Hello,
I will make a pair of inserts to use a very pitted 12 ga barrels from an old Darne shotgun.
The idea is to make a 12 to 20 ga tube about 1 foot long, to avoid the heavy pitted area in the barrels.
My question is, the steel that it is locally available are:

-1518 carbon steel or
-T-304 stainless steel.

Could you tell me what material is better for the purpose?

I will work the material in a lathe.

Thank you for your replies.

Best,

Jose

Jose M. Fernandez