I've got the model 7 in 6mm. Mine's 23 years old and i've never shot anything but 100 grain corelockts thru it. It's always shot well. I'm actually surprised that after your initial terrible groups that you actually got it tuned up as well as you did as I would not generally expect the gun to be that finicky, so if it was, I would have said "dud" as well. I'm glad to hear it worked out for you. The only gun that I've had that shot terrible groups never did shoot well with anything (brand withheld)

BTW, is your's an older model? or the cdl? or the ss?