Jessegreenwood: No....your powder selection(Red Dot) will work just fine. All you need do to load the lighter 1 1/8 oz loads, is go to either a WAA12 wad, or the Claybuster equivalent: CB1118-12. Good choice, for either Remington, or Winchester hulls. For Federal or Cheddite(Challenger) hulls: Federal 12S3, works well for 1 1/8 oz payloads. Claybuster equivalent: CB2118-12.
And yes....the WAA12F114 wad is very suitable for use in 2 3/4" shotshell loads. Just not the best choice, for 1 1/8 oz.
As a matter of interest, you don't have to limit yourself to Red Dot. There are any number of powders which will work just as well. Hodgdon Clays for example, is an excellent powder for light loads.
Should you wish to load 1 1/4 oz loads...as well as 1 1/8 oz, Alliant Unique, or its near-twin Hodgdon Universal, would be good powders to select, too. Both very versatile, for a variety of reloading tasks.
Unique is also a longtime favourite for reduced-velocity, lead bullet loads in many rifle cartridges. Including: .30-06, etc. Worth checking out.
The choices are pretty broad. So don't think you have to limit yourself. As you become more knowledgeable about shotshell reloading, a lot of this will become much clearer. For now, scrounge up as many hulls as you can and simply get a handle on the process.
Also: Be sure to ask plenty of questions. That is how you learn. There are some very knowledgeable folks on this forum, who can help.
By the way, your Mec 600 is an excellent shotshell reloading press. Versatile and easily adjustable. Replacement parts are also readily available, if needed.
Including: 6-point crimp starters.
A good source for Mec parts: Hummason. Based near Ancaster, Ontario. But will ship.
Al
ps: For many, many years before the introduction of steel shot for waterfowl hunting, THE standard 2 3/4" shotshell load, was 1 1/4 oz of #4 lead shot, at 1330 fps. Still a good choice, under many hunting conditions.