Emcom:
A mil is a mil, a moa is a moa. I stayed away from FFP/SFP. Regardless of scope the recital has to reflect mil/moa to be a mil/moa scope. When one buys a scope, the directions tell you what power the scope needs to be set to, to for the reference dots to reflect mil/moa's. (not all are on the max power).
Mils are use to measure distance, but I wouldn't go so far to say that is their primary purpose.
I've used and taught Mils before they started showing up on rife scopes. Mainly in Machine Guns. The T&E on most MGs are in mils, and you adjust in mils. For example using a range card, you mark possible target points. You lay the gun at one point, and mark that as zero, then each target point is so many mils right, left, up, or down from your zero. In doing that, you can engage targets you cant see such as at night.
Horizontal distance can also be measured in mils using the index finger. For example, the average index finger is 50 mils. So in plotting targets for the range card, for example, you can use the extended finger to see that from the ref. point, target X is 1 and 1/3 finger width, or 75 mils right.
Or, if the spotter says "shift right 100 mils, you can simply hold your finger out to the right side of the sight, holding the hand still move the sight to the right of the finger, (move is 50 mis) do this a second time, and you shifted the gun 100 mils.
1 mil is 1 yard at 1000 yards so 50 mils is 50 yards at 1000 yards
Granted shift 50 yards isn't normally called for when hunting, but the principle is the same.
Knowing 1 mil is 1 yard at 1000, we can assume that 1 mil is 18 inches at 500 yards. So if we are shooting a target at 500 yards and the wind is a fv value 15 MPH wind, we check our data card and release we need a horizontal hold of 1.4 mils. to correct for this wind, we simply use the horizontal scale on the recital to hold off.
Regardless, the scope power has to be set to reflect true mils (or moa on moa scopes)
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KCUB:
Question about dialing in. When finished do you return to some pre-established point, say dialed in at 100 yards?
For me, depends.
When hunting, no. When I sight in the scope I zero the elevation and windage knobs. The scope dial is marked 1, 2, 3, etc. So on MOA scope the 1 would be 1 MOA, from 0, with normally 1/4 clicks in between. The Mil scope also is measured in 1, 2, 3, etc. but it is mils. The Mil scope normally has .1 mil clicks.
So if your scope is set on one number, and your target range calls for a another number, you move to that number. Let say you need to come up from zero 5.25 MOA. Regardless of where your scope is set. You move it to 5 and add one more click to get the .25. Same with mils.
HOWEVER. In rifle shooting, I shot iron sights. On the M1 or M14 you can get your zero and set the elevation dial to that zero. So when the 2 on the dial is lines up with the mark on the sight base, you are sighted in for 200 yards and can set your sights to any mark without counting. But the ammo has be match the sights.
I use the score or data book. I know how many clicks up for each range for the ammo I'm using because its written down. After firing on each yard line, I put my sight back into the bottom, then when I get to the next yard line I count up the clicks needed for that distance. Its a habit I developed a long time ago because when I first started shooting, I forgot, and ended up adding my elevation twice.
To see the witness marks on my M1/M14 sights, I have to put on my reading glasses. That's a bit more flopping around then want when in position so I just count clicks.