The old bolt looks fine, hell the carrier looks fine too. I hate to think it's done for, it's a Colt and wasnt cheap. I got it used and burned at least 5k through it myself. I dont suppose I can measure it without more tools that I have. Is there any part that may have become clogged up that needs cleaning out other than the hole through the carrier key to the bolt? Should I pull the gas key and look for anything under there??