.......BUT a topper barrel is not a barrel I would chop. I would chop a modern 30-30 barrel with no guilt what so ever.......
I agree 100%. The nice, older slender barrels are not easy to find. I would have no compunctions about shortening a newer one.
I have a newer 30-30 barrel and it's a shame that it is so beefy. With a 22" barrel on the break-open action it's not terribly long overall, but the thought has crossed my mind to cut it down to reduce the weight some. Wouldn't be a consideration on a Topper.
The 30-30 is a very versatile cartridge with brass fairly easy to locate. Outside of the "normal" 30-30 loadings, I have loaded Sierra 110 grain HPs to shoot pretty flat and 165 grain cast to shoot pretty quietly. I have not read up on the AAC so I don't know how versatile it is in comparison.
If you have other 30-30s, and handload, you have the components and dies already. Shortening a newer 30-30 to play with cast, sub-sonic, Handi(er) configuration might be a cheaper and easier way to scratch that itch. I am not advocating or suggesting being practical here - just a quicker, easier route to your entertainment objectives. I have guns I have no practical use for but they are fun to play with.