Have a 12/223 valmet barrel that I want to rechamber to 3". Can I just rent a 3" reamer and dyi? I do not know if the barrel is chrome lined---is this a problem if it is? I know its no prob with the action, as my 12/3006 barrel is a 3" chamber. Any advice appreciated.

if the barrel has the needed wall thickness then you can use a reamer to lengthen the chamber. if it is chrome lined then you will ruin a tool steel reamer. to test- just dab a patch with cold blue on it in the bore. if it doesn't blue- it is chromed

As Max said as long as it isn't Chrome lined. You can rent a reamer.
http://4-dproducts.com/display...wid=289&tname=rental

If it is lined enjoy your 2.75"