No matter the shape of the action, the rotational intertia that the bullet transfers to the action is pretty minimal. What keeps a round action from rotating is it's contact with the stock and the action screws holding it in place. Jim Borden did some engineering studies on this and published the results as did Dan Lilja and the late T.J. Jackson.
As a side note, the action screws 'see' virtually no side loading from firing. Their single purpose is to provide adequate clamping force between the action and stock. The common 1/4" action screws are actually very excessive for the job they need to do. The round Hall actions (and a couple others) that are designed as glue-ins have 10-32 screws instead of 1/4-28's, for example. I've converted several of those to bolt-ins using the 10-32's and lots of side clearance on the lugs with no issues. If you look at the load tables, an 8-32 would still be more than adequate for the job.
The next time you get a chance, take a barrelled action and hold it at the barrel shank and fire a round. You'll be amazed by how little 'torque' there is.
Good shootin'
-Al
