How can a 'bad' piston seal effect accuracy?

[UlteriorModem]

I was wondering how a bad piston seal or breech seal could affect accuracy?

I get it if the FPS are all over the place, but what if the fps are pretty consistant? As in the defect is defective the same each time?

How could some loss in efficiency and or pressure effect the actual accuracy?

[Novagun]

I suppose if the loss of power with deficient seals is exactly the same each time you shoot then accuracy should be the same. I have experienced no loss of accuracy with a broken spring. Maybe better because of the lesser recoil.  However with  deficient seals you get reduced muzzle velocity. That reduction will reduce the spin rate of the pellet and that could affect accuracy. The overwhelming factor though is that damaged seals produce inconsistency
You also get near enough to the same recoil with reduced power so there must be some correlation between power and recoil that makes magnum guns harder to shoot.

[mobilehomer]

Also with a bad seal, the piston slams forward a little harder. Maybe not enough to feel, but the pellet feels it.

[Roadworthy]

You didn't define bad in what way.  If the seal has a nick or a tear it will allow some air to escape while compressing the rest of the air to drive the pellet.  As the compression tube and seal heat from use the same amount of air may not be bypassed each shot.  Depending on the flaw the leak may even seal itself at times.  The result will be inconsistent vertical stringing.  Go buy a new seal.

[UlteriorModem]

I was speaking in general really.

But here is a seal that came out of my Titan

20190430_203839 by Tom Whit, on Flickr

20190430_203845 by Tom Whit, on Flickr

20190430_203850 by Tom Whit, on Flickr

[Mark 611]

yep that's need a new 1!!

[nced]

I was wondering how a bad piston seal or breech seal could affect accuracy?

I get it if the FPS are all over the place, but what if the fps are pretty consistant? As in the defect is defective the same each time?

How could some loss in efficiency and or pressure effect the actual accuracy?

Picture worth a thousand words?...........

Personally, I've never noticed much degrade in accuracy when factory piston seals erode (burnt through is another issue), however I did notice a change in trajectory and a few shots over the chrony showed that the pellet velocity was indeed "lower than usual". I personally believe that this issue is a result of erosion at the transfer port reducing the "swept volume" on the compressed air just before the pellet "pops the leade". LOL.......ONE of the reasons I like my home rolled aluminum oring sealed piston caps is because the face of the seal won't erode and the actual seal (an oring) is shielded from the hot high velocity air at the transfer port.........

[Mossonarock]

nced, That is a right smart piston cap.

I've heard of but have never seen nor do I know of any guns by name that have a metal piston ring for a seal much like the piston rings in a car engine.
With those, there is no plastic or rubber at all. I'd like to learn more about such air rifles. Like I said, I don't even know what models of airguns have those. Are any even currently being manufactured?

[Airnut]

yep that's need a new 1!!

Agree it’s trashed!
What bothers me is a lot of the damage looks like you had some trash in the cylinder?
What does the cylinder wall look like? If it’s scored up a new seal may just be a bandaid.

[nced]

nced, That is a right smart piston cap.

I've heard of but have never seen nor do I know of any guns by name that have a metal piston ring for a seal much like the piston rings in a car engine.
With those, there is no plastic or rubber at all. I'd like to learn more about such air rifles. Like I said, I don't even know what models of airguns have those. Are any even currently being manufactured?

My actual seal is a military spec Viton oring, however the FWB300 match rifle does have a metal piston seal like an automotive piston..........


LOL.....the receiver of my HW95 and Beeman R9 aren't nearly precise enough for a metal piston seal and even when I'm oring sealing a HW95 I need to hone the receiver ID to be suitable for my 020 size rubber orings.........

[UlteriorModem]

yep that's need a new 1!!

Agree it’s trashed!
What bothers me is a lot of the damage looks like you had some trash in the cylinder?
What does the cylinder wall look like? If it’s scored up a new seal may just be a bandaid.

I thought so too, so I inspected the chamber carefully and it was quite clean, just to be sure I cleaned it 'again' with some brake cleaner before lube and re-assembly. The only scoring is where the metal body of the piston was contacting the chamber walls.