Hi,
There are many factors involved with barrel leading, including bullet size, alloy hardness, powder "speed" (as related to chamber pressure) AND barrel condition.
There's an old rule of thumb to figure if you're generating ENOUGH pressure to obturate lead bullets well enough: multiply your lead alloy's hardness (BHN or Brinnell Hardness Number) by 1422 (often rounded to 1400 for convenience/ease of memory.) The resulting pressure is a rough minimum required to bump up the bullets adequately.
For example, we have a .38 Spl bullet with a BHN of 10, which multiplied by 1422 gives us 14220. So we'd want a load that generates at least 14,000 psi of pressure for that bullet to behave well. That same size and weight bullet, only cast with a different alloy at a BHN of 18, times 1422, gives us a min number of 25,596. So in a .357 Mag loaded to at least 25,500 psi, it should work ok, but likely wouldn't do so well loaded at .38 Spl pressures.
'Tis just a rule of thumb, but helpful for "eyeballing" numbers in your reloading recipes...
Rick C