Mossberg has no plans of offering other calibers at this time. They said that in the future they might offer other calibers though. It is rumored that Virgin Valley Custom Guns
www.virginvalleyguns.com will make barrels in other calibers for the SSI if enough people request it. The H&R is a very solid rifle, but not the best fit and finish. You have to send the reciever in for fitting to get a new barrel. As for the Ruger #1 and the TC, I think they are fine rifles, but I would consider the SSI as an equal to these fine guns. The SSI has excellant fit and finish, very well balanced and is more accurate out of the box than the average rifle. I have talked to several gunsmiths who have had to tweak the #1's to get the accuracy my SSI .270 had right out of the box. Of course, the TC is known for its accuracy.
P.S. Has anyone else with a single shot heard these questions regarding you're rifle;
What do you do if you miss and need a second shot?
What are you going to do if you wound a deer and it starts running?
Why would you want a single shot?
Makes me want to laugh - Later, BigAL