Australian minutes of angle
- Thread starter Leadbelly
- Start date
A minute of angle in is 1/60th of a degree, of course. I believe that the term Australian minutes is related to the calibration of Australian made rear sights. Target diagrams are printed with the minute lines corresponding to these sights, or with "British Minutes". Commonwealth sights are calibrated in "minutes of angle", usually with 1/4, but sometimes 1/3 or 1/2 minute clicks, and the sight setting can be read using the vernier scale. However, the actual shift on the target, per minute correction on the sight depends on the sight radius. The further the sights are apart, the less shift there is going to be per click. A shorter sight radius will generate a larger shift per click. It is important to know how far a click on a sight will move the point of impact. The movement of the rear sight can be measured, and with a known sight radius, calculations can be made; the results of moving the sight can also be observed and confirmed on the target.
An Aus minute is smaller than a Brit minute BUT the only way to really know what you have is to measure with a caliper the actual movement of the sight (measure at 0 and then move to 50 and measure again and divide by 50 to get the travel in .000" per minute) and then take into acount your sight radius and figure out what one of your minutes does at the target. There are many different sights around and sight radius tends to be longer now with 30 - 32" barrels and this deos have a significant effect. If you end up with a part of a thou when you divide by 50 then divide after you find travel at the distance.
