I'm shooting my bow 70lbs at 30" draw with 125 grain muzzy 3-blades. If I was to switch to a 100 grain mechanical, how much difference should it make in my groups? Are we talking a foot or an inch at 30 yards? I'm really not satisfied with my muzzy 3-blade broadheads because I can't group them consistently from farther than 20 yards. I'm good with field points all the way out to 30 yards, within a 2" to 3" group pretty consistently.

First off what for arrows are you shooting and has your bow been properly tuned? Because if your bow has not been tuned the Mech.'s will only mask the problem, and the mech.'s will not penetrate as well out of a poorly tuned bow. I am no expert but these are some likely problems.

I agree with the above post. go to www.broadheadtests.com and click on the tuning page. I explain the basics of broadhead flight as well as provide some basic tuning info. I also have links to some of the better tuning guides.

Spine is critical with fixed blade broadheads. In addition, if spine is correct, heavier heads fly with more forgiveness. In order to give an opinion of your setup, we'd have to know the specifics of the bow and the arrows.

Also, if your groups are good at 20 yards, they should be proportionately good at further distances (unless it's windy).