Hold something in place solidly please!
I've wasted 5 rivets already... I think they are too long (they keep bending), but I've cut them at 1.5x the diameter of the rivet + the thickness of the materials. Maybe the leather isn't providing enough "support" for the sides?
If you do make a video, I'll be ever indebted to you!
M.
Okay, that one is somewhat easier than articulating.
If it's a domed head, it's best if it is sitting inside a dimple to keep it from moving around. Clip it off so that it is about as high above the washer as the diameter of the shaft, if not slightly less.
I like to clip mine off with a pair of bolt cutters. It leaves a nice "/\" on top.
I like to use a ball peen (domed head) hammer.
I like to start by tapping down on the outer edges at the top of the "/\". It mashes easily, and helps keep the washer held down in place.
After that, it's mostly a mushroom it out process. Once the washer is held down enough, work the sharp edge of the "/\" down a bit, then give the center of the rivet some solid smacks. That will swell the shank of the rivet so that it holds in place better. After that, keep tapping it down and "spreading" it a bit. What you want in the end is to "squish" the material out into something sort of like a countersunk screw head. Somewhat like "\=/", but where the top of it is flush. Just make sure you don't thin it out too much, or it won't hold as well.
I've seen some people say to make more of a "dome" on the inside too, instead of flat. I find flat easier, and I see flat on actual period pieces as well.
If they keep bending, it's likely they are too long. If it isn't that, then my guess is that it's not being held directly upright, and you're striking too hard and too far off center. I get bends when they are too long, primarily something like trying to go through canvas + steel + leather for shield strapping.