So, you want to shoot long range, well then I would suggest a 20MOA canted rail as a minimum. Other wise you will eat up a lot of your scopes adjustment just finding your 100 yard zero. A straight rail combined with a cheaper scope will probably max out at about 500 yards. From then on you will have to hold over your target, which is neither fun nor accurate.
Remember that the when a scope has say…40 MOA of total elevation adjustment. That is 20 MOA up and 20 MOA down from center line. Thus you will only get about 20 MOA of useful adjustment for longer range shots.
A standard 100 yard zero will use say 5 MOA of your up travel, which now leaves you with only 15 available for longer shots. And a standard .308WIN elevation correction for 1000 yards will be about 34 MOA UP, from your 100 yard zero.
So lets do some quick examples based on a .308WIN 175 Gr. SMK @ 2800 FPS:
- 0 MOA rail + 40 MOA scope – 5 MOA for your 100 yd zero. = 15 MOA left over for long range (600 yards max)
- 0 MOA rail + 80 MOA scope – 5 MOA for your 100 yd zero. = 35 MOA left over for long range (1000 yards max)
- 20 MOA rail + 40 MOA scope – 5 MOA for your 100 yd zero. = 35 MOA left over for long range (1000 yards max)
- 20 MOA rail + 80 MOA scope – 5 MOA for your 100 yd zero. = 55 MOA left over for long range (1250 yards max)
- 30 MOA rail + 40 MOA scope – 5 MOA for your 100 yd zero. = 45 MOA left over for long range (1150 yards max)
- 30 MOA rail + 80 MOA scope – 5 MOA for your 100 yd zero. = 65 MOA left over for long range (1350 yards max)
See how that works? Popping a 20 MOA rail in under a cheap scope MIGHT let you play at 1000 yards. But 30 MOA would be better. In my opinion, you want to almost max out your scope in the down direction while finding your 100 yard zero. This can be done by creating a custom rail or buying one that is really close to what you need. If you want to play the long range game: you have to get a scope with lots of elevation OR put on a canted rail OR both.
Real life example:
My NXS scope has 120 MOA of total adjustment, I bought a 40 MOA rail to try and get it really close to bottoming out for my 100 yard zero. This combination set me up with about 15 MOA left over below my 100 yard zero. Which means I get a little more than 100 MOA to play with for long range shooting. Now, why is this important to me? Because to shoot 1 mile or 1760 yards, I need about 113 MOA of correction. Thus, I can almost zero my scope for 1 mile shots.
With that kind of flexibility, I have no idea why anyone would ever want a straight rail on their rifle. 20 MOA is minimum in my books.
Here is me shooting at 1525 yards, I had a few hits, but you can’t really tell from the shooting location:
Final note: I am a firm believer in the idea of K.I.S.S. or Keep It Simple Stupid. To that end, I like to have as few components as possible in any system. Thus I do not like the idea of shimming a scope or rail to get the desired elevation. Shimming or the use of inserts just adds another set of variables that you may have to watch, or could induce errors into your shooting system. Correct torque and loctite become even more important when you add variables like this.
So I say “why bother?” Just buy a solid scope rail that is already canted the amount you need right from the start. All this takes is a little planning and some math and you will have a solid setup that cannot fail you…right from the start.
There are plenty of people who use shims and the likes to make long range shooting possible within the equipment they own. And I am sure they are quite successful at times. But I can tell you it is also these people on the shooting line who are always asking for you to spot their shots, because they can’t seem to figure out where they are shooting. Faulty equipment is not what you want in the world of long range shooting. This is a sport in which you are trying to eliminate or control as many variables as possible, so why would you create another one?