What was the issue with the charging handle on the Chinese made ones?
9mm or a M16 clone complete with triangular handguards and prong FS.
I second this,
Include some retro Vietnam M16 look-a-likes.
I think the market is already over-saturated with flat-tops/M4's etc., People who want these most likely already have them.
There is a sector that wants a real budget entry level black rifle for a rock bottom price--how big it really is will be the tough thing to figure out.