John
Cartridges of the World claim that the 350 No 2 is just a flanged version of the 350 Rigby Rimless Mag but I think this is not correct.
If you can get a look at a 350 No 2 and a 350 Rimless Mag and put them side by side you'll see that they are quite different in case size and capacity. The 350 No 2 actually uses the same case as the 400/350 Rigby. The 350 Rigby Rimless Mag uses a case which has a larger diameter at both base and shoulder.
Graeme Wright mentions in his book Shooting The British Double Rifle, that the 350 No 2 is not the same as the flanged version of the 350 Rigby magnum.
I believe the 350 No 2 is just the 400/350 loaded with a lighter bullet. 225 gn instead of 310 gn.
What I am really trying to find out, is, does a Flanged cartridge actually exsist which has the same dimentions as the Rigby 350 rimless mag.

As to these cartridges being good in a double, guess what my most used, go anywhere double is chambered for.
Although the 400/350 was a flanged cartridge and mainly used in doubles, Rigby also produced a bolt gun chambered for this round. Very nice too!
Alan