I posted before I saw your reply, so here are my thoughts on barrel fitting.
I've traded for barrels on this forum, and have bought or traded four barrels, and out of the four, only one fit like it was made for my receiver, and one fit but wouldn't lock up, so I was able to take off a tiny amount from the breech face, and it locks up and shoots like it was factory fitted to my frame.
The other two I had to add shims, and it's a little bit of work to get it right, and I've had good results, but now it's a wait and see, to see just how long it holds up.
I'm not into shooting paper on a regular basis, so I'm thinking that with as much as I shoot those barrels, I should be good for a long, long time.
That said, it does take some tinkering skills, and basic mechanical aptitude to get it done properly, and I wouldn't recommend it if you are just a little skeptical about your skills.
If I were contemplating buying/trading for a used barrel and not done it before, I would buy/trade the barrel, and if it doesn't fit exact, or is loose, I would immediately put it back up for trade rather than tamper with it, and thus give someone else a chance to booger it up, if they so choose to do so, and if you trade it, the one you trade for may fit your receiver and then if it again doesn't fit, I'd just sell it outright and recoup what I can, and order a barrel fitted by the factory.
In other words, if it don't fit I'm trading it, and give someone else a chance, because 50/50 to me isn't good odds.
If you have more receivers, the chances are better for a proper fit, but I've only got two, and those are my odds, which aren't that good.
It's a roll of the dice, and doing a good shim job takes a little work, and some don't seem to mind, but I don't think it's worth the trouble, because a perfect fitting barrel makes life and accuracy a whole lot more enjoyable. But that's just my opinion!