Twist rate & bore size
 

What is the twist rate and bore size of a CVA Hawkens 54 cal.?

I will guess that the twist rate is 1 in 48".
The land to land bore size should be .54.
The groove to groove bore diameter would be slightly larger based on the depth of the rifling grooves.
The depth of one rifling groove should be doubled to obtain the groove to groove bore diameter.

There were some older CVA Hawkins that had slow twist barrels, but they are rare now. The new ones have a 1-48 twist. The bore diameter should be APPROXIMATELY .540 but there is no set standard. I would guess that a .530 ball and patch would work real well in that barrel.

This one is 26 yrs old. What is considered new?

If you want to get a rough estimate lay a piece of masking tape along the length of the ram rod and put a vertical line on it. Put your jag on and start a patch down the bore. Line up your line with a point on the octagon barrel and mark the rod at the muzzle. Push the rod down slowly allowing it to twist as it follows the rifling. When the line comes around (or half way around depending on barrel length) mark it again. Measure the distance between the marks and you got your rate of twist. Its not exact as it may skip but at least it will give you a rough idea.