a 9 groove barrel?

[CoyoteJoe]

I couldn't really decide where to put this question but here it is.
I received a T/C barrel from a fellow who wanted more traditional sights on it. The barrel carries the normal T/C markings of .45 caliber. However it is actually a .50 caliber bore rifled with 9 grooves. Yes, nine, I counted them three times because I couldn't believe it. I couldn't measure the exact groove depth but clearly deeper than a typical T/C and not so deep as Green Mountain so I'm guessing .008-.010". The twist is about 56" as near as I can measure.
Clearly this is a re-bore but I'm wondering "who cuts a nine groove barrel"?

 

[LRB]

If it is marked 45 cal., but is a fifty, it was likely rebored. If it is a TC marked 50 cal, it is one of their early first run barrels. They were, in general, very inaccurate because of the rifling.

 

[CoyoteJoe]

I have no doubt it is a rebore but the question remains, "who cuts a nine groove barrel"?