For me, turn hyper velocity into a gcd follow up of burst strike. Take it off continuation. Increase all continuation skills to 10range. Make double down either free or gives you two cartridges. Remove the third shell. Keep blood fest at two shells.

Or make bloodfest become double down after using it. I too have very few complaints about gunbreaker but moving bosses is more annoying than it needs to be and no mercy is a bit wonky atm.