[doneroman]

Well, doing my first build and ordering parts from several vendors. Barrel vendor won't be ready with stock for 2 months or so, so I don't have to pick the barrel yet. Going with the RRA upper/lower combo.. Anyway,...

a.) I'd prefer the 18" or 20" barrels, vendor I like has 1:9 twist. What is the best weight 5.56 bullet to use for this configuration that's good for match, mil., and L.E. use? Am I looking to cover too many bases with 1 upper?

b.) I see folks saying there is a difference between 5.56 NATO, .223, and .223 Wylde. What's the differences? (These barrels I'm looking at now are 5.56 NATO, according to the manufacturer.)

Thanks for your educated insight.

[Constructor]

A 9 twist will handle up to 69gr bullets, some 75s but that may be pushing it.
The 556 and Wylde have longer throats and will handle full power M193 or M855 loadings. A 223 chamber throat may be too short and cause excess pressure.