If your gym has a pullover machine, give it a try. If nothing else it is a good finisher at the end of a pectoral workout.
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I use the Hammer Strength pullover machine. There is zero pectoral involvement, zero. With dumbells I can see why people might think it's pecs as you hold the dumbell over your chest, very minor stabilizing by pecs. Some also do the lowering to the chest thing
But on the machine it's all back.
I did the dumbell pullovers starting out, 30 reps with the heaviest dumbell, which was 100lbs at my gym, lying cross bench at the end of some back sessions. I really lowered my hips. I think I got a umbilical hernia from it and I knew it was a tricep tear waiting to happen