by bladeracer » 05 Jan 2022, 12:45 pm
Something to remember about minutes is that there is no fixed size, a minute is a different size depending on distance. You can look at an object in the distance and estimate its size reasonably accurately. That goat is about two-foot-six at the shoulder, that Coke can is about 150mm tall, that fence post is about as wide as my hand, and so on, its distance is irrelevant. But you can't do the same with minutes unless you know the distance. Even through binoculars you have a rough idea of the size of things, whether they a meter away or a thousand meters away.
Optics generally give you some sort of scale that relates the view to the distance, based on the magnification. If your scope has a reticle that is .25MoA thick at 18-power, you can use that to approximately measure things, without knowing the distance. That fence post is about four reticles wide, so it's a minute wide. If you know the distance then you can calculate the actual width. If you know the distance is 400m, then you know the post is about 120mm wide. Likewise, if you set up a 200mm gong in a paddock, you can compare its size to your reticle. If the gong is about six reticles wide, or 1.5-minutes, you can calculate that the distance is about 460m. Scopes nowadays have additional stadia in the reticle to make this easier. Binoculars don't have any reticle, but if you know how wide the field-of-view is, you can use that to approximately sizes and distances. My 7x50's for example have a FoV of 15.7m at 100m, so if I see a large deer I can roughly tell the range by comparing its size to the FoV. Our eye can generally bisect a circle fairly accurately, so you only need compare your target to the distance from the centre of the view to the edge, or about 7.85m@100m. If you are looking at a deer that you figure is about two-meters wide, and it covers about a quarter of your half-view, you know it's about 400m away.
With a second-focal-plane scope you can further complicate the above by using your zoom to change your reticle dimensions. Your reticle dimensions will be twice as big at half the zoom, four-times at a quarter zoom, and so on.
Understanding how minutes relate to dimensions is certainly important. But if you are shooting at a target, and your bullets are hitting some distance to the left in your scope, you don't need to know the distance or the size. You only need to estimate how many minutes you are off, and adjust by that many minutes - the distance is irrelevant. My reticle is a duplex with bullet drop stadia. The duplex reticle is 3MoA radius, and I can use that to very quickly estimate how far I missed by, or how much wind I need to allow for.
Likewise with my BDC holdovers, which are at 1.7, 4.4, 7.6, 11.4, and 15.4MoA (top of the duplex) vertically below the reticle (all my scopes are the same so I have memorised these five numbers by now). These are supposed to follow a "standard" 55gn .223 load, but don't, at least not for precise shooting.
Relating this back to what I mentioned earlier, if I need to holdover 30-minutes, my reticle only measures to 15.4-minutes, so I can try to hold twice as far down the post...or I can wind the zoom back to 9-power and my reticle magically transforms to a 30.8MoA holdover.
Other scopes use grids or dots at minute or millirad intervals.
It all sounds immensely complex, but once you spend some time playing with it it will become second nature.
Try shooting a scope box test to get a feel for it. Set up a decently large target page, say two A3 pages at 50m. Zero your rifle to an aiming mark in the centre - and reset your turrets to zero, or note your turret positions. Then wind your scope up 10-minutes (40 clicks) and right 10-minutes. Shoot a group while holding the same aim point in the centre of the page. Then go 20-minutes down and 20-minutes left. Shoot another group. Then come up 20-minutes and shoot a group. Then 20-minutes down and right, shoot a group. Then up and left 10-minutes. Your final group should be dead on the centre again, if the turrets track accurately. The other four groups should be 145mm vertically and horizontally (not diagonally) from your centre group if the turrets are true quarter-minute clicks.
Remember, the "up" and "rt" on the turrets refer to the direction you want your bullets to move across the paper, not the direction the reticle moves. If your group is to the right of your point of aim, you want your bullets to "move" to the left, so you turn the turret "left". When your zero the rifle you want to shoot a group, then hold the rifle still and adjust the turrets to move the reticle to your group, in this case you will turn the turrets in the opposite direction to their markings.
Practice Strict Gun Control - Precision Counts!