Ruger AC556 First Model in Excellent Condition. Almost all AC556 have a 191 serial number prefix. This early version has a 190 number. Note the wood handguard that was made for only a very short time. The sling swivels and selector are also different. Original blue is 99%. I have sold over 200 of these guns and this is only the third 190 gun I have had. Very scarce collectible.