Take the .223 for example. I can buy the two die set for a reasonable amount of money, but then I see they offer a competition two die set for considerably more money. Is there that much difference in accuracy between the two to justify the cost?
The competition dies often have micrometer adjustments and windows to feed into- not more accurate, just a bit easier to use.
Further they offer a small base die set for recommended for autos but not bolt actions.... Is this a necessity for something like an AR-15?
Yes and no. If you use once fired military brass (usually fired out of a machinegun with very loose chamber tolerances) then you absolutely need one. If you are using commercial brass, you won't have many problems. An AR-15 isn't prone to out of battery firing like a worn or out-of-spec M1 or M1a is. If you are just loading for the AR-15 in .223 I would get the small base sizing die- it will do no harm.
How about the carbide full length sizer that eliminates the need for case lubrication. Is this something that every reloader should have? How about a neck sizer die?
Yes, yes, and maybe. Carbide dies are the only way to go for straight walled cases. Necksizer- only if you are shooting a bolt action with an aftermarket barrel and tightly (and very squarely) cut chamber.
Then there is the issue of having a case trimmer... The RCBS model is not cheap. I assume this is a very necessary tool, yes?
Avoid the RCBS ( I really hate mine and it doesn't cut very square), its not the best for the price. Lyman is better, Forster is far better, a Lee cutter will even be better than the RCBS on standard cartridges for a tiny fraction of the cost and is much easier to use.
Is the RCBS precision mic that measures the chamber headspace and bullet seating depth a necessity also?
A
cartridge headspace guage is an absolute necessity with an AR-15, M1, M1A. Without it, you are only fumbling around in the dark. RCBS is ok, I use (and prefer) a Stoney Point (now Hornady), and Wilson makes guages where you simply drop the case into the guage to see if it will chamber and if the cartridge headspace is within min and max specs.
I have a scale, butwhat other tools would you recommend to create accurate reloads?
A dial caliper. Just buy a chinese made version for around $20. All of the RCBS, Lyman, Hornady, Cabela's, etc calipers are made in china and simply carry different brand logos on them. You can buy a set from Harbor Freight for the lowest price. The next level of quality and precision in dial calipers starts at $100+. Avoid plastic calipers- they're junk.
Rubber O-rings: Buy a 1/2 dozen of them that fit around the ram in the slot that holds the shell holder in place. Remove the shellholder retention spring, throw it away, and use an O-ring to hold the shellholder in place. The brass will feed into your sizing and seating dies with less interference and you should get straighter ammo.
Imperial Sizing Die Wax- Skip all of the other case lubes and move on up the learning curve- this stuff is the best. Might not make any accuracy difference, but will make reloading much easier and less messy. It also lasts a long time and you'll never have to 'invest' in a stuck case remover *cough* Hornady one-shot*cough*