A friend brought his new (used) pistol over to show me yesterday. He was pleased with the good price he got it for off of Gunbroker, but he said the bore looked a little odd to him.
It's a Walther P22. The bore indeed looked funky, especially the last 1/2" or so. It has a thin inner barrel and an outer barrel bushing. The barrel is threaded at the muzzle and held on by a nut. He took it apart and I noticed that the threads looked very odd. Instead of clean, fine threads like you normally see on a firearm, this had rough 1/4-20 threads obviously cut by hand with a die. It was so bad that the threads had pulled on the inside of the muzzle.
This gun comes with either a longer barrel and "slide extension", or a shorter barrel and normal muzzle nut. I expect someone decided to just cut their longer barrel and crudely thread it themselves, to where the rough, coarse threads kind of jam into the fine threads in the muzzle nut. I told him he should contact the seller, but he just said the listing made it clear as-is, no returns.
Live and learn; at least a new barrel isn't terribly expensive. I'm not a big fan of buying things like that sight unseen.