Please don't rechamber. Try RST, they specialize in 2 1/2" shells for vintage guns. www.rstshells.com
That's kind'a the way I'm thinking anyway. One of the people who suggested measuring the chambers before assuming they aren't re-bored is Scott from Scotts Gun Smithing. But then he also suggested a rechamber if they aren't.
The RST shells look quite a bit cheaper than the Kent Shells which Cabela's supposedly has for around $16 a box. 10 or so boxes of vintage-compatible (short) shells would likely be a couple years or more of shooting as I don't expect to shoot it very much and it may well cost $10 - $12 or more a box even for 2-3/4" shells. One thing I would like to find is a box or 2 of #5 in 1 oz or even better yet, 1-1/8 oz 2-1/2" shells. That would tempt me to take the thing Pheasant hunting over dogs
Edited:
A cursory look around tells me these RST shells are cheaper than most 16 2-3/4 shells around anyway. I can shoot a flat or so then get a cheap reloader to reload the hulls. Might even tempt me to buy a vintage shotgun sometime down the road in 16 ga since that's the classic European gauge anyway.