Hi OutBack,
Not all .223 loads will work in the AR rifle. Many loading manuals are not very good at making this clear. The new Sierra Manual (Fifth Edition, I think) separates out .223 Bolt Action data from AR data. Sierra also has a very informative chapter detailing reloading techniques for the "Service Rifle", including some recommendations regarding powder selection ( Varget, Vihta Vuori N135 & N140, and Reloader 15 being top choices). Hornady's fifth Edition has a separate listing for the 5.56 Nato round, but it's only data for the heavier Hornady bullets. I don't remember seeing anything for 55 grain bullets. Speer makes a 62 grain BTFMJ w/cannelure which is supposed to be the duplicate of the M855 military bullet, but then combines the data with .223 general data. I strongly recommend buying a chronograph. I've got a Gamma Master Chrony which I got from Sinclair International. I've just started using it, but already I'm amazed at the information I'm gleaning. I already can't understand how people can reload for semiautomatic firearms without one.
Coolio