I'm looking for advice on which ammo to try in my AR. It has a 16" 1:7 chrome lined barrel. The previous owner put 60rds through it and told me it likes 62grain ammo, but with only 60rds downrange...... I know the 1:7 is for heavier loads, but what is considered heavy, 62gr 69gr?? I'll be shooting from 50-100yards. 100yards is the max range where I shoot until I go out to the woods. Another question. Where do you buy bulk ammo online?