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Canted bases, revisited

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/27/2010 at 13:06
Rancid Coolaid View Drop Down
Optics Jedi Master
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Joined: January/19/2005
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Since I highly recommend canted bases on many tactical setups (long range and otherwise), I get many questions regarding what the rail actually accomplishes, most usually, something like : "Does a 20MOA base and a 50MOA scope give me 70MOA of adjustment?"

In short, no, and here's why:

A scope with 50MOA of elevation travel, when the reticle is centered, has 25MOA up and 25MOA down.  A 20MOA base, if the reticle is centered and the claimed 50MOA is actually 50, gives you 25MOA down + 20MOA from the rail= 45MOA.  There is nothing the rail can do to overcome the scope's elevation range limits.  You do not "gain"  an additional 20MOA with a rail, you simply reclaim 20 of the 25MOA that would be wasted - since you - once zeroed - never dope a reticle up, within certain limitations - most notably, a zero other than 100-200 yards.

With a 100-yard zero, a shot at longer range has you adjusted the reticle down, to compensate for the rainbow of the round.  With a 100-yard zero, no shot you take will require a dope change up, so any MOA-adjustment up is lost in terms of shooting utility.

All this "assumes" 2 things:

1.  You are dead-nuts centered in the elevation range when rounds are on target at whatever your zero - with a 0MOA rail, meaning you have 25MOA up and 25MOA down on a 50MOA elevation adjustment range
2.  Your claimed 50MOA is actually 50MOA.

Most of the time, one or both of these is not true.

Whether on tactical gun or not, a like canted rails (scope permitting) because it allows for more doping options, should I need them.  Once a scope is zeroed at some relatively close range, any "up" elevation remaining is wasted. Mostly.

Clear as mud?

I'll try to scrounge some pictures to demonstrate the effect.


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/14/2010 at 10:14
opeagle View Drop Down
Optics Apprentice
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Joined: November/22/2009
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 Pics are always nice.

 Thanks for the thoughts.  I am in the middle of this debate right now and your guidance is most appreciated.
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