With a non-regulated PCP rifle, there will usually be a few slower shots after a complete fill, then the velocity will climb and move in an arc upwards, then down as the pressure in the tank depletes. Adjusting the fill pressure to the start of this velocity arc & recording at what pressure the velocity again crosses the starting speed, (within 5 or 10%) will give you the range of pressure your rifle works best at. For example, Gord fills his non-regulated Air Force Talons to only 2,600psi and re-fills them to the level once reaching 1,500psi or between 1,500psi and 2,000psi to stay in the "sweet spot" for accuracy. The hammer spring tension on these rifles is adjustable. The 'range' from bottom to top is about 150fps actual speed. Somewhere in there, will be the best setting and this can only be learned by shooting - a lot.
With a regulated rifle, the pressure on the valve is constant, but if the hammer spring is too hard/stiff. air will be wasted - there must be a balance between regulator pressure and hammer spring tension, so as to not waste air. There is also a balance between those two, and the transfer port size, which restricts the final amount of air to propel the pellet. If that hole is too small for the amount of air expended from the regulator, air is being wasted, flowing out the muzzle AFTER the pellet has been discharge.
That is as I understand this phenomenon of PCP air rifles.
Some guns, like the FX say not to shoot the rifle below the regulator setting. At roughly full power, my Dreamline 'gets' about 44 shots, if I remember correctly. At low power, with the regulator turned down to 100 bar from 135 bar, along with the transfer port turned to it's "low" setting (it has low, med and high),yet leaving the hammer spring almost at max, I get 151 shots, from full down to 100bar. I am still likely wasting air due to the high hammer spring setting, but you cannot argue with the shot count. In .25, these should be running between 500fps and 600fps judging from videos on the net.
_________________ Best Wishes Daryl
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