Well i just finished building my lower from the group buy we just had and ive finally decided on a 7.62x39 upper i was wondering if i could use a stripped 556/223 upper receiver or do the make specific ones for 7.62? Ive tried searching and i find 7.62 barrels and bolts so would it be ok to use a 7.62 bolt and barrel on a 556/223 upper?