Steven,
If they had the chambering reamer resharpened, making it right on the edge of being too small in the neck. This would answer why it would work with one brand of ammo and not another, with maybe thicker necks. In my experience, 5 groove barrels are much more common than 3 groove. I suppose if the grooves are cut, one at a time, three would be quicker, therefore cheaper.
Mike

Last edited by Der Ami; 12/24/16 02:48 PM.