Need Help With MOA????

[dave@aDave]

FWIW & FYI: 3,000 ft/sec = 5,498,181.82 furlongs/fortnight

 

[GSPV]

How about a Firkin for the mass unit so that we get the FFF system.

Furlongs, Firkins, Fortnights.

I got started on this way back in the day because there was a parameter in the VMS operating system, which was near and dear to my heart, that was in millifortnights (about 1.2 seconds).

 

[BenPerfected]

Yawn. Mills brothers. Anybody here old enough to remember them?

I remember them, but this was my Fathers music.

 

[natdscott]

Let me take a crack at the geometry. If you drew a big circle with a radius of 100 yards, it would have a circumference of 2 *pi * 100 yards or 6.283 * 100 yards = 628.3 yards. One degree of arc then is 628.3 yards/360 degrees = 1.745 yards. This is 62.82 inches. One minute of arc is 1/60 of a degree so 1 MOA = 62.82/60 = 1.047 inches.

I'ma simplify this.

( tan(0.01667) * (Range in Yards) ) X 36 inches per yard = 1 MOA at that distance, in inches


-Nate

 

[Ned Ludd]

FWIW & FYI: 3,000 ft/sec = 5,498,181.82 furlongs/fortnight

Nice. Hmmm, now if I can only get my LabRadar to output these units...

 

[Bart B.]

https://www.nssf.org/shooting/minute-angle-moa/

USA NRA target rings are mostly inch spaced.

Everyone used inches per hundred yards until hand held calculators with trig functions came on the market in the 1960's. To be reasonably exact, use this.

1.04719753642832854694747069666400334739860873986429
830552235157457471965151538005004775737357536725837.. inches per yard.

For simplicity, use 1 inch per hundred yards.

No optical sight's movement claim is exact, their lenses have focal length tolerances so up to a few percent error is normal. That few percent spread in the first image plain size the very repeatable mechanical angular adjustments center on causes the errors.

Exact is best calculated with mechanical sights knowing their sight radius and lead screw pitch.

 

[ED3]

https://www.nssf.org/shooting/minute-angle-moa/

USA NRA target rings are mostly inch spaced.

Everyone used inches per hundred yards until hand held calculators with trig functions came on the market in the 1960's. To be reasonably exact, use this.

1.04719753642832854694747069666400334739860873986429
830552235157457471965151538005004775737357536725837.. inches per yard.

For simplicity, use 1 inch per hundred yards.

No optical sight's movement claim is exact, their lenses have focal length tolerances. Exact is best calculated with mechanical sights knowing their sight radius and lead screw pitch.

It's actually:
1.04719753642832854694747069666400334739860873986429
830552235157457471965151538005004775737357536725837 inches per 100 yards...

and you can get the number on a calculator simply by: pi/ 3

 

[Bart B.]

and you can get the number on a calculator simply by: pi/ 3

To 102 visible decimal places?

 

[ED3]

To 102 visible decimal places?

Good point

 

[Bart B.]

Over a century ago, metallic aperture target sights has 40 tpi lead screws. 4 clicks on the rear sight knob moved the aperture one third of the .025" thread spacing. With the standard sight radius of 30 inches, that's exactly 1/3600th of the sight radius. 3600 inches is 100 yards.

External adjusted target scopes had mounts spaced 7.2 inches. Their adjustments were also 40 tpi threaded but had 50 clicks per turn. 4 clicks moved the adjustment .002" that's 1/3600ths of 7.2 inches.

Use what you want.

 

[ED3]

you forgot to factor in the rotation of the Earth

. . .or rain drops. . .

 

[Bart B.]

FWIW & FYI: 3,000 ft/sec = 5,498,181.82 furlongs/fortnight

FWIW, the speed unit on water, knot, isn't a convulated abbreviation of nautical to "naut." It referred to knots in a sea anchored rope tied about 50 feet apart with a 30 second sand glass as first used by the Portuguese in the middle ages.

 

[alf]

I just dial to my impact and shoot again.......

 

[Webster]

On the Grendel forum a guys was shooting inch and half groups at 200yds and everyone kept saying he was shooting 2 MOA at 200yds but as I understand it...that would be a 4" group, not 1.5". Plus there was more than one saying it...so it had me thinking I was wrong.

But...they also claim you only need a 12" barrel on a 6.5 Grendel when shooting out to 600yds! I fought a long hard battle over that...they ended up calling me names because I said they would get better velocity from a 20". They really didn't like it when I told them they were wasting powder and loosing a lot of velocity on a cartridge that needed all the help it could get...

But that' another thread!

Thanks guys...you successfully gave me a headache with all the math/arithmetic...

Sometimes it's best to just ignore some EXPERTS. Feel comfortable that you understand it.