I discussed this project with my gunsmith this am. In a Handi, an AI rechamber will actually be an AII or Ackley Improved Improved because the barrel can't be set back as in an action with a threaded barrel. What this means is the chamber will be slightly longer and factory ammo can't be fired in it without taking additional case forming/fire forming steps. For me, since I won't be using factory .280 ammo, but will be using Nosler .280AI brass, I will probably need to, but not necessarily, have to seat bullets into the rifling on the first firing to keep the case from being knocked forward when the firing pin hits the primer.
He does .35WhelenAI rechambers for Alaskan hunters that want all the powder capacity they can get, so he doesn't set the barrels back for them, so they end up with an AII chamber.
His recommendation for me, once the brass if fired once, just to neck size when reloading for it.
As soon as I get the brass and dies, I'll make a dummy round up and send it along with the barrel to him for rechambering.
Thanks to all who contributed to this discussion!!
And thanks to Fred's web page for contributing in his absence!!
http://www.angelfire.com/ma/ZERMEL/280AI.htmlTim