You don't need any special rifle, just lots of training using what you got. Also you don't need to be a big bodybuilder, you need instead lots of physical and mental endurance. Look at Taliban, they're all skinny, but fit (not skinnyfat). Parkour, obstacle courses and stuff you have to crawl through/under is good training, especially if you incorporate target shooting while your heart rate is high and you're exhausted. Also get a bayonet, that's more useful than MMA 1-on-1 sports fighting.
But if you're targeting is niggers, then you're just wasting your time. The correct target is the puppetmasters. In the end, your best asset is going to be your brain.