Ballistics/Scope Question

[Rem 700]

I was wondering if anybody could solve this debate for me (between my friend and me). I bought a Ballistic Compensation Scope that has one hash mark above the crosshairs and two hash marks below the crosshairs. I zeroed in the crosshairs at 150 yards and with 9x my hashmark above the crosshairs is on at 100 yards. My question is about changing the adjustable power setting on the scope. Will changing the power (like to 3x) still allow me to use the top hashmark at 100 yards? On 9x at 100 yards my top hashmark is 2.5in above the crosshairs on the target. However, if I drop my power to 3 at 100 yards my top hashmark is more like 6-7in above the crosshairs on the target.
So is this just in my mind, or do I need to keep the scope set on the power that I sighted in all my ballistic range marks with?
Thanks.

 

[Antelope_Sniper]

Rem, with most scopes the answer is no. Normally the crosshairs are a fixed size in the reticle regardless of the magnification. As you decrease the magnification the distance between the hashmarks at a given range increases. As an example if the distance between the marks is 3" at 100 yards on 9x, they would be 9" apart on 3x. This would lead to significant different points of impact when using the hashmarks.

There is a way to test this. Put a gradiated target out at 100 yards, such as the Redfield sight-in targets. Measure the distance between hash marks on 9x. Decrease the magnification to 4.5x The distance will between marks will probably be twice what it was before.

If on the other hand the size of the crosshairs changes, and the measurement stays the same, then you have a "first plain" reticle, and the hashmarks can be used the same at any magnification. The easier way is probably to just look on the box. If it doesn't say "first plain reticle" chances are it doesn't have one. If it did have one, the guys in Marketing would want to make sure you were aware of it.

 

[JD338]

Antelope_Sniper is spot on. Depends on the make of the scope and if it is a First plane or Second Plane reticle.
What make and model scope are you referring to?

JD338

 

[Rem 700]

My scope is just the basic Traditions Ballistics Scope that comes with the Pursuit XLT muzzleloader...it is only a $50 scope...so I would guess it is not a First Plain...
Thanks for the info...
Just got back from an elk hunt in Colorado. Killed a cow. I'll post the pics once I get them downloaded...