The following has been reprinted with the permission of ExpertReloader. We invite everyone to visit them and view their informative tips on reloading shotshells or better yet get a copy of Mr. Rozek's "MEC Shotshell Reloading Secrets Guide"

By: Jonathan Rozek
(Shotgunworld Note: Please visit this section often for future articles from Mr. Rozek)

How to set up your reloader for any combination of hull, wad, shot, powder, and primer:

1. Decide which hull type you will reload, as discussed elsewhere.
2. Get hold of reloading data from several manufacturers. You can either get these thin pamphlets from the place you buy powder, or by going to the manufacturers' websites.
3. Look up the hull type you have, in the gauge you are shooting. For instance, manufacturers may refer to Remington Premier STS as "Remington premier." Determine the most widely used powders from the recipes shown. Write them down. Notice that some powders are best suited for 12 gauge, and others are made for smaller gauges.
4. Buy one of the powders from your list. Your supplier doesn't have what you want? Watch out! Don't just buy what's around. You've got to buy one that was listed for the hull type you're reloading. They are not interchangeable. When you're messing with 5-7 tons per square inch of pressure, six inches from your eyeballs when the gun goes off, you want to know that someone else has used that recipe successfully before.
5. Buy the wads and primers listed for the hull and powder you have selected. You will have a bit of selection, depending on what weight of shot and what muzzle velocity you pick. Go first with a shot weight that has the most recipes. A good standard velocity is 1,200 feet per second or thereabout for 12 gauge. The most popular shot weight and velocity is generally the one with the most recipes. You can shoot heavier or lighter loads later, when you're used to the mainstream combinations.
6. Determine from the powder manufacturer's reloading manual (usually available free where you bought the powder) how many grains of powder you should use for your combination of gauge, hull, powder, wad, shot and desired muzzle velocity.
7. Look up which bushing you should use from MEC chart. You need to know the right bushing is only an approximation! More on that in a minute.
8. Put only powder in the reloader. It makes the repetitive process of measuring and adjusting the powder drop a little easier--you don't have to worry about catching shot.
9. Get or borrow a scale. A good, relatively inexpensive one is the RCBS Model 10.10 Reloading Scale, readily available.
10. Set up your scale and zero it, according to the scale instructions
11. Set scale to desired powder charge, so when you pour the powder into its tray, the scale will read zero. This is much easier than trying to remember "was that 16.8 grains, or 18.6 grains?"
12. Unhook the primer drop spring so you don't have to worry about primers dropping as you calibrate the reloader.
13. Put empty shells under the reprime/powder station and the wad/shot station. Do not insert a wad.
14. Drop powder into the spent shell. Take the shot that dropped into a shell and pour it back into the shot container.
15. Pour powder into the scale pan and see if you are in the ballpark for the number of grains you should be using.
16. If you are light or heavy, then swap out a new powder bushing. (See the MEC manual for that.) You can file out a bushing to make it a bit larger, or use nail polish to make the chamber smaller. When you have the right weight, the scale should zero out, because you had earlier set it to read zero at this weight.
17. Retest the new setting on at least two more shells. I say at least two, because the first powder drop will be inaccurate after you've just changed the powder bushing. You've jiggled it, and probably compacted it. Maybe not, but be sure by getting two or three readings before deciding you're done.
18. This stuff is a pain. But once it's set, that is a real incentive to leave the recipe alone unless you're having problems with it.  

Do you really have to weigh your own powder?  Why not just follow the MEC manual for correct bushing size?
There are too many variables involved in powder metering for a given bushing or handbook setting to be precise enough. For instance:

• Humidity
• How densely packed the powder is (this will vary depending on how much it is shaken, and whether the bottle is full or almost empty)
• Manufacturing variations
• How much you jiggle the reloader when using it, etc.

If you're just out to have a good time and not shoot a personal best, then you may be able to use the bushing chart. But if you are serious about hitting what you shoot at, you need to know what exactly you're shooting. So spend a few minutes doing the weighing, and you can then leave it alone until you change shell types, or powder, etc.