fpe, an increase of 3%. I'm quite happy with these results, I think it roughly relates to the swept volume augmentation, or a bit better :) . Also I saw on another forum that I may expect a slight velocity increase when the seal ''settle in'', not wear in, the compression chamber walls are smooth. Teflon seals do ''crush'' with use and fill the space better with time (I hope!). Now I need to finish that fitted spring guide...

Forgot to add: Cocking is ultra smooth with the bronze buttons, and they don't rattle when the rifle is fired 8)


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PostPosted: Sun Feb 02, 2020 9:19 am 
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Joined: Fri Jan 22, 2010 1:17 pm
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Location: Kingston, ON
That's the most modded B18/19 piston I have ever seen.
It would take some tuning to match spring properties to the increased swept volume, but we will wait to see if your results over the chrony, and on paper show the mods have improved it or just changed it.
And your gut feelings about the shot cycle. :drinkers:

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PostPosted: Sun Feb 02, 2020 5:15 pm 
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Location: Eastern Townships
Dukemeister wrote:
That's the most modded B18/19 piston I have ever seen.
It would take some tuning to match spring properties to the increased swept volume, but we will wait to see if your results over the chrony, and on paper show the mods have improved it or just changed it.
And your gut feelings about the shot cycle. :drinkers:


And I didn't even installed a plastic sheath inside :wink:

I've finished and installed the spring guide, and I'll post updates on the project in my other thread: topic84819.html

First gut feeling is easy to express: wooooooow, smoooooth and quiet :lol:


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