I just purchased a Nikon Monarch 4-16x42 with BDC for my .243 WSSM. I was reading the direction and am a little confused about how this scope functions. Basically, do the zoom power effect the BDC. For instance, if I find that the 3rd circle is my 400 yard hold point and I use 16 power to sight in. Do I always have to shot 400 yards with it on 16 power. If I turn the scope back to 10 or 12 will can I still use the same hold point for 400 yards?

Should say it in the owners manual. Most of those type scopes have to be set to max power for it to work like advertised.

One more thing to add is the fact that unless the scope was designed for that caliber of rifle, it's accuracy will be affected - by it's adjustments.

From what I remember, most rifle scopes of that design - unless supplied with different adjustment knobs = are really designed for a 30/06 type of rifles ballistic's.

If you have a rifle that has less bullet drop, you really cannot go by what the manufacturer claims for adjustment by range.

What you will find out is that if you want to know where it is going to hit, you are going to have to spend time at the range and shoot it until you can develope a score card that will give you an estimate of how much to adjust it to get it to hit where you want it to.

Basically the same thing that snipers and the military does with their scopes.

Typically, holdover or range finding scopes with reticles in the 2nd image plane need to be used on the highest magnification setting. Even utilizing manufacturers' data, you still need to shoot / test with your equipment.

The power of the optics has nothing to do with with the line of sight, You just have a largerobjectivepicture .

As for the circles they are only an approximate zeroand will vary with each caliber , bullet weight or gun you put the scope on . Just need to do a bit of shooting as Bugs said . Luck

I have a leupold B&C and a swarovski TDS......the swarovski crosshairs work at any magnifcation, the leupold only work at max magnification, which is fine because those additional crosshairs are at 300,400,500yds....and really at that range.....I'll be at max magnifcation, though it is ncie that the swarovski works at any mag.....though at 2 or 3power those crosshairs are tiny.

Also the leupold has 2 settings to work with differen calibers, so kinda like at full mag for a certain category and at like just undre full mag another category.

The scope/booklet should explain it quite well, but im assuming the BDC reticle probably only works at full magnification? though if for a muzzleloader with max range of 250yds im not sure.....how that would work.....

Most calibers will work....you just have to find the right bullet setup.....so sometimes you end up wanting a bullet with more drop.....vs.... a flatter shooting one, if it matchest your mult crosshairs better.

My swaro TDS kinda requires me to shoot 225gr vs. 250gr, though 250 will work wll, the 225 are dead on the money!

I'm quite sure you can find a load to work with the scope and the .243wssm

BDC's are garbage just a salesmans feature to sell scopes to those guys that know they can't shoot. They tell ya zero it at 100 at buy a range finder and you will beable to shoot like carlos hathcock. Bull Puckey.... No easy way around learning how to judge range and shoot accurately unless you simply practice.