Have a chance to buy a used one, which I will eventually rebarrel. But, I will have to use it for awhile as a deer /varmit rifle. However I once read the rifleing twist was such that it wouldn't stabalize bullets above 90 grns.
what can you tell me about this, good loads and if factory ammo is still available. Any imput appreciated.

The original 244 Remington came with 1:12 twist which had trouble stabilizing bullets above 90 grains. When Remington changed the twist in their rifles to 1:9 they changed the name of the cartridge to 6MM Remington. If you're looking at a factory rifle marked 6MM then it's got the faster twist barrel and fine for just about any length 6mm bullet.

I always thought the story that the .244 with 1-12 twist wouldn't stabilize heavier bullets was a myth. That's until I actually got my hands on a nice old Remington 721 and tried some 100 grain handloads, which promptly keyholed their way through what targets they managed to hit. As Fjold says, if it is a Remington 700 marked "6mm Remington" (or even one of the scarce ones marked "6mm Remington Magnum"), then you should have no trouble with 100 grainers.