I have done a few.
Lever actions on Marlins and Winchesters both. Most were in 30-30 with a short and a long barrel, but one was done with a 7-30 Waters 24" long barrel and an 16" 30-30. I have 2 take down waiting for work now, but neither one is going to be a "swap-caliber rifle".
I also did one for a man on a Browning M95 in 270 and 35 Whelen one time. Last year I did a swap barrel on a Savage with a 22-250 and a 300 savage.
Several on Mausers. Probably 20 or so. In fact I have one in the works now, with a 9X57 and a 257 Roberts front end. 2 barrels, 2 for-ends, 2 scopes and both reloading dies in the set. The 257 Roberts scope is set up for the standard mounting on the action, and the 9X57 is set up for scout mounting on the barrel. And the 9X57 has an "American twist" in that the barrel uses .358 bullets instead of the German standard .356", so loading ammo is super easy.
I have done them in both standard bolt face and magnums. Combinations have been from 6MM Remington to 9.3X57 and from 264 Win Mag to 338 Win Mag. One I did for a Navada man was a 270 and 35 Whelen. One I did for a Texan customer was a 300H&H and a 375H&H
One rifle that is often overlooked that has shown me it can be quite accurate and strong is the Browning BLR, Take-Down, but I don't know if Browning is offering 2 barrels in 2 calibers from their custom shop or not. Might be worth a call to ask. The BLRs with forward mounted scopes have shown me MOA accuracy quite a few times.
