Can't help with the B&C reticle, haven't used it. Their website has more info I think. All I'm saying is hold on to that woman. Didn't just buy you a rifle, bought you a great rifle!!!!
I've had one for a few years and it works although at times I find it somewhat aggravating.
Basically you zero the rifle at 200yds and shoot as normal to that distance. For a longer range shot, you determine which "delta" your round falls into per their guide (not sure what a .338 is but I'm guessing "big delta" based on typical MV- some cartridges have multiple bullet weights that change which one you use). Their guide has a pretty good list and you can match trajectories to something similar if your exact combo isn't listed.
For a long shot using the reticle you set the power ring to the correct "delta" and you're set for the reticle from 200 to 500 yds on the hash marks. For example my .308 with 180s is a "big delta" round and I set it on the large triangle at 8x. The .308 165gr LM rounds are "small delta" and I set it at 10x.
You have to have a reasonable range to your target for it to work right. I dislike the internal rangefinder using the power ring and duplex to estimate yardage. I've used it on the range and it works better than kentucky windage or guessing but its not perfect IMHO.
The whole thing is not terribly complicated but its a lot to keep up with in the field and I blew an opportunity 2 years ago by fiddling with the thing when I should have been shooting. I've since went to a fixed 4x on a .300 WSM- plan to get within 300yds and just shoot it.
If you want me to talk it through on the phone with you send me a PM with contact info. The whole bit is not very intuitive in my opinion but it does work.
Does said wife have a good looking available sister? Seriously though what a nice gift!!!! There should be instructions that came with the scope. I would also imagine leupold would have plenty of info on their website.
In a nutshell...your 300, 400, 450, and 500 marks will be calibrated for your ctg. on the high end triangle...10X
Here's an example:
My 7MM-08 is a low velocity ctg. My 4.5X14 B&C has calibration triangles on 11X and 14X. I have to use 11 or 12 power for the calibration to work.(and it does)
If I use 14X, my shots hit 12" low at 450 yards. The higher power calibration is for the higher power calibers(muzzle velocity), and thus, the bullets would be hitting higher.
Your owners manual will tell you which setting to use for your class of ctg.(.338WM.) I would think it's 10X. This would apply to all shots longer than 200 yards.