Steve of RRA (RRAModerator in the Industry, RRA section) has a tacked thread where he provides the codes. As he works for RRA, I'm guessing its accurate.
Applicable "codes" for 223 barrels:
Old Codes:
Three characters side by side over the chamber.
First Character: N or W...N for NATO chamber or W for Wylde
Second Character: 8 or 9...8 for 1:8 twist and 9 for 1:9 twist.
Third Character: A, S, or C...A for moly (chrome -moly Alloy), S for Stainless, and C for Chrome-lined alloy.
New Codes:
The actual base part number from our parts system/catalog, located over the chamber. These are the most common. Unless indicated otherwise, all stainless barrels are 1:8 twist and all moly barrels (chrome-lined or not)are 1:9. All 16" moly barrels have a NATO chamber, while the 20" moly and all stainless barrels have a Wylde chamber.
200 Moly CAR
200CL Chrome-lined CAR
202 Moly R4
204 Chrome-lined R4
205 Chrome-lined light-weight R4, 1:7
206 Stainless CAR
208 16" varmint
209 Moly 7"
210 Moly Mid
212 Chrome-lined Mid
213 Moly light-weight Mid
213CL Chrome-lined light-weight Mid
215 Stainless Mid
218 18" varmint
219 Chrome-lined light-weight R4, 1:9
220 Moly Std (rifle)
221 Chrome-lined Std (rifle)
222 Stainless NM(rifle)
223 Stainless NM (rifle), unthreaded
225 Moly 10.5"
225CL Chrome-lined 10.5"
226 20" varmint
228 24" varmint (1:8)
229 24" varmint (1:12)
232 Moly light-weight CAR
232CL Chrome-lined light-weight CAR
YOU MAY START TO SEE SOME "S" AND "C" MARKINGS AFTER THE NUMBERS...THE "S" FOR STAINLESS AND THE "C" FOR CHROME-LINED...PRIMARILY TO HELP PEOPLE BOTH IN-HOUSE AND OUT TO KNOW AT A GLANCE WITHOUT HAVING TO REFER TO A CATALOG.
Steve/RRA
Edited 07-07-06 to include chrome-lined 20" rifle bbl (AR0221).
Edited 01-04-07 to include chrome-lined lightweight R4 bbls (AR0205 and AR0219).
Edited 01-30-08 toinclude the 7"(209), 10.5" (225), and light-weight CARs and Mids (232 and 213)
You may want to go over to that thread and ask him directly.
LINK