I can’t say I’ve ever noticed mine being gritty. I had issues with my 835 (and 590 I think) when they were brand new, like less than 100 rounds through them. They were stiff to cycle and the 835 didn’t always want to unlock to open the action. It was really frustrating, but I haven’t noticed it in quite a while now. The 590 as I recall had no problems after a very short break in cycle.
What kind of lube do you use? I’ve never used anything high end on my shotguns, usually some light oil. Even just 3 in 1 oil. But I am now looking into trying out slip 2000 or the Lucas gun oil.
This next statement may ruffle feathers, and I can’t speak from experience, but I was recently told by a Sig Sauer rep that frog lube is terrible. I have no idea why that is and a lot of people use it. To me, it seemed like there was too much work involved to use it. But I have no idea what would be bad about it.