Listed on the Cimarron site, are the 'factory standard' land and groove dimensions. One must recognize that a broach cutter does not always hold the exact numbers because a cutter being made of metal will wear making the cuts smaller. All barrel manufacturers will replace the cutter when normal wear exceeds the factory standards determined by a tolerance number.
This being said, slugging a bore is very easy ... a fishing sinker or round ball with soft lead is placed in the muzzle and then driven down the bore. Here's an Internet 'how to' video ...
I have been told to slug the barrel to find out the diameter but am not that trusting of my vernier caliper use.
If one is inexperienced, one might want to use their computer to determine how to do 'thing's instead of just posting up a question. In this example keying 'How to slug a rifle barrel' into their search engine will result in many explanations, such as ...
OK, Pedersoli standard specifications are: 450 lands and 457 grooves. My actual land - groove dimensions on two Pedersoli 45-70's are:
** 450 - 454
** 450 - 455
So, I just resize the 460 or 461 base diameter bullets to 457, reloaded and have fun. IMHO, the 'best' resizer is the Lee Lube Sizer because it pushes the bullet up through the die from the base of the bullet - not from the nose down as does the LYman H&I Lube Sizer ... which distorts the the axis of the bullet especially bullets cast from a soft alloy
http://www.factorysales.com/html/xcart/catalog/lubesize.html ... And if you need a custom diameter resizing die, they too can be ordered from Lee Precision - call them
Shooting BPCR one has to remember that that bullet base needs to be 0.001 to 0.003 larger than the groove diameter to properly obturate when shot. So as cast or resized bullets must be of the proper size otherwise poor accuracy will be obtained
OK Ellis, this is your morning lesson on how to slug a barrel and based on the results determine if bullets can be used as cast or need to be resized
Let us all know how you make out with the results of your morning lesson!