Regulated S400 - odd POI results for 25m benchrest

[Blackbaronfish]

When the hammer strikes it comes against the force of the air in the cylinder and lets out a slug of air. As the cylinder pressure reduces the hammer will let a bigger slug of air through.This results in a higher point of impact. This change shouldn't happen in a regulated rifle as the regulator should keep the pressure even!.
What regulator pressure is your gauge showing?
The way forward is to do a full chrono string with weighed pellets. Fill to 210 bar and record the shots.


BBF

[mrgeoff]

Took the barrel band off, sprayed 5 pellets across the target. I did wonder if this was good advice, with the long and seemingly very twangy barrel.

Put the barrel band back on.

When I last tested, I went from approx 160bar down. Today I went from approx 200.

After about 10 shots go get zero again, I started a BR card spot on zero, then the POI dropped gradually over the first 25 pellets, and then after another 15, the POI came back up to zero....
Next was 35 pellets POI on zero, then they started to drop again and 10 pellets later it was off the reg and dropping 2 inches on the last pellet.

So from a full fill, maybe 90 shots which isnt bad, but a very unusual the POI dropped then came back up! If it was non-regulated, it would be the other way round!

Everyone tells me to drop the regulator pressure down from the 125bar that Altaros recommend? Why do Altaros reccomend, and set the reg pressure at 125bar, if its not right?

I guess I have to try it anyway, no one will let me sleep unless I do.

[Knockedover]

Out of curiosity is the cylinder floated in the stock? I've played with several 400s over the years and a slight movement has often been cured by making sure of good clearance around the cylinder.

[mrgeoff]

There is some foam tape between the cylinder and stock.
Will remove this.

[RobF]

Took the barrel band off, sprayed 5 pellets across the target. I did wonder if this was good advice, with the long and seemingly very twangy barrel.

Put the barrel band back on.

When I last tested, I went from approx 160bar down. Today I went from approx 200.

After about 10 shots go get zero again, I started a BR card spot on zero, then the POI dropped gradually over the first 25 pellets, and then after another 15, the POI came back up to zero....
Next was 35 pellets POI on zero, then they started to drop again and 10 pellets later it was off the reg and dropping 2 inches on the last pellet.

So from a full fill, maybe 90 shots which isnt bad, but a very unusual the POI dropped then came back up! If it was non-regulated, it would be the other way round!

Everyone tells me to drop the regulator pressure down from the 125bar that Altaros recommend? Why do Altaros reccomend, and set the reg pressure at 125bar, if its not right?

I guess I have to try it anyway, no one will let me sleep unless I do.

Floating the barrel shouldn't cause scatter unless it's loose or something on it is loose. Try sticking some weight on the end.

What pressure is it dropping off the reg? If it's well before it could be the reg pressure is contributing to the valve closing. Although regs supply the same amount of pressure, as their input pressure changes their response speed can change leading to different behaviour over the charge. Some valves will self regulate the speed but either the gun's recoil or the pellet in the breech is affected in a different way causing a poi change. Without changing the reg it's possible to change this but not sure of how this setup is setup.

Walthers show a drop in poi before the reg pressure is reached, you can't see it on the chrono though. It's possible and quite easy to tune that out.

[RobF]

Putting the reg on a tester would show you if it's ok. You can look for creep and stability over a charge with a decent gauge.