If you get a tight fitting patch, apply gun oil to it. Push that patch to the bottom of the bore. Now make a mark on the ramrod, and one on the end of the barrel. Now a 1-28 twist... the mark would make one complete revolution in a 28 inch barrel. So if you were to pull that ramrod up 14 inches it should make 1/2 a revolution. On a 1-48 the ramrod should make half a turn in the barrel on a 28 inch movement. A 1-66, 33 inches would make that mark turn half the way around the barrel.

The rifling will spin that tight fitting patch with the rifling as it moves up the barrel.. So if you measure the distance it has moved and how far it revolved around in the barrel it can give you some idea of the twist rate. The problem is, some people pull the patch through the rifling and this sets off the measurements.