hay friends,my son is 16 and has built a ar15.mostly with ebay parts.he don't want no money help from dad,so he built gun on a spikes lower and a Anderson upper,ebay barrel and it shoots like crap.its shooting 4 inch group at 75 yards,with match grade ammo, can anyone suggest a good barrel that maybe he can afford or give some sug. on how to get gun to shoot better? thanks