I can't help you with your first question but I am curious as to why you would ask that?
Had you read or heard something saying 180's were too much for the gun?
I would think that as long as the ammo is SAAMI spec it would be safe but, now that you have my curiosity piqued, I'm looking forward to the answers too
As to your second question, "stiff" is subjective from person to person but the .44 mag SBH I owned wasn't "stiff" but rather what I'd consider "positive", it clicked open or closed with very distinct movement.
My .22 Single Six might be characterized as slightly stiff but I think it has more to do with the fact that the loading gate is much shorter than that of my SBH, ie. less leverage, and that's what makes it feel stiff.