Sheridan "tuning".

[Jordan]

My sheridan pistols barely will pierce a 12 gram. Like just a little pinhole in the 12gram face is what I'll see. Normally takes 2-3 strikes to pierce. 25 shots per 12gram that way.

Took two shots to pierce with the current spring setup. How many usable shots out of that 25, ie: 260fps?

[Jordan]

A barely visible hole is still functional. That's when the piercing is iffy, so it's usually a little larger. It should be the point through the seal. Does the valve body have a cone on it that the pin travels through? That's a big dish around the hole.

Cone? Not sure what you mean.

[Spider!]

I'm just confused by the pic of your 12g.

I'm expecting the seal to be flat with a hole in it. The cavity around the pin hole is odd to me.

[Jordan]

I'm just confused by the pic of your 12g.

I'm expecting the seal to be flat with a hole in it. The cavity around the pin hole is odd to me.

Could it be the brand (Crosman)? No idea, to be honest, it's a stock Sheridan setup with a PPS seal kit, including face seal.

If I throw a spent 12gram back and pump/shoot a few times that cavity (and hole size) get larger... I just cycled a new 12ie through and the pin hole is, well, a pin hole, if I pull the 12ie out after 25 or so shots, still with plenty of liquid spewing for a second or so.

I'll chase it next year, once the weather warms up... we're in the single digits here now (Celsius, mind you, not Freedom Units) so not much point doing much more.

I've got a few things to consider, at least.

[Falcon16]

shoot me a call later on Jordan, I can give you a hand, I'm off work at 9:30

[Jordan]

Appreciate it, but I'll likely be turning in for the night around then.

[Falcon16]

Ah ok no worries, I'm off tonight at 6:30

[Spider!]

Could it be the brand (Crosman)? No idea, to be honest, it's a stock Sheridan setup with a PPS seal kit, including face seal.

If I throw a spent 12gram back and pump/shoot a few times that cavity (and hole size) get larger... I just cycled a new 12ie through and the pin hole is, well, a pin hole, if I pull the 12ie out after 25 or so shots, still with plenty of liquid spewing for a second or so.

I'll chase it next year, once the weather warms up... we're in the single digits here now (Celsius, mind you, not Freedom Units) so not much point doing much more.

I've got a few things to consider, at least.

Ah, ok. I kind of thought the face seal would stop that. I'm thinking a shorter but stiffer spring behind the valve. The valve travel is long,

Make sure your bolt passage matches up with the body. You have lots of valve travel, so I'm wondering why the gas isn't getting to the ball

[Jordan]

Ah, ok. I kind of thought the face seal would stop that. I'm thinking a shorter but stiffer spring behind the valve. The valve travel is long,

Make sure your bolt passage matches up with the body. You have lots of valve travel, so I'm wondering why the gas isn't getting to the ball

With the valve out and bolt in, I can look through the bottom retention hole I drilled and see the bolt passage... as far as I can tell, everything lines up.

[gabe]

Valve travel is definitely on the long side. With Crosman 12grams there's no "cone" indentation around the pierce hole, just a hole. The cone makes me think the valve is being opened too far and the pierce pin is going too deep causing that conical indentation. The excess dwell certainly would explain your gas usage. Normally you can tell excess dwell by how much gas vapor is vented out of the barrel. With perfect tuning the gas has pretty much expanded by the time the ball clears the barrel and there is very little gas vapor that gets expelled. Too much dwell and you start to see a very clear cloud of gas. CO2 of course always makes a decent sized cloud so that makes it harder to judge than HPA.

My PMI-1 at 260 gets 25 full power shots and then up to another 15 increasingly weaker shots. Stock everything, no rva, no widgets, bone stock. My Palmerized P68sc gets 20 full power shots at 280 then it falls off more rapidly and gets maybe another 10 shots that are marginally usable.

[Jordan]

Valve travel is definitely on the long side. With Crosman 12grams there's no "cone" indentation around the pierce hole, just a hole. The cone makes me think the valve is being opened too far and the pierce pin is going too deep causing that conical indentation. The excess dwell certainly would explain your gas usage. Normally you can tell excess dwell by how much gas vapor is vented out of the barrel. With perfect tuning the gas has pretty much expanded by the time the ball clears the barrel and there is very little gas vapor that gets expelled. Too much dwell and you start to see a very clear cloud of gas. CO2 of course always makes a decent sized cloud so that makes it harder to judge than HPA.

My PMI-1 at 260 gets 25 full power shots and then up to another 15 increasingly weaker shots. Stock everything, no rva, no widgets, bone stock. My Palmerized P68sc gets 20 full power shots at 280 then it falls off more rapidly and gets maybe another 10 shots that are marginally usable.

How do I limit travel? Stiffer valve spring? Weaker main?

[gabe]

What kind of velocity are you getting? A lighter hammer would be the best way to limit dwell. A stiffer valve spring would work too but you may have to go up on the hammer spring as well to keep the velocity. So it has stock springs? I've heard PPS main springs can be overly long and need to be trimmed.

[Jordan]

What kind of velocity are you getting? A lighter hammer would be the best way to limit dwell. A stiffer valve spring would work too but you may have to go up on the hammer spring as well to keep the velocity. So it has stock springs? I've heard PPS main springs can be overly long and need to be trimmed.

Stock mainspring that I've trimmed down, and stock PPS valve spring.

I did swap in a trimmed down red Nelson valve spring which seems to have made a bit of a difference, but I'll double check velocity later.

[Jordan]

As an update:

I added a RVA to the trigger group and swapped in a Bluestreak single lobe trigger with a spare PPS Typhoon hammer I've had for years, in hopes that it was somewhat lighter than a stock KP hammer.

I seem to be the right path - I seem to have a consistent number of "good" shots but still want to at least shoot a whole sidetube off over 260fps, if possible.

How do I limit travel? Try a harder valve spring or physically limit the cupseal from traveling via shims? I'm just trying to wrap my head around some of the suggestions and observations made in this thread and make sure I'm understanding everything being said.

I'm sure I'm currently handicapped by the weather - it's not quite at the freezing mark, but I think I'll see better results when I'm in the double digits (Celsius, mind you). 🙂