Originally Posted by
HollowPoint
I've wondered about some of the fps numbers posted around the internet; even on the "Tuned" Big Bores.
I realize that we're talking about an air reservoir that reduces in psi after every shot so, it stands to reason that the fps numbers would go down in more of a linear way. What I mean is; as an example; each shot dumps 200 psi. So, this would mean that your shots would slow down incrementally because there is less air in the reservoir to draw from.
Some of the numbers I've seen will start at a certain level, (generally the highest fps in the shot string) then the next shot may be a little higher than the first, then back down, then a couple shots higher still. It's rather erratic to say the least.
I can see why this might happen with traditional firearms where there are many components such as brass, powder, primers, seating depth, runout, reloading inconsistencies etc.. In an airgun, where an air valve should open up to or near the same amount each time the trigger is pulled, such a fluctuation in fps just doesn't add up.
I'm starting to come to the conclusion that it has to do not with the function of the valve, trigger, hammer or spring but, it's the position of the projectile in the chamber at each shot.
When we load a bullet into the chamber, is it pushed all the way in to the same spot in the chamber each time? With round ball especially; it can be a good fit in the bore but, while in the chamber -which is generally a looser fit- if it moves even a little bit it's bound to effect the fps as well as accuracy.
Now, I know that there are some that will argue that they've been getting fairly good consistency and accuracy from their air guns by just loading a bullet in the chamber without fiddling with the exact position of their projectile in the chamber but, that's not the point I'm trying to make.
If they're getting good accuracy that way; good. That's better than good but, I'm talking about the up and down variance of the fps numbers. Up where you wouldn't expect them to be and down where you'd expect slightly higher numbers.
I admit there are alot of variables that I'm not taking into consideration with these observations about fps but, what do you guys think?
HollowPoint