I switched from alum with vanes to carbon with feathers, i shoot 3 bld 100gr on the
alum thinking of going to a 75gr on the carbons for the speed. The 75gr is 1"
wide the 100gr is 1 3/16, will this make much of difference in killing effiency?
The heads are muzzys of coarse.

I used 75gr. broadheads last year, to me they are a little too light. I am going to 100 gr. heads this season!

There' s nothing wrong with 75gr heads. I' ve used them for years now with good results. And a deer shot through the lungs does not know whether the hole is 1" or 2" . Dead is dead. Two I would recommend are the Wasp SSt and the Innerloc, with a slight edge to the Innerloc due to it' s almost indestructible nature.
Actually, you might even find that yu get better arrow flight. Sometimes, depending on setup, carbon arrows get along better with the lighter heads.

25 grns in broadead weight is not going to gain you much speed so I wouldn' t switch just becuase of that. On the other hand, if the 75 grn heads tune and shoot better than the 100 grn heads, I would use them. 3/16" is just enough that it may make a differnce on a very close to marginal hit, but not enough to worry about in my opinion. Shoot the head that gives you the best accuracy and arrow flight.

I shoot 75 grain mechanicals with very good results. Good hits go a short distance and occassional less than good hits go a little further. I did put on 100 gr. practice points and found my that, at least to my naked eye, that my arrow flight was smoother so I' ll be trying them this year in the off season to see if I get the same groups. enjoy, Juniorpc

I find that a lighter broadhead will shoot flatter but you might not have the same penertation as the 100gns. I shoot 125gn broadhead and they work great. I think that if your shot placement is right you don' t need the extra 3/16" cutting diameter. So she' ll be right mate.