[CHW2021]

The solution to not shooting well is to shoot more often.

Your rifles will handle the higher velocity, possibly avoid the cci minimags; but please do be aware that the cheaper "bulk" ammo does tend to be a little inconsistent in performance compared to the more expensive stuff. You will not get match performance out of it.
Please take your time shooting and ask the other guys at the range for advise, some issues will stand out to a more "seasoned" shooter; should you have a "death grip" on the forend of the rifle for example, expect to have your grip affect the shot placement.
I have been shooting over 40 yrs and still learn from those about me. Sometimes it is just what NOT to do.

Also, some rifles have a distinct preference for a certain ammo, buy a variety and see which performs better in what gun.

Above all, welcome and have fun!