How does a 20 MOA rail work?

[puffnstuff]

Hi guys,

Can someone tell me how a 20 MOA rail works?

It's just a 1 piece rail, I don't understand how it gives you any scope adjustment

Thanks

[Apollo]

It tilts you rifle scope 20 minutes of angle down so you get 20 more MOA of lift on your barrel for shooting at longer ranges where you need more adjustment than the scope can handle and / or keeps your scope adjustment closer to centre where it is optically far better than at it's extremities.

[brett1868]

Have to correct you on this one, it's not 20 degrees down nor angle nor barrel tilt. To be precise it's 20 Minutes Of Angle machined into the either the mount or the scope rings. 1 MOA = 1" at 100 yards, 2" at 200 yards and so on, the logic behind building elevation into the mount is to allow for longer distance shooting. Scopes have a fixed amount of elevation adjustment of which much is wasted which prevents them from obtaining Zero at extended ranges. Try this exercise, zero your rifle at 100 yards then count the clicks till you reach full down on the scope and that's the amount of wasted adjustment. Extended range shooting requires massive amounts of elevation adjustment so getting some built into the rail or rings leave more to use on the scope. Punch "Minute Of Angle" into Wikipedia for a good explanation.

[Apollo]

Sorry, it's the Flu got me brain dead....

Okay, I meant 20 Minutes Of Angle, now corrected.

Still the same story though with trying to keep your scope at or near centre adjustment for elevation at your preferred traget range. The further you go away from centre of either / both elevation and windage the worse you optics perform.

I have a 10 MOA Rail on one rifle used for 300m target and a 20 MOA Rail on another rifle which is typically used for 500m or further.

[brett1868]

Sorry, it's the Flu got me brain dead....

Okay, I meant 20 Minutes Of Angle, now corrected.

Still the same story though with trying to keep your scope at or near centre adjustment for elevation at your preferred traget range. The further you go away from centre of either / both elevation and windage the worse you optics perform.

I have a 10 MOA Rail on one rifle used for 300m target and a 20 MOA Rail on another rifle which is typically used for 500m or further.

Not quite right about keeping scope near centre of adjustment, I have 260 clicks from bottom to top and my zero @ 100 yards is 9 clicks from bottom which leaves me 251 clicks, or just over 62MOA of elevation available. What can happen on scopes is that as you approach the limits of adjustment 1 click may not be .25 MOA (in my case), indeed this can be true irrespective of where your at in the adjustment range. An important step of extended range shooting is building your scope profile and precisely measuring how far the crosshairs move over a range of clicks. I use a sheet about 6 foot high with a 1 x 1 inch grid printed on it, then from 100 yards I check where the crosshairs line up on the grid for every 4 clicks of elevation / windage. You'd be surprised at the amount of error apparent in some name brand quality scopes. From this data I build the scope profile which is then entered into my ballistics program, coupled with precise measurements of velocities and projectile B.C the software and provide very accurate firing solutions. I'm currently shooting at ranges in excess of 1500 yards and will be moving up to 2500 yards in the near future and put huge amounts of time into calibrating my scopes and gathering data.

[Apollo]

Yes, well I only use cheap March scopes so I probably need to learn a bit more for my close range 500m work to keep my accuracy at 0.1 MOA ......

I only have 60 MOA of elevation adjustment and 40 MOA of windage which is usually set at zero and use the MTR Retical to give me wind adjustments. I just like seeing bullets holes in targets near centre and keep them there.

I'm only just learning after over 50 years of shooting.

[1290]

/the rule is you can only 'correct' someone once per thread.....so your quota is spent well and truly brett1868...

going back a couple of steps, angle is measured in degree as the most common unit. Degrees are further subdivided with fractions, (old style like yd/ft/inch) as an alternative to decimals....

1 degree (of angle) contains 60 minutes (of angle)
1 minute (of angle) contains 60 seconds (of angle)

So therefore
1DoA = 60MoA = 3600SoA (60x60=3600)

The 'of Angle' part is quoted to prevent confusion with other forms of measurement using degrees(temperature), minutes and seconds (time)

A circle, being a full rotation, eg a hand going right around a clock face would rotate by 360deg or 21,600 min or 1,296,000 sec OF ANGLE.

..... so a 20 minute of angle rail will lift the rear mount by 20MoA which is 20/60= one third of a degree of angle. This accounts and allows for a trajectory with more bullet drop, generally a standard or magnum round at extended range, or even a potato chucker at a less than extended range.

For the record, referring to primary school maths, trig, using the tangent rule, one minute of angle is calculated as:

@100yd: 26.60mm = 1.05inch
@100m: 29.09mm = 1.15inch

Yes, you can almost call it one inch, but the error compounds at range.
so get shooting

[puffnstuff]

Makes sense guys, thanks.

Couldn't get my head around how it had adjustment, the obvious didn't occur to me that it just adds the 20MOA in 1 direction

I'm not shooting far enough for one anyway but good to know.

[heron]

Couldn't get my head around how it had adjustment

With the power of wishful thinking!