quote:

Originally posted by NikonUser:
Yeah, I get that. Sorry to disappoint, it's all my stuff and all errors are mine and I'm happy to be corrected.

Now, let's talk canted rail.

As we discussed earlier, a 1 inch tube will have a total adjustment range of between say 35 and 50MOA, the 30mm scopes are about double that. Some are even wider, I have an old Nikon Tactical with a 30mm tube and 80MOA adjustments. I've seen higher even.

So let's take a scope that has 45 MOA of maximum adjustment. What that means is that between the bottom adjustment to the top adjustment, there is about 45MOA of adjustment. Given a receiver and a scope mounting system that is perfect, the scope at its mechanical 0 is perfectly parallel to the bore of the barrel; both the barrel and the crosshairs are on the same target, with the difference being the distance between the bore and the middle of the scope.

At that setting, your scope now has 22.5MOA of up elevation available and 22.5MOA of down elevation.

In order to zero the scope at 100 yards, you will probably have to add a couple MOAs of up elevation. If you want to zero at 200 or 300 yards, you will need to add more up elevation, and any ballistics calculator will show you the come-ups for the various distances. To get to those distance, just dial in the come ups that you have calculated. Easy peasy.

But as you approach 22MOA of up elevation, the reticle stops moving up and doesn't got left or right worth a darn either. You've reached the maximum travel.

The problem is that before you can zero at 100, half the adjustment range is useless to you, the bottom half. Enter the canted rail. Some people think that a 20MOA canted rail will give them 20MOA more adjustment range. Not quite. What a canted rail does is it forces you to start using the bottom half of the scope's adjustment range by making the scope at mechanical zero with the perfect setup discussed above, point 20 MOA below the bore of the barrel.

To counteract that and make the crosshair and the bore be at the same point on the target. That means that when everything is parallel once again, you have 42.5 (20+22.5)MOA of up elevation and 2.5 (22-20.5)MOA of down elevation. You still have only 45MOA of elevation, but it's now divided differently between up and down.

42.5MOA of up elevation will allow you to reach out quite far with a .308 or any of the other long range loadings you might contemplate.

Canted rails comes in different angles, I've see 10, 20 and 30MOA rails. I'm sure there are more. Be careful of too much cant as it may prevent you from getting a zero at 100 yards.

Also remember when I said "perfect receiver and mounting system," it doesn't take much to misalign these things and then you end up eating some MOA range just because of imperfect hardware.

Some of you may think "why don't I just get a 20MOA ramp for all my rifles, even those I only shoot at 100 yards?" This is not a bad thought and in fact most of my rifles have a 20MOA mounting system of some kind. But they are zeroed at 300 to 1000 yards. The ones I never shoot farther than 200yards have no such device. There is no need to compress the scope's inner adjustment springs or having it push the inner tube right next to the scope's outer tube; having the scope's inner tube right at the inside of the outer tube inside diameter, may impede the windage travel.

Note: you can achieve similar results with the Burris Signature rings with their various inserts. Push the rear up and lower the front. It's more complex and you have to take the distance between the front ring and the rear ring into consideration.