Anti-cant devices: I am in favour of them, I think they're a nice optional-extra for target shooting on surveyed, level, uniform rifle ranges, and I think they're essentially required for long range (more than 600y) field shooting.
Anti-cant devices: it is important that they are installed well-aligned to the scope's reticle.
Anti-cant devices: an interesting note is that it doesn't matter whether or not your scope is carefully plumbed w.r.t. the rifle action or not.
And now on to the rest of my increasingly-drifting reply....(!)
I think we're approaching this from different angles. You're coming at it as a target shooter where it's mostly about group sizes and I'm thinking long range hunting, one-shot-kill kinda thing.
You're interested in precision, I'm thinking accuracy.
Depends on the kind of target shooting, but most target shooting is about accuracy (i.e. we are judged on the basis of how far each of our shots land relative to a predetermined point). It's only in shooting-for-group (some but *NOT* all BR) is the actual position of the group relatively unimportant.
Accuracy starts with precision. Accuracy is precision, *plus* locating your precise shots at a desired place. One can have high precision with low accuracy (e.g. I put ten shots into 10" at 1000 yards, but they are 40" away from the centre of the target). But I am not aware of a scenario in which one can have high accuracy but low precision.
"long range hunting, one-shot-kill kinda thing" is a lot like long range target shooting - only more difficult. All of the lessons and knowledge from long range target shooting apply, plus of course there's a lot more you have to master which you'll not get from target shooting.
To do well in long range target shooting, it is important to understand the capabilities of the gear you are using (for example, its grouping ability at different ranges, the amount of wind drift, etc). It is also important to know the mechanics of shooting, at what does/does-not matter in setting up a shot, and the nature of that (for example - it is useful to know and to understand that at long range, canting can give you meaningful windage errors. It is also useful to know that at short range there is very little windage error due to canting, in many cases and for many applications it can be treated as nil).
29" is a lot when your target is a 20" kill zone. At the end off the day, to let an error put your PoA (Point of Aim) off even half of your rifle's group size isn't acceptable. What's the point of investing all this time and energy into precision shooting if you're going to let something silly like not having a bubble level put you off even the slightest? It still surprises me to see so many long range rifles without a bubble level.
And don't get me started on angle cosine indicators! (I guess those are more for field shooting but still...)
Agreed - long range rifles for field shooting should have a bubble level, properly installed, and properly used. Shooters should understand the simple takeaway about rifle cant - DON'T CANT.
I still maintain that thinking about target sizes, windage errors, rifle grouping ability etc in MOA terms is an extremely useful level of abstraction.
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