Jim's piston seal article in AGW...

[greenwayjames]

Some time ago I saw a photo of one of Gerald Cardews W&S Hawks that he used for development work. It was one he had been using to test anti-bounce piston devices. It still worked fine. The Hawk is owned by John Bowkett. As many know I am involved in his facebook fanpage. I will see if I can get permission to put a pic of it either here or over there if anyone is interested?

[hmangphilly]

I know there's no 'one size fits all' answer but where abouts in the stroke would you expect a 25 mm piston to bounce ? ....1-2 mm from the end ? more ?

[davep]

I know there's no 'one size fits all' answer but where abouts in the stroke would you expect a 25 mm piston to bounce ? ....1-2 mm from the end ? more ?

Cardew in Trigger to Target suggests 0.1 inch so about 2.5mm. I think he was measuring pressure in the cylinder so probably fairly accurate

[Loki_79]

I know there's no 'one size fits all' answer but where abouts in the stroke would you expect a 25 mm piston to bounce ? ....1-2 mm from the end ? more ?

From my computer model, I would say anywhere between about 0.1mm and 0.5mm.

edit: I should say that most of the variation depends on the resistance of the pellet, a completely blocked barrel with a 3mm transfer port and minimal other lost volume I get something like 1mm.

[hmangphilly]

so depending on the fit of the pellet ,
we've got , let's say an 85mm long x 25mm dia column of air plus tp /etc, compressed into 0.1-0.5mm x 25mm dia plus tp/.?

[TonyL]

From my computer model, I would say anywhere between about 0.1mm and 0.5mm.

edit: I should say that most of the variation depends on the resistance of the pellet, a completely blocked barrel with a 3mm transfer port and minimal other lost volume I get something like 1mm.

Blimey! I thought that it was sooner than that, more like 5mm or so, but I can't remember if I've read something in Jim's articles or elsewhere. I, of course, could me miles off (I often am!).

Now, some of us have mused for years about this and wanting to uncover some more of the springer's innermost secrets, but we really need a see-through cylinder and a camera with 1000 frames per second capability. This would reveal SO much......

[hmangphilly]

Blimey! I thought that it was sooner than that, more like 5mm or so, but I can't remember if I've read something in Jim's articles or elsewhere. I, of course, could me miles off (I often am!).

Now, some of us have mused for years about this and wanting to uncover some more of the springer's innermost secrets, but we really need a see-through cylinder and a camera with 1000 frames per second capability. This would reveal SO much......

thats a brilliant idea

but you could get a good idea of whats going on by filming the piston through the cocking slot .
suitable graduations marked on the piston would work .

trouble is them pukka high speed cameras are ££££££££££££££££££££££

[TonyL]

thats a brilliant idea

but you could get a good idea of whats going on by filming the piston through the cocking slot .
suitable graduations marked on the piston would work .

trouble is them pukka high speed cameras are ££££££££££££££££££££££

Well, bugger me with the blunt end of a bus!!

A few of us had previously debated about likely materials for the see-through cylinder and its expected poor longevity.

But there's the answer, crystal clear, in your post....nice one!

As you say, some markings on the piston (and also on the cylinder) at the cocking slot. I know those high speed cameras cost fortunes, but if only this could happen.....I wonder if a laboratory at a university would be up for some experiments? We could have a few rifles readied, with different bore, stroke, pistons, TP set up etc. if the equipment worked, just one or two filmings per gun would do.

[Rickenbacker]

Blimey! I thought that it was sooner than that, more like 5mm or so, but I can't remember if I've read something in Jim's articles or elsewhere. I, of course, could me miles off (I often am!).

Maybe you're thinking of how much it bounces rather than when, Tone?

The question of 'how much', 5 - 10mm is it?

[TonyL]

Maybe you're thinking of how much it bounces rather than when, Tone?

The question of 'how much', 5 - 10mm is it?

Mmm....to be fair, lovely Phil, I think I was maybe referring to a figure I have in my head of 95% of the stroke from some of Jim's earlier articles.....But the 95% possibly refers to (approximately) pellet release point and not onset of piston bounce?

I did say that I'm very often wrong!

[Shed tuner]

from various models, experiments and other and sources, headspace at the point of bounce can be anwhere from 0.5mm for the most extreme, short stroke beasts to around 10mm. for a well set up gun (for 12 FP), I'd go with around 1.5-2mm.

The amount of bounce can be anything from 10 to 20+mm

TopDog on here (who we had the pleasure of meeting at the bash) has measured piston displacement directly using a potentiometer arrangement, to get real time piston position graphs. Very interesting

[greenwayjames]

Measuring piston position was recorded in one of Gerald Cardews W&S Hawks that nobody was interested in seeing a picture of.
My previous post.
Some time ago I saw a photo of one of Gerald Cardews W&S Hawks that he used for development work. It was one he had been using to test anti-bounce piston devices. It still worked fine. The Hawk is owned by John Bowkett. As many know I am involved in his facebook fanpage. I will see if I can get permission to put a pic of it either here or over there if anyone is interested?
The pictures I saw showed a long thin rod that appeared through the rear of the antibounce device that was welded to the rear of the cylinder. I know that Bowkett has all of the masters masters plus a load of paperwork and photos concerning his experiments. I wonder if the results of his experimenting are amongst them? I am probably talking to myself again. San fairyanne as the frog eaters say

[bmp01]

Measuring piston position was recorded in one of Gerald Cardews W&S Hawks that nobody was interested in seeing a picture of

Ok. Please can you post a picture of the Gerald Cardrew's gun used for measuring piston position.

I'm sure the techniques used were the best of the day, might still be very useful. Any insight as to how the measured data is used would also be beneficial.

BMP01