I initially considered the slower twists as recommended by Forsyth - but in deference to the increased powder charges normally needed to gain accuracy with them, I suggested faster twist rate. My 14 rifle shoots as well with 140gr. through to 200gr. Even 140gr. with a 700gr. 10 bore ball is going to get your attention. It is doubtful you will get good accuracy with light charges, even in the faster twist. I would think 120gr. to be a minimum charge.

This 'light' load shoots well in my buddy's 11 bore rifle, but for shooting past 50 yards, as in 100yard target or for hunting, he uses 150gr.2F. That is in a Don Getz 66" twist barrel. he initially started with 200gr. 2F as that shot well - it also kicked well in the 9 pound rifle, so he reduced to 150gr. for hunting moose. That rifle & load simply staggers them.

If a person was going after buffalo, elephant or tigers, then perhaps the slower twist would be OK due to the greater powder chargers.