I have been wanting to build a 20 ga. bore rifle for some time. This rifle will be used mainly for deer and maybe a few pigs at shorter ranges, so no magnum shoulder breaking loads will be needed. I plan on loading in 20 ga shotshells and shooting a one ounce (437 grains +or-) slug over 70 grns (+ or -) of BLACK POWDER. I dont use smokeless and never will. If you were planning such a beast what would be your rifling specs? Twist and groove depth? And what slug design would you prefer with your suggested twist rate? Thanks, Ed