So... Help me out with some calculations

[LynnJr]

Me too.
If your 20 MOA base won't let you zero at 100 yards you could always shim it.

I know that is like cussing in church to some but its free and it works.

[JMP]

So we are using the same terms... UP elevation (to you) means scope elevator travel DOWN and resulting bullet travel UP right?

That being the case, a 20moa canted mount eats up elevation DOWN travel.
But, the 36moa scope case is interesting BECAUSE of the 5 moa UP elevation lost to the zeroing, also puts the gun about able to absorb 20moa of rail cant.

No, we are talking the same thing. Indeed the 20 MOA base eats elevation down. It's just the opposite of a typical case. Normally, scopes have ample room to adjust for a 20 MOA base, but in this case, the more elevation eaten UP by zeroing, the better chances of allowing for a 20 MOA base. So typically, it's ideal to mount the scope as low as possible, but, as I suggested in my absurd example, the higher the scope is mounted, the more UP MOA are eaten. In a perfect world, he may have 23 MOA down to accommodate the 20 MOA mount, but it is dependent on the scope. It could work, but I'd wager that it does not zero at 100 yards. If it does zero to 100 yards, then he'll be zeroed too close to the lower extrema, limiting horizontal adjustments.

I'd go with a 0 MOA base and use a rear ring insert or shim to get a little more elevation up. You don't need that much elevation at 700 yards. Of course, a 300 yard zero wouldn't be a bad thing as it would provide about 3 additional arcminutes for elevation, which isn't a bad hold under for 100 yards, and .308 shooting is typically 400-900 yards. Of course, I don't see getting to 900 yards with 36 arcminutes for total elevation travel.

[JMP]

the better route would have been burris signature rings with posi-line inserts. you can adjust the to get any odd amount of incline you want. Id use them all the time in my shop. run the scope down to its "bottom", turne it up about 10 clicks, then set it on the rings while viewing a columnator boresight. swap posilign inserts till the x hair is centered on the columnator. done.

20 moa was an arbitrary figure chosen beacuse it can be represented by a .50" rise over a 5" run. easy to program. it's a third of a degree.

Farrel does make bases in 5, 10, 20 and 30 moa iirc.

Methinks there are some zeros missing here.

He's off by a factor of 36. He meant 0.5" and 5 yards, assuming sMOA and not proper arcminutes.

[CRTguns]

Methinks there are some zeros missing here.

meant .025" over 5"

so sorry. wont happen again.

[JMP]

20 moa was an arbitrary figure chosen beacuse it can be represented by a .50" rise over a 5" run. easy to program. it's a third of a degree.

Farrel does make bases in 5, 10, 20 and 30 moa iirc.

meant .025" over 5"

so sorry. wont happen again.

I was unaware of that fact. However, can you clarify?

I have:
ArcTan(.025/5) * 180 / Pi = 0.286477 degrees that is 17.2 arcminutes, not 20.

Where am I going wrong? Admittedly, I am not good with numbers.

[ar15barrels]

meant .025" over 5"

I use a 0.029" differential of gauge blocks under a 5" sine bar when I'm trying to mill 20moa into a base.
I'm not good with the math on a calculator, but If I draw it up in autocad, that's the dimension I come up with to get 1/3 of a degree of rail cant.

[JMP]

I use a 0.029" differential of gauge blocks under a 5" sine bar when I'm trying to mill 20moa into a base.
I'm not good with the math on a calculator, but If I draw it up in autocad, that's the dimension I come up with to get 1/3 of a degree of rail cant.

I come to the same conclusion with a few calculations.

ArcTan(0.028"/5")*180/Pi = 0.32085 degrees = 19.25 arcminutes
ArcTan(0.029"/5")*180/Pi = 0.33231 degrees = 19.94 arcminutes
ArcTan(0.030"/5")*180/Pi = 0.34377 degrees = 20.63 arcminutes

[ar15barrels]

I come to the same conclusion with a few calculations.

ArcTan(0.028"/5")*180/Pi = 0.32085 degrees = 19.25 arcminutes
ArcTan(0.029"/5")*180/Pi = 0.33231 degrees = 19.94 arcminutes
ArcTan(0.030"/5")*180/Pi = 0.34377 degrees = 20.63 arcminutes

The more accurate number I came up with is 0.0291" over 5", but I don't worry about tenths of thousandths on a milling machine...

[winxp_man]

To the Op if you have not done it yet. Might want to return that scope back to where you bought it from and check out a SWFA 10X scope. Might be that you will end up going with the SWFA for a while before upgrading. The scopes are bullet proof almost.

[JMP]

The more accurate number I came up with is 0.0291" over 5", but I don't worry about tenths of thousandths on a milling machine...

Try 0.0290891490547767", if you want real precision.

[CRTguns]

your calculations are impressive... and are important if your landing on the moon.

measure most "20 moa" bases. They are not 20.0 moa. they vary a ton. "20" as a figure is a number pulled out ofd the air. And few mfgs stick to it. I've found brands of "moa" base that ameasure all over the place. None of them are not truly 20.000000moa. So what.

Few manufacturing shops are capable of holding better than +/- .005" for most parts. That kind of tolerance will produce a base within 4 moa of desired? Again... it's not a critical angle. Most brands see it his way and just fudge it into nice round whole numbers....then label it 20, because it's become a fad.

[JMP]

your calculations are impressive... and are important if your landing on the moon.

measure most "20 moa" bases. They are not 20.0 moa. they vary a ton. "20" as a figure is a number pulled out ofd the air. And few mfgs stick to it. I've found brands of "moa" base that ameasure all over the place. None of them are not truly 20.000000moa. So what.

Few manufacturing shops are capable of holding better than +/- .005" for most parts. That kind of tolerance will produce a base within 4 moa of desired? Again... it's not a critical angle. Most brands see it his way and just fudge it into nice round whole numbers....then label it 20, because it's become a fad.

20 MOAs are the most common base, but it is not universal. Accuracy International , for example, uses an 18 MOA mount.

[billetmann]

Use the cheap scope to dial in at 100 yards and when your ready to reach out to big distances then get your new scope that's equipped for such distance.

[hambam105]

Remington 700P-26in. Badger 20 MOA Base. M3 LR, 10X MK4 rings. Federal 175 grain.

Units in MOA.

Zero at 100 yards, 55/75 deg.
<45 deg+1
76/95 deg. -1
>95 deg. -1

700 yards, 22 MOA <45 deg.
21 MOA 55/75 deg
20 MOA 75/94 deg
19 MOA >95 deg.

1000 yards, 42 MOA <45deg.
40 MOA 55/75 deg.
38 MOA 76/94 deg.
36 MOA >95 deg.

Note: -1 is lowest setting. I use mildots to strike .75 inch sized targets from 10 yards to 99 yards. Wind is not a variable <50 yards.

[hambam105]

So if the OP would zero his rifle at 700 yards today, >95 degree, July heat, and then waltzed out on the same Range this January, <45 degree, cold morning, there would be a 3 MOA difference.

A 3 MOA difference at 700 yards is 21 inch change of vertical impact. In this example it would be 21 inches low.

No change is shooter's ability with same ammunition a given.