I've had better luck with the Win SUper X 180's than the Federal 180's. They are the only 2 I have fired. I have a 35 year old Parker Hale with only about 60 - 70 rounds total through it, most of the use seen in the last 2 - 3 years just to sight it in. I used to use the Win Super X 180's until last year when I switched to the Federal 180's Power Shok.
With the Win's, I had no trouble getting on paper and staying relatively tight - about 1.5 - 2" groups @ 100 yards with a brand new Tasco Golden Antler 3-9x40 scope (I know, its a cheapie but it does the trick). With the Federals, I can't get better than a 6 - 7" group (incedentally, the same day I shot several 0.75 - 1" groups with my Win M70 in 30-06 firing Federal 165's Vital Shok - I posted them a few weeks ago).
So I recently took the 303 to the local gunsmith for a quick check - the scope and mounts were fine, headspace is absolutely not an issue, a few other items which I can't specifically remember were also checked out and they were fine. The only thing he found was heavy fouling towards the end of the barrel - a lot more than we expected considering the limited use the rifle has seen.
So after a good cleaning, I'm waiting for the next opportunity to go to the range. I'll update when I can.
I should also mention that I'm just getting back into shooting and hunting after being away from the activity for many years due to work committments. When you fellas get discussing the benefits of handloading, headspace issues, fire-forming, etc., its all a little over my head but I'm coming along slowly.