Yes many vintage guns will take modern pellets. But there are examples in my collection that I like to shoot that require something special. Manufactures tend to eliminate items that don't sell very much. One example today H&N made round balls that were 4.54 mm. Perfect for my Haenel 28-R where the bore lets 4.5 roll right out. Went to buy more they were eliminated from my normal mail order site. Found just one 500 tin at another site and ordered it. Went on H&N site and don't see them made any more? Another gun that is difficult is the Crosman 102 another with feeding issue. Buying vintage pellets has been helpful at times, where they aren't too expensive.