They are different rounds for different calibers (barely) w/different uses.
If you wanted a higher velocity 5.56 target round, then get the m193. Palmetto has about 3-4 different kinds for right around $6/box.
I dont think you'll notice that much of a difference between the 223 vs the 5.56 in shorter range target practice, but you can always get a few boxes of each and run your own tests. Thats the good thing about Palmetto State. You can mix-and-match up to 1000 rounds for the same $12 shipping.
I didn't realise you could mix them, that is a great thing. Thanks.