All the above are good reasons for a swamped barrel, but if you look at the swamping dimensions in Alexander's book on originals, you will see there isn't a whole lot of swamp to them. 1/16" is pretty common. You can kick out the tails of the lock by filing the bolster. That is'd done a whole lot, but it CAN be. With an A-weight barrel, a standard Large Siler has too thick of a bolster to achieve a thin look in this area, so it needs it. I took as much as .060" off on my last build, and stopped when the RR started nicking the main spring.
Also, in favor of the straight barrel is increased stiffness. With a thin waist and wider muzzle, the whippier part of the barrel will be in the middle, and with more mass out front, the amplitude of the barrel oscillations will be greater, making them intrinsically less accurate. It's trickier to work up the correct load with swamped barrels than straight or tapered ones. Most of the target rifles today (cartridge and otherwise) are made with relatively short and thick straight barrels. Some .22 rifles even have extension tubes for the front (iron) sights. The longer the projectile takes to get from sear trip to muzzle exit, the more chance there is for the muzzle to be pointed somewhere else than it was at sear trip.
