I've tried a couple of products and tend to get good results except on the sharp edges. I boil and use #0000 steel wool and a 0.003" wire hand brush to card but still end up with a shiny edge. It's not as noticeable on larger pieces but really stands out on the small ones. Any thoughts? Thanks

Yes, don't scrub the edges.

try using just dry steel wool, no brush on the crisp edges.

Wet the corners a little more heavily and make sure they've really started rusting before boiling/carding. I tend to not let the first coat really bite sometimes and have this problem too.

The rusting compound will want to run off the corners unless the corner is facing the ground.

If your solution is running you are putting too much on.
I usually let the first coat work over night. at least.

I think you are carding too aggressively. I use a wheel from Brownells, item No. 360-164-631WB. I have no problems with bluing loss on edges of octagon barrels. Set it up in your drill press set up to run at a low speed and away you go.
Phil