I cant the rifle on purpose it just depends.
Most of my rifles are very slightly canted to level the scope to gravity because in my shoulder pocket the rifle is ever so slightly canted.
On other occasions like shooting positional, (targets are usually not super far) I cant the rifle again.
The Tubb Rifles are designed to cant the rifle, and level everything necessary after the fact. There are more than one locations for the scope base, they are at 5 degrees or 10 degrees besides being top dead center. So you have 0 degrees, 5 degrees, and 10 degrees of cant built in.
Watch his video and he speaks about "your shooting style" quite a bit. What he means is adjusting the rifle to your natural cant. Then you can level the rifle after you set it up.
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In part 2, he talks about the receiver holes.
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So, canting is not a "cut & dry" issue... if you cant and don't account for it, because you are "level - level" you run into long range issues. If you purposely cant and account for it, there is no issue at all.
People naturally cant the rifle, so going level - level and not accounting for position, comfort, fatique, etc, you will naturally move the rifle off center. If you set up for the long term, and set up the rifle to your natural position. You won't subconsciously cant the rifle causing an issue.
But you can "cant" a rifle, and have no ill effects. Or in most cases, much less deviation than reported. Granted the farther out the worse it will get, but most cant very little and will probably see the effects of a bad trigger press before they see the problem with canting.