“Shot cycle dynamics in 3 spring-piston airguns”

[Geezer]

https://www.ctcustomairguns.com/hect...airguns-chap-2

One for the techies, tuners and springer enthusiasts.

[Born Again]

Excellent link, my inner geek is going to enjoy that immensely.

[TonyL]

Thank you Mr Geezer. Not sure how, but I nearly missed this. Having a look now.

[TonyL]

Some brilliant detail there and many, many good points and observations to take on board. I'll have to read it through again to get more out of it.

Many of the observations tie in nicely with Jim's superb work. For example, velocity output slowing as friction increases as the piston seal warms and expands. Plus the shoulder acting as an energy store to ping that rifle back, affecting the recoil pattern & deflection and the attitude of the rifle.

However, if I'm reading it right (and those surge accelerations look scary-quick), this study indicates pellet exit to occur in the first rearward recoil phase as opposed to in surge. So that violent surge not as detrimental to accuracy as it could be?

As I say, there's a heck of a lot to absorb and I'll have another look. It'll be great to hear the views of The Lord of The Springs and our esteemed shed tuners too.

Again, thank you for posting, Geezer. A most excellent find.

[TonyL]

I've just had another quick look at that graph incorporating the pellet exit lines.......So, according to these, pellet exit occurs whilst the rifle is still moving backwards. But pellet exit also occurs whilst surge acceleration is quite rampant. So, is the piston actually travelling backwards at this point but the rifle as a whole is still travelling rearwards due to momentum, causing a "delayed reaction effect". I'd actually questioned this some time ago on here, where I thought that there would have to be such a delayed reaction owing to the inertia and momentum of the gun.

All good stuff.

[BTDT]

I've just had another quick look at that graph incorporating the pellet exit lines.......So, according to these, pellet exit occurs whilst the rifle is still moving backwards. But pellet exit also occurs whilst surge acceleration is quite rampant. So, is the piston actually travelling backwards at this point but the rifle as a whole is still travelling rearwards due to momentum, causing a "delayed reaction effect". I'd actually questioned this some time ago on here, where I thought that there would have to be such a delayed reaction owing to the inertia and momentum of the gun.

All good stuff.

The pellet passes over two light gates to record velocity, Tony. The first spike is pellet exit, which occurs during primary recoil when the available piston stroke is 130mm.

[Black Beard]

According to modelling, the piston turns around on a typical airgun (HW80- God's own airgun) when the pellet is about 50mm down the barrel. Pressure peaks just before this. There are lots of factors in this like calibre, pellet weight, cylinder, piston, spring......

At this point the air gun is experiencing a lot of forces and it is still moving backwards (although the piston has stopped). Some of these forces are huge - like 5000N/1000lb- but very short lived.

When the pellet leaves the barrel then the piston has moved back by 7-10mm and is still going backwards at about 5-6 m/s.


BB