I’ve always wanted that same thing, to be able to walk up to the bench and clamp the rifle in for a test of it’s consistency, not my skill. I remember a guy that sold airguns called Dirty Harry, and he clamped guns in a device to test for ultimate accuracy. It definitely showed you the guns capabilities, but only at about 20 yards. I think if you took a device like this Bog death grip, and attached the vice part to your bench securely you could use a tail bag and have a super steady rest. The Bog death grip was $199, it holds a heavy rifle very firmly although you’d definitely need to anchor the tail to get the repeatable accuracy you are interested in. Please post what you come up with and good luck with the project.