When buying arrows, buy the best you can afford. If your gonna skimp on your setup dont let it be on arrows. As far as arrow weight, id suggest something heavy since you only pulling 50lbs. If i was shooting 50lbs id want my arrow to weight at least 430 grains(or there about,and probably higher). It may be overkill but thats how id have it. As far as the 55/75, it means that arrow is for draw weights between 55lbs and 75lbs.