Let me just say that the 222 is an AMAZING little round and one I respect very much. I would much prefer it to a .223 or a 22-250 because of it's super accuracy and little appetite for powder. It also has a very long neck which also is very desirable to me. However, the 6 br has it beat in every arena except powder consumption and noise.
The most accurate cartridge and most "steerable" cartridge at 100 and 200 yards is not the 6br nor the 222. It is without doubt the 6 ppc. The 6 ppc is slightly shorter than the br and smaller in body diameter thus giving up a little more case capacity and velocity to the br. It is based off of the 220 russian case.
By all means, if you want the best 100 yard cartridge on the planet, go with the ppc.
If you will ever use the gun for varminting past 500 yards, and can settle for the 2nd most accurate 100 yard cartridge, go for the 6 br.
Using your 204 action will require you to open your bolt face to accept the bigger case head of the br, but a competent gunsmith can do this no problem.
The 6br remington was the first br and it has gone through several renovations since it's conception including changing the primer pocket size, and changing neck length. New 6br remington brass is now more like the 6br norma dimensions than it has ever been but it is still different enough that you must specify which kind of brass you will be using when ordering a reamer. THe Norma version came about as a change in the dimensions of the much superior Norma and Lapua brass from the Remington and because Norma saw the advantage of this case using a 105 grain VLD bullet to enhance long range shooting. By running an 8" twist in this caliber, you go from a 800 yard gun (with the 14" twist) to a 1400 yard gun.
Then there are all sorts of wildcats based off the 6br case like the 6 dasher and 6 br improved. These all have their place as well.
I own two br's. One with a 14" twist and one with an 8" twist that is improved. Both are deadly accurate, but in wind or really long range varminting, I much prefer to grab the faster twist because of it's superior bc bullets.
I would recommend any custom barrel that you can get your hands on, and DO have the dies made with the same reamer that makes your chamber at the same time.
The short action Remmy 700 for a 6br will work great. Just have it blueprinted and properly bedded and this cartridge will scare you with it's easy reloading, superb accuracy, fast clean up, and small appetite for powder.
One other thing I should add:
The Lapua 6br brass is probably slightly better than the Norma, however, check the reamer for neck dimensions because if you have to take more than .001" off the brass neck thickness on Lapua, you will be hating life. The Lapua brass is so **** tough that neck turning can become a nightmare. Norma brass turns much more easily and will last almost as long. If you order a reamer, make it for Lapua brass and make the neck dimension .271 or .270 tops. This would then only require you to just clean up the necks. My 6br improved has a .265" made for Lapua brass and it was a bloody mess getting it down that thin!
