First I'd buy it in a minute as most every cartridge is available or there is a way to make usable brass. Bullets can be cast, paper patched or resized to fit almost any bore.
I shoot a nice little drilling in 16ga(2 1/2")/6.5x58R Sauer. I have to cut to length and resize 9.3x72R brass down to the 6.5x58R and resize 6.5(.264) jacketed bullets down to .260. It is a great drilling and it is my go to coyote hunting gun. It is well worth the effort, in fact the effort makes it so much more satisfying to hunt with.
Savage 99 with my drilling I can take on just about anything that walks, flies or swims on this continent from my shoe laces to 250 yard without having to do anymore than push the safety off. Take your Ithaca and troll it over at the BP thread and explain that they just don't know what they are doing and your pump will do everything an old BP gun can do, maybe some one there will give a c--p.
By the way I love hammers for hunting.