20 MOA rail a good idea? How can you tell?

[catorres1]

So I have a Tikka CTR and a new Weatherby Accuguard.

I have been using an HD5 on the Tikka, but just pulled it off to put that on the Accuguard, and a new HST on the Tikka.

I am taking a course where shooting will eventually be out to 1100 yards. So I am thinking of replacing the rail on the Tikka with a 20 MOA one, and also putting the same on the Accuguard.

But when I look at the numbers, I can't figure out how to tell if this is a good idea or not. It appears that it is possible that with a 20 MOA rail I might have to bottom out one or both scopes to get them on at 100 (where I want to have my base zero).

On the Tikka, I have mounted the HST on the rail it came with, so as soon as I recover from surgery, I can go shoot it with the stock rail and I'll know whether it will work or not. No problem.

But on the Accuguard....it seems I would have to buy a rail, mount the scope, see how many MOA I had to use to get to a 100 yard zero (either up or down), and potentially have to eat the cost of a rail that won't work for me, so that's $60 tossed away, potentially, when I have to go buy a different rail.

Am I missing something here, is there a better way to tell?

Just an example....the HD5 on my Winchester took like 9 MOA up to get to center at 100, IIRC. The Tikka took 2.

If the Accuguard took, say 5 down, lets say. I measured my HD5, it has 75 MOA top to bottom. So 5 down would mean I'd only have 27.5 left on the downside. If I put a 20 MOA rail, then I'd be only 7.5 MOA from the bottom, which I understand is a bad thing?

And if it took, say 15, I would not make a 100 yard zero at all, and even shooting a 200 yard zero, I would be somewhere near the bottom of the adjustment range most of the time.

How do you guys determine what rail to put on without just buy, trying and tossing the cash. Some of these rails are well over $100, and it seems there must be a better way I just don't know about than risking just throwing them away.

Thanks!

 

[el matador]

With 75 MOA of adjustment you will be just fine using a 20 MOA rail. You have 37.5 MOA in each direction from center, assuming everything lines up perfectly. Take off 20 for the rail, that leaves 17.5. That should be plenty, especially since you'll have to dial up about 3.5 MOA from center to achieve a 100 yard zero (1.5" of scope height plus 2" of bullet drop). So you really have 21 MOA of wiggle room with your setup, not 12.5.

 

[FEENIX]

This is probably the best advice you'll ever get from an optics SME ...

Even though the scope adjustment range may be large enough to get to 1,000 yds, you should use a 20 moa base. That's because off-axis optical aberrations that degrade resolution increase with incidence angle. You should set up your rifle so that the incidence angle is minimized for long distance shots (where resolution matters most).

Assume the base is within +/-10 moa of alignment with the rifle bore. Let's also assume your bullet drops no more than 30 moa at 1,000 yds, and you like to zero your rifle at 100 yds. With a standard base, you would need up to -40 moa of adjustment to get to 1,000 yds. That means you need a total 80 moa of adjustment.

With a 20 moa base you would need up to -20 moa to get to 1,000 yds, but up to 26 moa to get to a 100 yd zero (worse case boresight alignment in each case). That means you need a total 52 moa of adjustment. With a 20 moa base, however, the incidence angle at 1,000 yds is 20 moa less, so the image will have less blur.

Per your query below, pick one of the manufacturers (Talley, EGW, etc ...) that makes the rail for your rifle and bed it.

How do you guys determine what rail to put on without just buy, trying and tossing the cash. Some of these rails are well over $100, and it seems there must be a better way I just don't know about than risking just throwing them away.

I really don't understand what you mean by "risking just throwing them away" because that is not the case. Anyways, if you do not want to invest your money on a 20 MOA rail, you can use Burris signature zee rings with offset inserts ...

[ame]https://youtu.be/wcRAX5OLtJE?t=3[/ame]