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Incline Base and Ballistic Reticle

 
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  #1  
Old 01-21-2008, 03:09 PM
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Join Date: Jun 2004
Location: Tylertown, MS
Posts: 16
Incline Base and Ballistic Reticle

Hello folks, well I have searched and read and spent too much time trying to find the answers on this. Having read all about mildot, moa, using holdovers and holdunders. Just getting a little too much time here.

My question is on something like a Leupold VX3 4.5-14x50 scope with the Boone & Crockett reticle for shooting holdovers long distance how would a 25 MOA incline base affect this. I understand that using a incline base does for you on 100yd zero and dialing up to get out to say 1000yd. But if you have something like a 300 yard zero on a big magnum rifle what effect is that going to have on your holdover points then. Some might say it is not needed but having come into a rifle with one installed I would like to know.

Now that Leupold has come out with there new RX-IV B&C rangefinder that is suppose to show you where to aim with depending on which one of the 7 range charts it has actived and the angle indication. I know that the incline or cant base would have to come into a factor with the scope and something just seems like it would be a miss on out there. Thanks for all you folks in the know's help
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  #2  
Old 01-21-2008, 04:31 PM
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Join Date: Jun 2007
Posts: 213
Your holdover points will always be the same relative ANGULAR elevation over your set zero -- the thing is, the bullet obviously starts dropping more as your shots get farther out.

Basically you'll want to found out what your elevation points are in MOA (or MILs) over your center cross hair. If you can't find the data in documentation, you could figure this out with a properly marked target set up at 100 yards (1 MOA = 1.047" at 100 yards). You can just look at your reticle and see what hash marks it lines up with to figure out how many MOA of elevation each mark gives you

Then you'll need to use some ballistics software (there are some free online ones) to figure out your drop chart in MOA, relative to your zero. For example, your drop chart for a .300 RUM might look like this (Distance in Yards : MOA of drop):

300 : 0
400 : 2.0
500 : 4.25
600 : 6.5
700 : 9.25
800 : 12.25
900 : 15.5
1000 : 19.25

So if that's your drop chart, and you figure out that your reticle elevation marks art 4, 8, and 12 MOA -- then the ticks would correspond to a bit under 500 yards, somewhere between 600-700 yards, and just under 800 yards. Of course, if you do your drop chart in increments of 5 yards or something, you can get much more precise drop values for your scope markings.

Anyway, I think the important concept is that the hash marks will always give you the same angular elevation over your zero -- so just think in terms of MOA of elevation over your zero.

Hope that helps.
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  #3  
Old 01-22-2008, 01:37 AM
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Join Date: Jun 2007
Posts: 213
Leupy B&C Reticle

gtcontender,

I got home and checked my Load Base 2 software (Ballistics Software from Patagonia Ballistics) -- and it has your reticle.

I plugged in the numbers for a .300 RUM shooting 210 Bergers at 3000 FPS, and it provided the following --



Hope that helps. If you want, give me a specific bullet & muzzle velocity and I'll plug it in for you.

Matt
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  #4  
Old 01-22-2008, 11:53 PM
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Join Date: Jun 2004
Location: Tylertown, MS
Posts: 16
Matt

Sure appreciate the info. I was under basically the same impression from all my reading and such. What I was shooting was 338 cal. 250 grain SMK at 2940fps chrono 10 feet from the muzzle. When I first shot it to check group and speeds it ended up being 2 inch high at 100 just because that was kinda where it ended up at on checking loads I left it there. Running some ballistics software on the net. That ended up showing about 240 sight in. I had a mildot scope on it and thought I would use the mildots as holdover points, 1 mil came in right at 400 yards. Well I finally got a chance to shoot it at 400 yard range and we was surprise when I shot with the 1 mil dot and hit extremely high, in fact it hit right on the crosshair center. So at that point I started second guessing everything about the 25MOA incline base must have something to do with throwing off the hold overs. I have to do some more shooting to check it some more when time premits. I am sure I was doing something wrong here. If you are able to run some data on the above sure would appreciate it would give me a little better ideal with the new VX3 scope. Thank Greg
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