Inches at 100 yards, MOA, and my ballistics calc

[pontoon]

I'm looking at some scopes and trying to ensure they will go out to far enough range. One says max elevation adjustment 58 inches at 100 yards. Is this close to MOA? Like I guess an MOA is 1.047" at 100 yards?. If I use my ballistics calculator, it says I should dial 24.6 MOA up at 1000 yards for a 200 yard zero. If I change my ballistics calculator to show inches, it shows me up 258 inches. I'm not sure if this measurement corresponds to the 58 max elevation adjustment that the scope mentions. Another scope has a max of 55 MOA, so it sounds like that one would take me to 1000 and beyond given the atmospheric conditions I used for the calculation. Can anyone explain the difference between 55 inches at 100 yards of elevation adjustment vs 55 MOA of elevation adjustment and whether either or both can get my rifle to 1000 yards?

 

[FearNoWind]

One MOA is equal to 1.047 inches and most shooters simply round that down to one inch. The .047 factor amounts to an error of .47 inches at 1000 yards so it isn't really critical in making sight adjustments. An MOA scope adjustment is typically divided into 1/4 or 1/8 MOA per click segments - depending on the type and quality of the scope. 55 inches at 100 yards is, generally speaking, 58 MOA. So a 1/4 MOA scope turret adjustment requires four clicks to move 1 MOA (232 clicks for 58 MOA) while the 1/8 MOA turret requires eight clicks for 1 MOA (464 clicks for 58 MOA). My recommendations is don't be a "click counter". Just learn to read the turret markings.
I can't explain why your calculator converts 24.6 MOA to 258 inches but I'd guess it has to do with the way the data was entered.
If you don't have a 20 MOA rail on your rifle I'd suggest you get one, bed it properly and sight your rifle with a 200 yard zero with that installed. That will put your cross hairs much closer to the center of the scope when adjusting for long range. If you rely on the full extent of the scope's ability to adjust to it's full 58 MOA extent you'll be looking through the outer edges of the scopes lens which will put you into the region of less desirable resolution.

 

[pontoon]

Thanks. I think the 258 inches is the total bullet drop over 1000 yards? And that must equate to dialing up 24.6 MOA * 1.047 inches for the inches to aim up at 100 yards? Not sure at all if that is correct. I'm guessing the calculator simply can't give me the readout in inches per 100 yards and it either shows me MOA, MILS, or trajectory in the form of inches above or below the muzzle.

 

[FearNoWind]

I think you've got it. A 24.6 MOA correction at 1000 yards would suggest a trajectory geometric apex of 246 inches. It's not a perfect science and IMO 258 is close enough as a starting point. BC is often exaggerated and differs from lot to lot. Atmospheric conditions are also issues to be dealt with in coming up with numbers that work. So using 258 inches as a starting point and making careful observations of results on target will produce the best results.

 

[FEENIX]

I'm looking at some scopes and trying to ensure they will go out to far enough range. One says max elevation adjustment 58 inches at 100 yards. Is this close to MOA? Like I guess an MOA is 1.047" at 100 yards?. If I use my ballistics calculator, it says I should dial 24.6 MOA up at 1000 yards for a 200 yard zero. If I change my ballistics calculator to show inches, it shows me up 258 inches. I'm not sure if this measurement corresponds to the 58 max elevation adjustment that the scope mentions. Another scope has a max of 55 MOA, so it sounds like that one would take me to 1000 and beyond given the atmospheric conditions I used for the calculation. Can anyone explain the difference between 55 inches at 100 yards of elevation adjustment vs 55 MOA of elevation adjustment and whether either or both can get my rifle to 1000 yards?

Just want to add that most often than not, those numbers are total elevation adjustments; half of which is for "up" and the other for "down" adjustment from recommended zero. Ideally, ...

58 MOA / 2 = 29 MOA for up and 29 MOA for down adjustments and
55 MOA / 2 = 27.5 MOA for up and 27.5 MOA for down adjustments.

I totally agree with FNW, esp having 20 MOA canted base even though you have enough internal adjustment (24.6 MOA) for 1000 yards.

Best advice 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.

Cheers!