[Drakker]

Only the Maple Leaf and the A+ will need a barrel with a larger window or an open cut. The A+ should fit fine in a barrel with a larger window like the PDI above, the maple leaf will most likely need an open cut barrel, but it should be possible to enlarge the hop-up window on a stock/upgrade barrel enough to fit the maple leaf. You can also turn any barrel into an open window barrel by remove the unneeded part. It's not a hard job, but you must make sure no not remove extra material and keep the sides of the window as "equal" as possible.

An A+ rubber will actually fit in the stock barrel, but in mine it got damaged after a few games by the somewhat sharp edges on the hop-up window. It really needs some extra space to be durable.