The older ones you will only get a factory lug in. The newer ones have been opened up, A .250 lug just fits although I still recomend opening it up abit bigger.
i got a new SA 2.0 from Baur Arms in March and the lug slot was .186" IIRC. i had to chuck the barreled action in a lathe and face the front (muzzle side) of the recoil lug to .184". i don't know whose recoil lug was on the barreled action, but this worked fine.
My 5R fit fine with plenty of room. The barrel looks like a frickin toothpick in the barrel channel.
If things work out like I am planning I will have a custom build to put in the aics withe a heavier barrel.