What kind of 10 pins?
Flat or ringing? I'm referring to what the 6 pin does when the ball hits the pocket. If the 6 pin just falls into the gutter and lies there, That's a flat 10. When that happens, your ball may have "hooked out" or "Burned" up and is hitting with no energy. Shell down or increase your ball speed.
If it goes around the 10, (ringing 10) then your ball speed might be too high, causing your ball to come in behind the head pin slightly. Slow your ball speed, change your angle of attack or use a stronger cover.
Watch the 6 pin, it will tell you why you are leaving 10s.
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Nine in the pit with the Tenpin left standing. dooooh!!