As a lefty, I have left several 8 - 10's in the last month, it's the same as a righty 7 - 9. In my case, they all appeared to be slightly high entering the pocket, with the ball driving straight through the 5 pin, and missing the 8 pin. I throw 15 lb. at about 15 - 15.5 mph, BTW.
Up until about a month ago, I couldn't recall leaving that more than once or twice a season. In the last month I have left 1 or 2 of them every session. I don't understand why I am suddenly leaving these, but it could be possible that I am getting a few more revs on the ball off my hand.
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"Beer is proof that God loves us and wants us to be happy." Ben Franklin
Enjoy,
Bob