Tom - permanently compressing the wad is entirely possible when you crimped it. I prefer built up wad columns with card and fiber wads, only using the gas checks for holding the ball centred and as a gas check. The built up column still has a bit of 'give', but is also firm and deliberate in it's exit from the muzzle. I believe compressible wad columns can compress crooked (Ed's pictures show this) and send the ball or bullet off at an angle to the muzzle as the wad opens unevenly in relation to the line of departure.

I'm confused again - are you using a 10 bore or a 12 bore?
The .690" should work in a 12 bore just fine, as it is a 14 bore ball - of about 495gr. in pure lead.

437.5gr. to the ounce. A .715" ball usually weighs 1 1/4 ounces at 545/6gr.

If a 10 bore, I'd think a .740" ball would be about as undersized to the .775" (10) bore as you'd want. A .740" ball in pure lead will only run 600gr. A true 10 bore .775" ball is 700gr. according to my chart, just under the 1 5/8ounce load of shot for weight.