Several things to check but first off I have to ask are you using bags that are hard? Soft bags will move and the gun will move with them. Learned from Benchrest shooters use a good quality bag. (usually Leather) filled full. Protektor is what I use.
Grip yes it can do things, but also check the COAL ! This is important as with different lengths (bullet depth) things will change and keep a good crimp. Do you weigh each load? or use a charge? My Harrel Powder charge is accurate and I am reluctant to trust other brands on certain loads such as rifle cartridges. But my Redding seems to work good too. Check scale also. Eliminate the variables as best as possible and then it will be up to you as the shooter.
Practice does not make perfect,,, But Perfect practice does.

Edit to add,,, Try a different caliber and or gun, with the same setup. Look at the results and see if you are getting good accurate small groups or if you are all over the place. This might tell you if it is you,, or the setup,,,