Re: finding twist rate?
There's three ways.
Many reloading manuals have a table with the twist rate of various guns in it.
You could call the company and ask them.
Or, you could measure. Take a cleaning rod with a tight-fitting patch. Push it into the barrel a couple of inches. Mark the rod with a Sharpie (or something similar) at some type of index mark (the front sight works real good for that), horizontally at the muzzle. Draw a vertical line up the rod for maybe twenty inches (to be safe), in line with the index mark. Now, push the rod down the barrel. The tight patch will follow the rifling, the rod will turn. When the rod makes one complete circuit, which you will know because your vertical line is now at the index mark again, make another horizontal mark at the muzzle. Remove the rod and measure the distance between the two horizontal marks. The distance between the marks is one complete turn, so - one turn in 8 inches, or one turn in 15 inches, or whatever. There's your twist. I suggest you make your vertical line about 20 inches, because most smokeless cartridges have a twist faster than 1-in-20.
Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297
I always take precautions.
Beware the Evil Bullet Fairies.