Hi, I`m into making a few muzzle loading barrels and sorting out the best steel. I think the ones made in Spain are made of 12L14 steel as this is easy to machine and strong enough for black powder. Just up from that steel is 12/15 grade steel and this is what I was thinking of using. It`s still good to machine and a lot better to what they had in the 1800`s. Now the grades are what I can get in New Zealand and could be different in the US, I know Green mountain use 1137 grade for their M/L barrels, not sure what that would be over here. So am I on the right track. Thanks, Homebrew.357 .