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While a Whitworth bore has flat sides ILO rifling, it doesn't include the extra (rifling ?) grooves where the flat sides meet.
Additionally, Whitworth's used a hexagon-shaped boolit - and not "normal" rounds balls/conicals.
In the mid 1800's, there was a LOT of experimenting in the US with various rifling types ( hexagonical, 5-groove, 6-groove, multiple grooves, etc, etc, etc);
AND there were hundreds of small, one-man shops that were building rifles - either making their own locks, stocks, & barrels ( including rifling) or buying the parts.
When they did repairs, they often used what came to hand, and fitted whatever to the best of their abilities.
Many never bothered to mark their builds, so there's no way AFAIK to positively ID your rifle.
Here are a small sample of the rifling styles tried back then (courtesy of Ned H. Roberts book - The Muzzleloading Cap Lock Rifle, pp.27)
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