There's nothing wrong with a Pietta brass frame .36 Navy, I have 4 of them. They are fitted well from the factory, are ready to go and they're tough, forgiving guns.
You can get them for about $250 new from anywhere that has them in stock. I shoot Pyrodex and anything from 1f to 3f real black in them, they accept CCI #11 caps and in my opinion the smaller charge and lighter ball of a .36 is easier on the brass frame. Get one to see if you'll actually shoot it alot and stick with Cap and Ballers, then you can add steel frame guns later.
If you shoot a brass .36 enough to "loosen it up" you've still gotten your $250 out of it, I have several hundred rounds through 2 of mine and they are as tight as when I got them. With 20 gr charges and balls. I've even tried conicals in them. I'd guess it would take a few thousand rounds of light loads to maybe start to loosen one up. Which honestly is probably a good few years of shooting if you shoot 50 rounds through it twice a month . And that's still WAY more than the average shooter will put through one. Most brassers are shot loose by people filling the chambers up with Pyrodex and crushing balls down. It's even said that loading is as hard on a brasser as shooting. I haven't seen any problems yet.
That being said I shot a steel frame Pietta loose in 2010 with max charges of Pyrodex P and Buffalo Bullets. The barrel wedge peened the slot and loosened the gun right up. I emailed Pietta and they said they don't harden the barrel steel and in broken English basically said, not to do that anymore with future Piettas. To be fair I was loading some of the bullets upside down which may have been bad. I was younger and dumber 12 years ago.
My Uberti .36 Navy survived the same charges and bullets and I still have it to this day, it probably has 2,000+ rounds through it.
Keep the charges within spec and you'll be fine. These aren't Magnums and never will be. The service charge of a '51 Navy was 18gr I believe.