I bought a magnetic collimator and I think it was well worth it!

I had one end of the barrel that wasn't exactly square (90 degree from bore). It was off by at least 1 degree (a little more than 60" at 100 yards.)

But that was very odd, I thought.

In general (all but that one rifle) it has worked very well. Now, the first thing I do when I mount a scope is check it out with the collimator.

Thanks to MD for another great recommendation.

I prefer classic.
Semper Fi
I used to run with the hare. Now I'm envious of the tortoise and I do my own stunts but rarely intentionally