Not really talking about a valid comparison here, as the long actions are by definition made for larger cartridges. There was a write up covering cartridge accuracy in Remington 40-Xs out of their Custom Shop that appeared in one of the NRA High Power books some years back that involved literally hundreds of rifles, all fired under the same conditions, same barrels, same everything right down the line. There was a very predictable and linear trend in accuracy related directly to case capacity, in all bore diameters across the board. In other words, 200 Win Mags were less accurate than 30-06s, which were in turn less accurate than 308s, etc.. Same thing in the 22s, where 220 Swifts were less accurate than 22-250s, which were less accurate than 223s, which were less accurate than 222s. Again, this test involved literally hundreds of guns, all built to the same standards, in the same shop, using the same barrels. The differences were often rather small, but the trend was clearly apparent. So in terms of the actions, where you're dealing with a larger cartridge in the long action, I'd expect to see a general reduction in accuracy. Same cartridge in both action lengths may be another matter, but I'd expect the differences to be relatively minor, if they could be discerned at all.
