Canadian Airgun Forum

Does the piston seal make contact with the end of the compression tube during normal operation or is that considered pistom slam? Or is the piston/seal supposed to fall just short of the end of tube due to air resistance

IMO, of course the piston head will touch the tube eventually as there's nothing in between the end of the tube and the piston except the main seal.

And what help to preventing the piston slams on the end of the tube is just the compressed air...

So you can figure out how to make them touch each other gently then...

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~Plinkers~
FX-M3-22 Compact#PP700-Carbine#Diana48-177#XS28M-25@26fpe#HW45 Beast#AW-Custom Z-Killer DE
~Competitors~
FWB300SU#Tau-7#IZH-46M#FWB-65#CP88-C
~Target~
HW 30s/35e/97k/40+Extender/P3+Scope/70#CZ200s Laminated@10fpe#AA ProSport-177@12fpe

The piston is supposed to slow down on the cushion of air as it compresses it. When the piston is too light or the pellet is too heavy, the piston can bounce off the cushion. It causes bad accuracy, poor velocity, and it's hard on the spring. Extra light pellets can cause the piston to slam into the end of the compression tube since there isnt enough inertial mass to allow the cushion of air to build. That's why the high velocity ultra light pellets are hard on your gun. To clarify, I'm talking about high velocity springers.
Tuners strive to get piston weight, pellet weight, and velocity in the right mix so accuracy is good, recoil and hold sensitivity is minimal, and spring life is long.
Hope this helps.

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Theory is when you know how something works, but it doesn't.
Practice is when something works, but you don't know why.
In my shop, Theory and Practice are combined!
Nothing works and I don't know why.

Two lathes and too many projects

Good info guys.
Is there any simple way for an inexperienced tuner to know if they are getting bounce on slam?
I would guess that these would be pretty subtle.
Thanks
Rob27

Piston bounce IS more subtle but once you get used to your gun and you load it with a TOO heavy pellet...it will sound and feel like a thump inside the gun ..hard to explain but definitely noticeable....Piston slam is easy to detect and not subtle...its a "clank" sound you won't want to hear twice from your gun

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The cave you fear to enter....holds the treasure you seek

Let's consider a high velocity .177 and assume about 920 fps with 7.9gr pellets as it comes out of the box. If you shoot pellets that weigh less than 7 gr, you're going to get some piston slam. The lighter the pellet, the more piston slam will occur. On the other end of the spectrum, a too heavy pellet will result in a significant loss of velocity (more than you would expect with a heavier pellet). There are YouTube videos that show the pellet exiting the barrel, followed a few milliseconds later by a puff of air as the spring forces the piston back to the end of the compression tube, expelling the air that was left after the piston bounced. I'm guessing that about 15 grains is the break point for heavy pellets in a springer. Someone with more experience than I have could chime in here and tell us if 15gr sounds right.
On another note, gas rams (nitro piston, etc) do not seem to be unduly stressed shooting heavy pellets. Light pellets don't seem to hurt gas rams either, but the piston seal is going to get beat up shooting ultra light pellets.
Most of my high velocity springers are detuned slightly to find the "sweet spot". Only two of them shoot well at a full velocity tune.

Edit: I don't shoot ultra light pellets in my high velocity springers.

_________________
Theory is when you know how something works, but it doesn't.
Practice is when something works, but you don't know why.
In my shop, Theory and Practice are combined!
Nothing works and I don't know why.

Two lathes and too many projects

Ricksplace - are you referring to a 15gr. pellet in .177 cal. as being max?
Most pellets in .22 cal. are over that weight.

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Best Wishes
Daryl