HKFan-- That is why you learn to se the Mil Dot system. Once sighted in you do not need to resight in for a greater distance,you use the Mil dots. Now that is barring going from 100 yards to 1000 yards. But any rifle you shoot at 100 yards would not be used at 1000 yards any how. But you knew that..
Mil-dot......is a ranging increment, meant to determine an unknown range for a target... not compensate for a shot. A ballistic reticle WOULD do what you are saying.. however they are tailored for 1 round, on 1 rifle, for 1 altitude and so on, generally custom ordered (if you want them done right) for scopes that cost $$.
Yes Mil-Dot can be used to hold over or wind or moving, however if the first shot counts.. as they were designed for combat, or hunting that trophy animal.. it is generally understand to make your calculation, adjust your knobs, and take the shot, if the first shot misses, is when corrections can be quickly made using the mil's.
Also when using them, it can depend on what power your scope is set it, and what focal plane you are using inside the reticle. MOST scopes are Second Focal plane, so your measurements with your Mils will be different at 5 power than at 12 power. First Focal Place scopes the reticles adjust with the power of magnification, so you're measurements stay consistent.
Mil-dot hash's or MRAD's are only to meant to measure a target to figure out the unknown distance to it, you then can HOLD OVER to compensate for the shot, or adjust your turret. Generally speaking most people including myself will do the calculation, adjust the elevation turret, and then use a hold over to correct for windage as wind changes constantly, unless paper printing I rarely adjust my windage turret.
Problem with cheaper scopes even have mixed and matched reticles to turrets.... you may have a Mil-dot or MRAD reticle, but MOA adjustment turrets, or vice versa. Makes things difficult.
A rifle for shooting 100 yards wont shoot at 1000? really? I have a Kimber 8400 Advanced tactical with a Vortex Razor 5-20x scope that has no problem keeping a 100 yard zero and has no problem dialing up to 1000. The Vortex Razor and other scopes like it are designed to have the adjustment, along with the 20MOA base on my rifle. This is why proper tracking is important, if your scopes tracking isn't correct, you can do the math right, however when you make those turret turns from 100 to your 535yard target, if your scope isn't made well and the tracking isn't precise, well it won't be accurate.
On that scope, you take your turret caps off when zeroing the rifle, they free spool in this mode to get an exact zero, then re-install the caps at the 0 mark. If I want to shoot 100 yards I rotate my turret back to the 0 stop... if I range a target at 200 yards, sure a hold over will suffice... or I can click up .6 MRADs and be dead on, and so on.
NOW, all that being said is probably ill-relevant to the OP, however there are big differences in scope quality and mechanics that people actually using a rifle to its capability will pay for. I shoot handguns at 100 yards with iron sights... anything from my .45's to my 5.7. 100 yards you can shoot well with just about any scope/red-dot, irons, ect.
Not everyone needs to go out and drop $2000+ on a scope and $150+ on rings... however people into shooting long ranges accurately, or competition, hunting, you name it... I think its wise to invest in something decent.
A $150 Nikon or Leupold VX-1 will be worlds better than Simmons, Tasco, ect. Don't get me wrong I have an old .30-30 with a Tasco, and a few Simmons on a few .22lr's, however I still by the side the scope should cost what the rifle did.