I started with Muzzy three baldes, went to 4 blades and am back to three blades, all 100 grains. Here is my reasons. The first year I hit a deer and got clean pass through, I thougth it would be nice to try 4 blades. They just look "deadlier". So I switched. That year I hit a deer quartering tword me in the shoulder so the arrow was medial to the front leg at about a 45 degree angle from the mid line. The head penetrated the bone behind the shoulder joint just enough to puncture the left lung. Then I started to look at the difference in the heads. The heads weight the same, 100 grains, but there are 4 blades as opposed to three. So how do they make up for the weight of the 4th blade? They make them shorter and increase the angle from tip to base so the 4 blade actually contacts more flesh which slows the arrow faster which results in less penetration. The blades on the three are longer and not as great an angle tip to base. I can't remember the cutting diameter of either the 4 or the 3, but I think the 3 is less than the 4. Again, Im not sure but I think the 4 creates more drag as it goes through tissue and bleeds off KE quicker than 3 blades. For lack of better terms, they just look "blunter" than the three.
Don't know if this makes any scence, and I'll stand corrected if I'm wrong.
The 'Bonker