we did a bit of testing on the Maxx 55 and found that they will shoot @265-280 fps with a heavy spring. Ball detents were an issue also.
we ended up machining the body and installed Tippmann detents but with the huge bore, they had issues with accuracy, so we made some .50 barrels.
they shoot ok, but we did see some ball breakage at the breach due to it being larger than the barrel bore. overall, not a cost effective modification for field operations.