Re: big guns means less accuracy
This is comparing apples and oranges.
If they are referring to big magnums as compared to the BEST 6PPC shooting at 100 and 200 yards, I would say no. The 6PPC will out shoot the big mags.
Now on the other hand, the Best 6PPC won't shoot at 1000 yards very well and the big mags will. Here is the REAL trade off.
Which one now has the BEST accuracy?
It depends on which type of shooting the person does and who is making this statement.
You can take the big mags, put weight to the stock and heavy barrels and they will shoot in the .2 and .3 range (and smaller) at 100 yards. Ask Steve Shelp about his 338 group.
If your talking about a light weight rifle and lots of recoil from a Magnum, the average shooter can't get good accuracy with it.
So, it depends on the yardage one is shooting, how much the rifle weighs, is it off hand, prone, benchrest and many other factors.
Point is, most BIG mags are designed for longer shots and better accuracy downrange.
The smaller cartridges are designed for closer shooting. Both have their place in the shooting society.