New bow, new arrow question

[Stringpuller#1]

My first working set up is a Wes Wallace "the Mentor" it's 56lbs at 28". My arrows are Easton Axis Traditionals cut to 30" 340's with three 5" feathers and a 75gr insert. Adding the 165gr Simmons Landshark weighs it all at 585gr total. I haven't calculated FOC or put it on a chrono to get the momentum/ke numbers but it shoots flat and nicely, very stable and accurate.
   Now, that being said, it's a fairly long bow to shoot from my ground blind so I just bought a Ben Pearson Mach One 7052, it's 50lbs at 28", it's very light and short, says 52" on it. I figure it will be sweet for small game/turkey as well. When I put those above mentioned arrows through it they fishtail noticeably in flight, I even decreased the point weight to a 125gr field point with not great results either.
   I need arrows for the Ben Pearson, I can have them made I just need advice on spine and all that. I already have some Magnus Buzzcuts in 150gr on the way to me in the mail so I need to build an arrow to match that head to this bow.......help me please, thanks

[hawk22]

500 spine with a 50 grain brass insert and 150 grain point would work.  I'd start out with a full length arrow and cut down as you tune.