Originally Posted by fishngrits
RRA doesn't put caliber markings on their barrels. 212CM indicates it's a chromed-lined midlength barrel, IIRC. It is a 5.56mm chamber. Most RRA barrels/chambers are 5.56mm, the rest are .223 Wylde. I believe all of their carbines are 5.56mm. The is a RRA barrel code thread in the RRA Industry section on AR15.com.
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Here is the bbl code list from AR15.COM:
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.
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:
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.
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)
Here is a direct link to the thread:
AR15.COM :: Forums :: RRA barrel code list.