Help with focal planes [Archive] - Glock Talk


View Full Version : Help with focal planes

03-26-2010, 11:39

I would like to put together a .308 bolt action for distances up to 1000 yards. I'm a little unsure of what kind of scope to go with. I've read over Zak Smith's optic guide but still feel uneducated.

From what I understand the first focal plane reticle shrinks and grows upon zooming and the reticle/BDC/mil-dots stay usable no matter the magnification.

So say we have a 4-16x second focal plane scope with a mil-dot reticle. Lets pretend it's zeroed at 100 yards on 4x and the mil-dots underneath stand for bullet drop at 200, 300, and 400 yards. If I now switch to 10x at 100 yards will the POA and mil-dots no longer be accurate? Would elevation need to be adjusted all shots apast 100 yards? I'm sorry if these are ridiculous questions, i'm just trying to understand.

Please explain this on a dum-dum level for me.

Thank you very much for your time.

03-29-2010, 14:36
KCabbage Remember mildots were developed for the military. First as stadia lines for artillery. Than shaped round dots then lemon drops or footballs for rifles The 2 most current ones now are stadia lines and lemon drops. Most American made scopes do not magnify the mil reticle.. When you increase magnification. You have to know what magnification power the scope is set up for the mil relation formula. If you are using this for range estimation to the target or even for shooting movers using the mil dots/lines both of these skills require alot of practice and even then we expect the students to be able to do this in an alloted time with a +-5% error factor In the beginning the USMC used stagia lines built in our binos for forward observers. Than as things progressed and we got the Unertal Scopes we got our first mil dots. It was much easier to teach Marines how to use the Mil relation formula when using the fixed 10X scope to shoot out to 1000 yds. There are also charts made up on the internet that you can find for different scopes and magnification combinations. Unless you plan to shoot to 1000 yds all the time. You can probable get away with a fixed power scope and that way all you have to do is have one set of charts for your rifle from 1oo-1000yds. In my opinion anything else can work but it just becomes fustrating and you spend more time doing math and bullet drop computations instead of just shooting. Also now adays a number of very good companies make range finders that are reasonable priced and will go out to 1000 yds. So yes if you zero at 4X mag for 100 yds and use the dots below for 2-3-400 yds ect you would need to rezero for the hight mag X

This is why you need to zero at 10X or just buy a 10X scope.

03-29-2010, 20:33
I appreciate your advice, thank you.