please explain how a 20 MOA rail works

[ogre6br]

I have a 20 MOA rail on my 6.5x55 and I dont really know what it's for or how to make use of it.

Can you guys please explain how the rail works in sighting in for long range etc etc

thanks
later
p

[Guest]

Patrick,
If you mount a scope on a rifle that does not have a tapered rail, you will find that your 300 yard zero will probably be about 1/2 of the way up your available elevation from absolute bottom.
If your scope has say 50moa TOTAL elevation available, this puts your 300yd zero at about 25 moa up from the bottom. Now you need 30moa to get to1000yds ( on a 308 ) so your 1000yd zero is 30+25 =55 up from bottom. You only had 50 moa available so you have run out of elevation 5 moa before 1000yds.
Now, if you fit a tapered rail with say 20moa of taper on it you pick up this on the bottom side. ie your 3oo yd zero is now at 5moa up from the bottom and your 1000yd zero is 5+ 30 =35 moa up which leaves you with 15moa above 1000yd.
This example is typical only and will vary somewhat on the rifle and the scope. But that's the basis of using a tapered rail.
Some scope have 90moa of elevation available and usually don't require a tapered rail.
Barry

[Ken L]

Further to what Barry wrote.
As you aproach the limit of elevation adjustment there is a dramatic reduction in available windage adjustment.
Now at 300 yards your windage adjustment requirements are far less than at 1000 yards and so you can't aford to sacrifice windage adjustment at the long ranges like you can at the short ones. If your windage adjustment is not centralised then the amount of elevation is reduced in the same manner so there is a case for using scope rings that have windage compensation to optimise your elevation. This becomes a necessity when you use separate front and back scope bases on a rifle as such a Remmington 700.
There is also a possibility of having an interaction between the windage and elevation adjustment when both are aproaching their limits with the possibility of damage to the scope or unexplainable changes in elevation when you adjust the windage and vice versa.

Added to this is the fact that the best resolution you get from a scope is when all the lenses are columated ( all have the very same axis) and this occurs with the adjustment in the centre of their ranges. Some people like to have this at the longest range and even if they have 90+ Moa of adjustment they still will use a matching scope rail to suit their trajectory so if they use 35 moa of adjustment from bore line to 1000 yards then they will have a 35 moa scope rail.

Then some with lots of money to spare will even go as far as using USO scopes with external adjustments to maintain this resolution over the entire range

[AlanF]

I have a 20 MOA rail on my 6.5x55 and I dont really know what it's for or how to make use of it...

The simple answer is, you don't need to do anything different than if it wasn't there - just put your scope on it and carry on as normal. The main advantage of the sloping rail is you'll be less likely to run out of elevation adjustment with your scope when you zero it at the ranges we shoot.

Alan