I've done the remill work using a jeweler saw. I a lite stroke in each groove. It's not hard, but is very time consuming. That was twenty years ago. I now just put a full sheet of 400 grit wet/dry sandpaper (soaked for 10 mins or more) in a coffee can, the ruff side facing in, and swirl the coin so it "rolls" arounds in the can. Do that for 30 seconds and see if you find it easier to palm. Done right this makes micro impressions in the coins edge and doesn't really remove any metal ( it gives a kind of satin feel to the edge). It works well for me. You can change the grit and the amount of time to suit your needs. Be gentle with silver coins and I wouldn't do this with a gaff coins. For shells, I wipe them down with alcohol and then rub them against a small block of violin rosin (about $3.00 at most music stores). I find this improves my ability to palm coins.

Use a slitting needle file and be gentle

Hello, boydy, do you use a specific size? there appears to be large range of sizes available.