USFT Fill Question

C

cris

Guest
I fill my USFT to 1500 - 1600psi. The first few shots are very low after the fill, maybe 2 pellets low, until I get to 1200 - 1300psi. As I understand it, this might be normal but is there a solution other than re-zeroing the scope? Thanks.
 
As a follow up, the groups are small and round if I use the same POA, the group is just low. Takes approximately 12-15 shots to get back into the groove. Thanks.
 
on my Walther after changing the cylinder, it takes 2 or 3 shots to get the regulator back up to snuff. Logun exhibits something similar after recharge. Have not noticed it on ANZ 2002CA.
 
Try a starting fill of 1300 to 1400 and see if your POI stays the same. If it does use that as your starting fill pressure and count the number of shots you can get before your POI starts to drop and make a note of your ending pressure. Your sweet spot or heart of the fill is probably lower than the suggested starting fill which is normal in some cases. My USFT / Hunter is no where near the recommended starting fill it just depends on what the gun wants.
Doug
 
Doug,

Thanks. My Hunter goes down to under 1000psi before I see any change. Seems counterintuitive that a fresh fill would cause shots to go low. Definitely a sweet spot for the fill numbers.
 
Seems counter-intuitive?

Most un-regulated guns, exhibit this trait. Its because the firing valve opens with greater difficulty against higher pressure, and so opening is shallower and it is closed more quickly as well, thus giving less time for the air to flow. As reservoir charge pressure is lowered, the valve can open more easily, and thus a bit farther, and to aid this, the valve stays open a bit longer, due to the deeper opening and less forceful closing.

I designed the USFT valve to operate pretty well over a relatively narrow range of around 350psi or a bit less, and, to a degree, the midpoint of this range varies between 1100psi and 1300psi based on several factors, but the end result is about the same for a standard sized gun .... around 45-60 good shots in the 18-25fpe level (depending on caliber). A well set up one will deliver shots with the same sort of consistency as about any other airgun I've tested at similar velocity and shot count per charge, and do it with amazing reliability.
 
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