I use both Grim Reapers and Thunder Heads 125 grain.. I can't tell which kill better, they both do a good job.... Of course this defeats the purpose, but I open the Mec. when I nock an arrow... Just to make sure they don't fail.... ( I know, I know, why use them at all?) Because I have three, and I am going to use them until they are histroy......I paid 35.00 for them, and I'm going to get my money out of them.. Then I will go strictly with a Muzzy...