They vary, sometines a lot. I've had 3 of the exact same Knight rifles from the same run, and all had different bore diameters. .501", .5015", and .502".
Cerrosafe is one way, check Brownells for information on that.
With an unloaded rifle, and breech plug removed. Safety first!
There is also another way you can slug the bore to know for sure. If you have a .54 (.530"ish) caliber pure lead round ball, take a dowel and brass hammer and knock it in the bore an inch or two. It will shave a lead ring off, sorta like loading a cap and ball revolver. Then from the other end knock it back out with a long dowel or brass rod.
If you don't have an oversized round ball, take a pure lead conical and stand it upright on a CLEAN hard surface. Then take a CLEAN hammer and give it a good whack. Measure the O.D. until it is around 0.005" over nominal bore if you just want the land diameter, or at least 0.010"-0.015" if you also want the groove diameter. You can cut this slug down with a CLEAN (new) hacksaw blade before or after giving it a whack or two to belly it out. It sometimes helps to use the nose of the bullet and 3/8"ish of the bearing surface. That way you can get the ogive beyond the crown to help keep things centered while you lightly pound it in with the brass hammer and wood dowel. If you have the false muzzle, it probably isn't going to make a difference.
I can't stress enough to keep everything clean, so you are only using pure lead, and not introducing other small abrasive metal particles in the lead that can scratch your bore.
After pounding the slug back out so it lands on a soft object, the land (muzzleloading bore) diameter can be determined by measuring the now grooves in the slug if you have an even number of lands and grooves. The groove diameter can be determined by measuring across the largest diameter of the slug. This is easy with 6 or 8 land and groove barrel because the lands and grooves are 180º from each other, but with a 7 land and groove barrel, not so much. They take a few more measurements and some math to figure out!
Just be safe, and let us know what you get. Some of the Traditions have extremely deep rifling, so let us know what you find out. My Whites have about 0.0035" deep rifling (.504"/.511", .451"/.458"), my Knights and H&R/NEF Green Mountain barrels about 0.004" - 0.0045" deep rifling .501"/.510", .502"/.510", .502"/.511", .451"/.459"). This is a perfect rifling depth range for full bore conicals and saboted bullets, IMO.
