There is a ton of misinformation out there about the difference between the 223 and 5.56. The biggest difference is the chamber dimensions between the two, 5.56 ammunition is typically loaded hotter than 223, and the recommendation is that it should not be shot in rifles with 223 chambers.
There isn't necessarily a big difference between 5.56 and 223 brass. All brass has variations, and even more so from different manufacturers. You can use 223 or 5.56 headstamped brass to make either type of ammunition, and is why the reloading dies are the same.
Reloading data from a book or online has a lot of variables. They state the primer, brass, and bullets that are being used, and then give a safe range of charges for a certain powder. Things like temperature, chamber dimensions, etc are unknown. This is why you should start at the lower end of the reccomendation and work your way up to find out if your combination will work with your rifles.
If you want to keep costs down, the 55 grain FMJ and SP bullets are good but not the best for precision.
The 52/3 grain Sierra and Nosler BTHP offer good accuracy, and excel at 100- 300 yard shooting.
For varmints, the 53 grain Vmax is a good choice, especially with slow twist barrels.
The heavier class bullets with a higher BC, such as the 69 and 77 grain, work great for longer distances.
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