These bushnell banner scopes are junk. I have had one for about 4 months and it has recently tore up. It is a 6-24x40 and it started not focusing about a week ago but today the power ring started locking up not being able to adjust it. Just my luck the 90 day refund warranty has just expired. So now I get it all in mid-way money.

Try one of these next time... http://schmidtbender.com/

It seems the Banner has a thin tube. I have seen this happen to a couple of others. If you slightly bend the tube through poor mounting or even slightly too much ring torque they are easier than they should be to kink or bend the tube. The two I have seen that had this problem eventually suffered a frozen power ring like you describe. One was mounted in some of those Millet Mangle-Loc rings. The owner had put too much pressure on the tube by moving the rear windage mount too much. The other never knew for sure, just suspected his cheap rings. But sure enough when it went back to Bushnell they said the tube was bent. I think them too flimsy though if you mount them carefully with low torque they seem to work pretty well at least on low recoil rifles.

you can move the power ring freely from 6 to 8 but no farther. I had it mounted on a 270wsm.

I have one Banner, a 6X20, and it doesn't hold center. My Trophies are fine.

i find banners are good 22 scopes, just not fit for centerfires