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The Basics, Starting Out
20 MOA Base
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<blockquote data-quote="BallisticsGuy" data-source="post: 1511290" data-attributes="member: 96226"><p>Need? No. It's almost 100% sure that you don't "need" it for 300-400yards. 20 minutes of angle is enough to get a 7RM with mid-weight to heavy bullets out to near 1000yrds. Most good hunting scopes will have that much in them even without a canted base after being zero'd.</p><p></p><p>You use a canted base to get the elevation capability that you need to get to the distance you want. That's all. That's a thing that can only be determined based on the amount of "up" left in the scope after it's zero'd, the desired max distance of target engagement and your external ballistics with the selected load.</p><p></p><p>Start by zero'ing the rifle. Then spin the elevation turret until you run out of up and count the minutes/mils that you have left from your zero position. Now take your MV and bullet weight and other ballistics inputs and put the into your favorite ballistics calculator. See what it says you'll need to get to your max desired distance. If you don't have that much left in the optic, then a canted base is potentially on your purchase list but just as well you might need only 5 or 10MOA of cant built in. That's where you decide between things like shimming or Burris Signature Series rings or a canted base. A little bit, shim. A little more, Burris rings. A bunch, canted base. A bunch more, canted base plus Burris rings. See how that's going?</p><p></p><p>Keep in mind that some scopes; especially those on 1" tubes won't have very much total vertical adjustment range in them compared to some others so you can bone yourself by getting a base with too much cant in it. Example: 25MOA total in your scope, you zero it and have 15MOA of up left so you're 10MOA off the bottom. Add a 20MOA cant, you've just inputted 20MOA of up into the scope so you need to dial down 20MOA to retain your old zero distance but you've only got 10MOA of down left and you're now left with in a position where you will not be able to zero at the same distance as before without hitting the bottom. You'll be something like 10MOA high because there's too much up in the hardware. So, a 10MOA base would do there.</p><p></p><p>There's another factor to pay attention to. That's the issue of where scopes perform optimally optically which is right in the middle of their adjustment range. You really don't want to be zero'd all the way at the bottom of the scope's range. It leads to negative optical effects and I'm not convinced that it's not physically bad for the optic itself internally. You ideally want a setup that will get you to your max range, allow you to zero at 100yrds (my personal advice which is a separate thread) and not have the adjustment all the way at the top or bottom to accomplish either your max desired range or your desired zero range while shooting POA = POI.</p><p></p><p>I know that's a lot. You asked a much more involved question than you probably realized.</p></blockquote><p></p>
[QUOTE="BallisticsGuy, post: 1511290, member: 96226"] Need? No. It's almost 100% sure that you don't "need" it for 300-400yards. 20 minutes of angle is enough to get a 7RM with mid-weight to heavy bullets out to near 1000yrds. Most good hunting scopes will have that much in them even without a canted base after being zero'd. You use a canted base to get the elevation capability that you need to get to the distance you want. That's all. That's a thing that can only be determined based on the amount of "up" left in the scope after it's zero'd, the desired max distance of target engagement and your external ballistics with the selected load. Start by zero'ing the rifle. Then spin the elevation turret until you run out of up and count the minutes/mils that you have left from your zero position. Now take your MV and bullet weight and other ballistics inputs and put the into your favorite ballistics calculator. See what it says you'll need to get to your max desired distance. If you don't have that much left in the optic, then a canted base is potentially on your purchase list but just as well you might need only 5 or 10MOA of cant built in. That's where you decide between things like shimming or Burris Signature Series rings or a canted base. A little bit, shim. A little more, Burris rings. A bunch, canted base. A bunch more, canted base plus Burris rings. See how that's going? Keep in mind that some scopes; especially those on 1" tubes won't have very much total vertical adjustment range in them compared to some others so you can bone yourself by getting a base with too much cant in it. Example: 25MOA total in your scope, you zero it and have 15MOA of up left so you're 10MOA off the bottom. Add a 20MOA cant, you've just inputted 20MOA of up into the scope so you need to dial down 20MOA to retain your old zero distance but you've only got 10MOA of down left and you're now left with in a position where you will not be able to zero at the same distance as before without hitting the bottom. You'll be something like 10MOA high because there's too much up in the hardware. So, a 10MOA base would do there. There's another factor to pay attention to. That's the issue of where scopes perform optimally optically which is right in the middle of their adjustment range. You really don't want to be zero'd all the way at the bottom of the scope's range. It leads to negative optical effects and I'm not convinced that it's not physically bad for the optic itself internally. You ideally want a setup that will get you to your max range, allow you to zero at 100yrds (my personal advice which is a separate thread) and not have the adjustment all the way at the top or bottom to accomplish either your max desired range or your desired zero range while shooting POA = POI. I know that's a lot. You asked a much more involved question than you probably realized. [/QUOTE]
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