Jeese...
Who Cares? They are off the market... (but I would like to have one)
The pressures that you are quoting are impressive, and nearing Bolt Gun Pressures... While the barrels may well hold up to these pressures, the design limits of the lock up on a lever, given the thickness of the receivers, the battering that they would take at those pressures, an occasional failure would not be unbelievable..
I am not at all familiar with this EXACT model, but I own two other Rossi levers, in 38/357, and one in 44. Both are designed about the same.. I have shot some pretty bodacious loads out of both of them, but not a steady diet..
I'm not sure that either one of my guns would hold up under a steady diet of loads at the pressures you describe..
The bolt locking mechanism on the Rossi Lever, is really not all that different from the feature on the M-92 and 96 Beretta pistols, in that there are locking lugs that, in the Beretta, momentarily take the full brunt of the the recoil on the two lugs, that are riding in slots milled into the slide of the Beretta, an the receiver on the Rossi...
Cracking slides in the m-92's are well documented with +P ammo.. It is why SEALS used to have a a saying of "You can't be a NAVY SEAL until you have tasted Italian Steel". I too have seen the cracked Beretta slides come into the shop..
Not to say they are the same, but the lock-up designs share a similar feature.. and a constant hammering at near 55K cup of pressure, coupled with the inertia that comes off the thumb size heavy bullets that the Casull is capable of throwing... This would tend to lend credence to the belief that an occasional failure was possible...