Hi All I have a very early FX Crown (in the first 500 made) It has the 8mm reg piston - I only mention that to date it.
Now I have been out of shooting it for a while and it used to be an good gun and Shot JSB King Heavy MKII’s best at about 800fps and 120bar reg, this was how it came from the factory with a 600mm barrel.
I wanted to experiment with slugs. I watched all the usual Youtube suspects re tuning and got to work practicing on pellets first. In the end I got to about 155 bar reg pressure and had effectively maxed out the HST, on the MAX setting. it was shooting the MKII’s at about 930 fps but it sounded terrible, it wasn’t consistent, or accurate with the extra distance I could now achieve and I realised somewhere down the road I’d turned into a blind alley and this was just not right…
So Ive left the HST on almost Max when it was on MAX on the dial. I then reduced the Reg pressure to 100 bar, to start again. I had a tin of the lighter JSB Kings and started using them to experiment with. With my reg at 100 bar Im getting about 910-920fps with the HST at the “MIN” setting on the wheel.
Now here is what I really cant get my head around, and is making me question what I think I know…
When I keep the reg the same and increase the HST the FPS falls, and it does so linearly in line with the increase in HST so at the “MAX” position on the wheel I get 720ish FPS. Also the sound of the gun changes and becomes quieter and more “dull” less of a pop or crack and more of a hollow “thud”. what is more this is very consistent, if I turn the HST back down I get 920, back up I get 720. its not just all over the place
I thought that HST would increase FPS if every thing remains the same, or at very least it would not increase FPS, but to significantly reduce the FPS??? this makes no sense and I cant fathom how the mechanics of this would play out. I get that increased reg Pressure provides more resistance to HST so you get a shorter open duration on the valve and results in a decrease in FPS, but Im not touching the reg…so what gives
Can someone help me understand why this is? I thought I understood this, well until today!
Regards
SOTL
Now I have been out of shooting it for a while and it used to be an good gun and Shot JSB King Heavy MKII’s best at about 800fps and 120bar reg, this was how it came from the factory with a 600mm barrel.
I wanted to experiment with slugs. I watched all the usual Youtube suspects re tuning and got to work practicing on pellets first. In the end I got to about 155 bar reg pressure and had effectively maxed out the HST, on the MAX setting. it was shooting the MKII’s at about 930 fps but it sounded terrible, it wasn’t consistent, or accurate with the extra distance I could now achieve and I realised somewhere down the road I’d turned into a blind alley and this was just not right…
So Ive left the HST on almost Max when it was on MAX on the dial. I then reduced the Reg pressure to 100 bar, to start again. I had a tin of the lighter JSB Kings and started using them to experiment with. With my reg at 100 bar Im getting about 910-920fps with the HST at the “MIN” setting on the wheel.
Now here is what I really cant get my head around, and is making me question what I think I know…
When I keep the reg the same and increase the HST the FPS falls, and it does so linearly in line with the increase in HST so at the “MAX” position on the wheel I get 720ish FPS. Also the sound of the gun changes and becomes quieter and more “dull” less of a pop or crack and more of a hollow “thud”. what is more this is very consistent, if I turn the HST back down I get 920, back up I get 720. its not just all over the place
I thought that HST would increase FPS if every thing remains the same, or at very least it would not increase FPS, but to significantly reduce the FPS??? this makes no sense and I cant fathom how the mechanics of this would play out. I get that increased reg Pressure provides more resistance to HST so you get a shorter open duration on the valve and results in a decrease in FPS, but Im not touching the reg…so what gives
Can someone help me understand why this is? I thought I understood this, well until today!
Regards
SOTL