4198 is a good, possibly the best choice for the .222. Surprisingly, 4895 does ok too (is there any rifle 4895 doesn't work in?
) I have also had reasonably good results with WW748.
I see no point to using magnum primers in the .222. There just isn't that much powder being burnt. Although, a specific combination with a mag primer might give good accuracy in your gun.
And that's the key. Which combination of what does best in your rifle.
.222s usually handle the regular 55gr flatbase bullet well enough, but the seem to live for the 50gr, or lighter. Despite their popularity these days (.223, primarily) FORGET heavy bullets for the .222. There is data for 60gr but my experience says they are, essentially, a waste of time, and money.
If you're lucky, your .222 will group the heavy slugs as well as a deer rifle, but not up to the standards of varmint shooting. If you aren't lucky, they won't even shoot that well.
The .222 ruled the benchrest circuit for many years, it is a very accurate round, and the rifles generally do it justice, if you stick with the bullets it is meant for.
Unclenick, are you sure your 600 is from the 80s? Maybe its a little older? I'm not certain, I'd have to check, but I'm thinking Remington dropped the 600 series in the latter 70s, although they kept building the rifles under the Mohawk name till the early 80s, I think.
I have one of the Rem 600s in .222. Really neat gun. I also have a 10" .222 barrel for my Contender. I'm a bit of an oddball, I'm not a big fan of the .223. I like the .222, and when I want more, I go to the .22-250. I skip the .223 for varmint shooting, no point to it, for me. I do have a .223, but its a Mini-14, and not a good varmint rifle.
Keep .222 loads to 50gr bullets or less, and load just short of max, and you usually see outstanding accuracy.