Fill pressure on an unregulated gun is a function of the tune. With the stock tune I filled my Prod to 2500 because that was only slightly higher than were it got peak velocity. You could just fill to the peak but the shot string would be shorter than filling slightly higher if you measure your shot string as the number of shots at a given velocity variation. I increased my transfer port size and found I could utilize the full 3,000 pressure but only with 7 turns in on the hammer spring. That got me nearly 20 ft lbs but also only about 10 shots. So I currently shoot it at 700 to 750 fps with 14.3 or 14.66 grain pellets for 17-18 ft lbs. I get about 20 shots at pretty stable velocity. My fill pressure is 2700.
My process to decide fill pressure is to shoot a shot string while measuring the velocity (I use a cheap chinese chronograph after shooting my old chronograph, about $35 off Amazon) and then look at what will give you a nice shot curve for what you want to do. Once you have the data it doesn't take long to analyze. I look for a maximum spread of around 40 fps - 20 up and down from the average. Some guns may do better than this for a nice long shot string.
With the Avenger I shoot targets as I measure the velocity (the Prod doesn't like this, the Avenger doesn't care much - the chinese chrono clamps to the shroud). I am looking at the velocity at the regulator setting and then increasing hammer spring tension to see what happens to both velocity and accuracy. It is also possible to vary transfer port size and barrel port size on some guns. Increasing the port diameter increases velocity.
My process to decide fill pressure is to shoot a shot string while measuring the velocity (I use a cheap chinese chronograph after shooting my old chronograph, about $35 off Amazon) and then look at what will give you a nice shot curve for what you want to do. Once you have the data it doesn't take long to analyze. I look for a maximum spread of around 40 fps - 20 up and down from the average. Some guns may do better than this for a nice long shot string.
With the Avenger I shoot targets as I measure the velocity (the Prod doesn't like this, the Avenger doesn't care much - the chinese chrono clamps to the shroud). I am looking at the velocity at the regulator setting and then increasing hammer spring tension to see what happens to both velocity and accuracy. It is also possible to vary transfer port size and barrel port size on some guns. Increasing the port diameter increases velocity.
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