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If I remember correctly you want to have 55lbs KE minimum to shoot mechanical heads effectively. Even then you should stick with the smaller cutting diameters of 1 1/8" for example.
I may be off on my figure there so anyone feel free to chime in.
Shooting bigger heads like 1 1/2" or 2" cutting diameters requires even more. If you are marginal then just play it safe and shoot a fixed head. There has to be one out there that will fly right for you. I myself bought 3 sets of heads this year. Magnus 100 grain Stingers 2 blade.......SteelForce 100 grain 4 blade serated.....and Muzzy 100 grain 3 blade(These were sent to me free by Muzzy because I had trouble with the 90 grain 4 bladers last year)
I myself believe if you are under 60 lbs KE you are asking for trouble with penetration of a mechanical head.......I was in the mid 50' s last year and the buck I shot with a WASP JAK-HAMMER.....the head stopped at the opposite side hide. Between the ribs through the lungs and right through the middle of the heart (see pic below
).........I would hate to think what would have happened if I clipped a rib. With no exit hole I was left with a VERY difficult blood trail and it took me and 3 hunting buddies an hour to find a deer that was dead 10 seconds after I shot him.......scarey.
I don' t know about you guys but after last year I want to see BLOOD!!! I' m talking blood that flows.......not drips. Now I realize that you have to make a good shot to see that kind of blood but I feel like I made that shot last year and didn' t get the red brick road I was looking for.
The WASP JAK-HAMMER did what I wanted it to do. It flew straight and killed the deer I shot at very quickly. Great head and I recommend it highly to anybody with enough power to get a passthrough with it.
I myself have placed priority #1 on penetration this year.........straight flight is a must......but that is true of ANY head. My goal is a passthrough if I make a good shot. It is hard enough getting a deer inside 20 yards of your stand and then making the right moves and perfect shot placement.......the last thing I ever want to do again is feel the fear I felt when I thought I might not be able to find the buck I KNEW I had killed.
I DID my research and picked as small a head as I could find and made a perfect shot and I still almost lost that deer due to a lack of blood to follow. I wish mechanical heads were REQUIRED to list KE minimums on the packages.
They make some really great heads today but I can' t even count how many times I have heard someone say a mechanical didn' t work for them and 99.9% of the time it is because their setup was not powerful enough to utilize that head.
Of course it doesn' t help that they fly so well because that is lure enough to get people to buy them. Combined with some pro shops and sporting goods stores that will sell them to anyone and in fact recommend them to people because they fly so well causes many failures IMO.