Hold sensitivity.. Jim's AGW article...

[Shed tuner]

Interesting read Jim, as always The vibration graphs were especially interesting....

Quick rewind.. Whilst I'm sure plenty of folks might have considered that hold sensitivity was very much a function of stroke length, as you I'm sure have more conversation than I about such things with a far wider range of people (I live in a cave), personally I had always thought that hold sensitivity was more a function of piston bounce and it's timing (relative to pellet exit).

Obvious example is an export spec long stroke throttled back to 12 FP with a weedy spring; lots of piston bounce. Shorten the stroke back to std 12 FP specs, less hold sensitivity, stronger spring job done

But both this and the vibration theory come back to the same, pleasingly simple hypothesis.. that what you ideally want is for the pellet to be exiting the muzzle when the muzzle itself is not subject to much movement... now whether that movement is related to rifle displacement or the more subtle affect of vibrations (presumably themselves due to aggressive piston bounce - which would certainly explain why some very light pistons can be hold sensitive without piston inertia to calm things down) is a more interesting question. Am going to dig out some of Jamie accelerometer graphs in a sec and see what can be deduced...

[Shed tuner]

See here for my 24mm HW80



Also the 22mm TX



In both cases the velocity is (near) constant, with low acceleration, at the time of pellet exit (the green dotted line)

[TonyL]

Lovely stuff.

I haven't managed to read the article yet but, as ever, looking forward to it.

Cheers for sharing those graphs and information, Jon.

[TonyL]

What do the "Y" and "Z" lines correspond to, Mr B?

[Shed tuner]

What do the "Y" and "Z" lines correspond to, Mr B?

X= along
Y = up and down
Z = side to side

See the "Y" muzzle flip in the last graph...

[BTDT]

Glad you enjoyed the article, Jon.

With hold sensitivity, as with so many aspects of the springer shot cycle, we tend to hamper ourselves by seeking a single reason for any phenomenon, when there could be more than one cause, depending on a variety of factors, including how the rifle is set up, and how it is used. People find a simple relationship between recoil displacement and hold sensitivity appealing, because it’s easily understood, and we can alter recoil displacement at will. It is equally likely that the cause is recoil or surge acceleration, vibrations at some point in the recoil cycle, or a combination of these plus displacements. We just don’t yet know.

Jamie’s graphs are based on acceleration measurements. To find velocity, we have to integrate the acceleration data, averaging each pair of figures, which can mask large differences between adjacent figures, smoothing out vibrations. If you note the fluctuations in Jamie’s x axis accelerometer graph, you’ll see they’ve largely disappeared from the integrated velocity graph. Sorry, Jon, but when the pellet exits, the vibration is there, but you can’t see it because it’s been integrated out. The graphs in my article were direct measurements of velocities, and showed all vibration, but had I measured accelerations and integrated the data, the vibrations would be greatly diminished, if they showed at all.

We might know more about hold sensitivity next year. Nomads are hosting the inaugural UKAHFT 2019 Recoil HFT Championship on 26^th May, and there will be plenty of rifles with short strokes, light pistons, reduced diameter cylinders and the like. I just need to convince the owners to let me test their rifles…

[TonyL]

X= along
Y = up and down
Z = side to side

See the "Y" muzzle flip in the last graph...

Gotcha.