'How" would one use a gun on different power settings?

I am new to PCP air rifles, and from my understanding, here is how it works (simplified):

You get a gun, you get a scope, you Zero the scope at a desired distance, you pick a bunch of different pellets and you start shooting. What ever pellet "works" the best, you stick with that. If you shoot further than you zeroed your gun at, you aim higher. If you shoot closer to your "zero", you aim lower (I guess???). Anyhow, that should be it. Right? (And if it is not, don't worry about it, I am going somewhere else with this).

Now, what happens if you have you gun dialed in to a certain distance and pellet, and you lower the power!? How would I "know" where the pellet will go? I mean, you can try it and make notes, but is that the way to do it? Sounds like a pain considering that some guns have 6 different power settings...

Thanks,

Kmd

EDIT: How to you compensate for a now different bullet drop when lowering the power? (I know, I could have just said that, ha ha).
 
Honestly, the only way to know where the pellet will hit if you adjust the power on the gun is to shoot targets at the same distance you zero'ed the rifle at and make notes. For example, I shoot PCP's with variable power including Air Arms and Brocock. If I adjust the power level, I need to shoot the gun and determine where the pellet will hit. Ideally, if the power is the only thing adjusted, the pellet should either track up or down on the vertical plane of the scope crosshairs. However, I've had instances where some pellets will perform better at certain velocities. For example, shooting a 10.6 grain 0.177 pellet out of my Air Arms S500 at medium power produced 1/2" groups at 30 yards. I cranked up the power to max and my groups tightened up and my shots landed higher on the vertical plane of the scope crosshairs. 

Bottom line: Go shoot your gun with the same pellet at various power settings and make note of where they land on the target - only way to know what to expect of your gun when you do this in the field. 
 
Hey Doc,

Thanks for the input. What you are saying makes totally sense, and I figured it would something "simple" as that... But I had to ask.

I had my eye on the new MTC Viper Pro ever since it was announced, and I am wondering, if it makes even more sense now to get one!? Being able to print your custom tape for the top turret looks liked it would really help. No need for notes, you just print a custom tape with the correct markings on. I guess. : )

Thanks,

Kmd
 
Dr Beretta is spot on, you have to do the range testing and make a card for different settings and pellets. Another option would be to start at the optimum power level for a particular pellet, shoot a magazine, crank the power up a notch, and repeat till you're low on air. A lot of folks do this with the very powerful guns like the Sumatra. If you want to get precise with your fill pressure and shot count you pretty much need a chronograph. I've avoided owning one so far, but borrowing one isn't working for me any more....
 
If you're interested in getting a scope, I'd suggest you get one with mil-dots (lots of options out there) and download the free Hawke ChairGun Pro computer or phone app which will allow you to enter in your scope/gun specs, pellet type and weight, etc, and then you print out scope caps with the yardage markers next to the mil-dots so you can quickly reference your aim point based on yardage. It will require you to know your pellet velocities, so a chronograph will be in your future or you can get by with a phone app that uses sound to determine velocity (less accurate). Also, a rangefinder may be helpful down the road to get precise distances to your targets. 

The poor-man's way of doing this would be to skip the software, skip the chrony, and just go out and mark out precise distances to various targets, shoot the gun at those distances, and make note of the drop of the pellet at various distances as they relate to your mil-dots as you look through the scope.

Regardless, be aware that changing the zoom on most scopes will also change the mil-dot corresponding yardage markers. For example, what may appear to be a two mil-dot holdover at 9x on the scope for X-yardage, may be a one mil-dot holdover at 4x for the same X-yardage. Hope this helps. 

http://www.hawkeoptics.com/chairgun.html

 
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Thanks everyone for the input and the tips!

I guess I am going to just start small, get a better scope and go from there. Without any other "gadgets" as of right now, I am going to be forced to test at different ranges, and make notes. Since I am only shooting in the backyard for now, I am not worried about having to test 1000 different distances. So that's not too bad. I guess after that I will be looking at getting a laser range finder and the app for my phone. 

Having said that, I wonder if one could use a Scope with build in Laser Range Finder and Bullet Drop Compensation, such as the Bushnell or Burris one?

Thanks,

Kmd
 
I have an FX Royale with the 3 setting power wheel. What I do is zero it at my desired yardage on high power then zero my scope elevation knob there. Then I'll do the same on medium power but I don't re-zero the elevation knob, just record how many clicks to get to my medium zero. Same for low power. Then I use Chairgun or range cards to figure out my hold over/under for a particular power and yardage combination. I could also adjust the elevation and not have to hold over/under, but I find it easier not to adjust the scope for each shot. My scope is FFP, but the same works for a non-FFP scope. For me FFP just makes the hold over/under easier since it's the same for any magnification.