20 grains in a 44 ought to last a real long time. What eventually happens is the back of the cylinder dents into the frame and opens up the cylinder gap. I looked at a brasser 44 Remmie at a shoot once that was for sale with a "make offer" tag on it. The gap had to be about .015 and there was a perfect footprint of the back of the cylinder in the frame. I'm not sure how much stretching there was (had to be some) but the indentation of the recoil shield was obvious. Once the gap opens up a bit the cylinder has longer to travel before it slams into the frame so it hits harder and harder each time. I'm guessing the bolt held the cylinder close enough to fire the cap but then the cylinder is knocked forward a bit (closing the gap) but then slides back under recoil. So once the loosening begins it progresses faster.
With over 15 perCUSSIN' revolvers, I've been called the Imelda Marcos of cap & ball.
SASS#3302 (Life), SASS Regulator, NRA (Life), DGB#129
Wolverton Mtn. Peacekeepers (WA), former Orygun Cowboy (Ranger, Posse from Hell)