How does the Winchester Model 100 compare to the BAR and 7400 as a pig gun?

The .308 Win cartridge will perform as well from any of the rifles you mention. Accuracy will depend on the individual rifle and the particular ammo you're using. At pig hunting distances, it should not be an issue.

The M100 Winchester is, in my opinion, as reliable as either the Remington or the Browning. On the other hand, the Browning will probably have the nicest finish, followed by the Remington, with the Winchester having the most utilitarian finish. It's not ugly, but it's a shooter, not a showpiece.