41--witness mark on left side of barrel?

[7cstevan]

Brought my recently acquired 41 (made 1958) to the range tonight--practicing with iron sights and got to chatting with another guy who uses his as his preferred bullseye gun. He bought his new in the mid 1980's. He pointed out that both our guns have a small vertical line in the barrel, about 1" back from the muzzle on the left side only. He thought it was a flaw or tooling mark in his and was surprised that my gun made 30 years earlier also had it.
Anyone know what it is for? Perhaps a witness mark to line up the (optional?) external barrel weights?

 

[TOM BECKWITH]

Index mark for 3 piece under bbl weight set.

 

[7cstevan]

Thanks Tom, a great help once again!

 

[BruceB]

Yup, what Tom said.

 

[civil1977]

And here are some pictures to better illustrate this:

 

[7cstevan]

That's the mark, exactly right
Thanks
Steve

 

[Troystat]

Thanks for the info, I was wondering what that mark was for, I just had not gotten around to asking about it.

thanks

 

[Vectorxw8]

I have heard from others to be thankful the former owner did not have the weight set as they scratched the barrels something awful. Scott