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If you don't like the idea of trusting a brush on a cleaning rod, there are alternate methods. The most accurate and complex, it to make a casting. Another way, is to use a simple wooden dowel that loosely fits your bore. You'll need a good light for this to work. On the tip of the dowel make a contrasting radial mark. Inset the dowel from the breech until it passes the chamber tooling and align the tip where the rifling starts. Holding that position, make a mark on the dowel at the muzzle intersection. Now, carefully observing the rifling and the tip of the dowel while drawing the dowel down the barrel. You'll be twisting the dowel so as to keep the radial reference always aligned with the same groove. When the radial mark does one complete revolution, stop! Now, see how much additional dowel is protruding from the muzzle measured in inches. This is your twist rate. To check, keep pulling and twisting to do complete a second revolution and stop. Now the amount of protruding dowel should have doubled. For each additional revolution of the reverence mark the protrusion should increase proportionally.
A point to remember: This and other methods are for uniformly cut rifling -- the twist remins constant for the full length of the barrel. Barrels have been cut with what's known as gain twist -- it gets tighter the closer you get to the muzzle.
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