"...is going to have roughly..." That from some computer program? Speer, like every other manufacturer, shows 147 grain jacketed ballistics for up to 100 yards, only. A 147 starting at 986 fps with 317 ft-lbs. at the muzzle has 887 fps with 257 ft/lbs. at 100. Won't have 755fps and 186ft-lbs left at 400.
Computer programs are mostly created by people who know nothing about firearms. And there are far too many variables for any program to actually mean anything.
Denim is not in any way bullet resistant, never mind proof, at any distance.