Call Ray Romain at (814) 265-1948. He built mine, its a heck of a shooter. He was a pure pleasure to do buissiness with.
You gain probably 50 MAYBE 100fps over the regular RUM, its up to you if its worth it. Loaded 300RUM ammo can be shot from the tomahawk chamber, so that maybe a plus.
This is an AVERAGE group just over 2 inches shot at 450yds in 7-9mph winds. Ben called the last shot left.