if i zero my scope at 100 yards on my 243 how much high or low would it hit at 200 to 300 yards?

Pretty much the same place as your 100 yard shots. You just need to try different ammo. My .243 shoots the same at 100 and 200 yards (don't have experience with 300) using 100 grain Remington corelokt ammo.

I agree with the rest of the crowd, this will not get you dead on, too many other variables. Here is one that really works though. 1. Bore site, or laser and fire one shot onto the target, most likely it will not be a bullseye. 2. Aim your scope back at the original target (bullseye), and hold the gun steady on the rest. While holding the gun at the target, have a friend adjust the scope while you look thru it, until the crosshairs are on the bullet hole from the first shot. 3. If you did not move your rifle, your gun is sighted in, in one shot. I always shoot one more time to make sure. Works great for black powder, saves a lot of cleaning.

zeroing in at 4 clicks on 100 yards your going to 2 clicks or half an inch on 200 and an inch low at 300

Nobody could possibly tell you that. You might get a reasonable guess for the particular load you're using from a ballistic table, but the velocity from your rifle will be different from that in the test barrel. And of course, each load (even using the exact same components, but from different lot numbers) may be off a bit, so there's no rational substitute for actually shooting your load in your rifle at those ranges to find out.

At 300 yards with 100 grain bullets it might drop 3 inches. I zero mine in at 1 inch high at 100 yards. That way it is pretty much right on at 300 plus yards.

Most major ammunition manufacturers have a web site where you can look up the ballistics chart for the exact cartridge you are shooting, just look it up.

around 2" low at 200 yd. and about 4"-5" low at 300yd. depends on your load, powder, bullet weight and also the case.

If the laws of physics haven't changed since I learned it it should drop the farther it goes.

high on 300 yards

it depends on bullet weight and powder charge. the best way is to zero it then shoot those distances and find out.