All over the place - Primary Arms SLx 4-14x44mm Rifle Scopes, 30mm Tube, First Focal Plane (FFP)

I got this scope, put it on a tack driver 308 and can’t get it to group. I swapped scopes with a different rifle and ended up having the same problem on the other rifle. I sent the scope back to primary arms were they “fixed it” and sent it back. It is worse than before sending it to them. I called them back and they said I probably didn’t have it mounted right. I checked it all again took it out and had the same issues. I can’t get a 6 inch group at 100 yards with the scope on a rifle that I get a half inch group with a cheap Vortex.