A couple of weeks ago I posted a question about a problem I was having with FTE (failure to eject) from a 391. I appreciate the helpful responses.
To make a long story short, it turned out to be caused by dirty gas ports, even though I had carefully cleaned them
(or I thought I had). A hard carbon deposit had built up inside the ports, even though I had rodded them out with a stiff wire. I finally reamed out the carbon with a drill bit, and was amazed at the amount of carbon that came out. No more FTE. That's what I will be using to clean them from now on.
I found that a 7/64" or 1/8" bit will work. The 7/64 bit may be a little easier to use, but the 1/8 bit fits tighter and thus cleans better, but will not cut the metal if you turn it by hand.
You need to hold the bit with something other than your fingers, so you can twist it with a little force. I actually used a small electric drill the first time, but be careful not to cut any metal that way. I then held the bit with a small pair of Vice Grips and that works, but isn't real convenient. I found a Ryobi bit at Home Depot that is made to fit in a hex chuck, and that works fine. I also found that a standard 1/8" bit will fit in a scriber that I had (also available at Home Depot) with the scriber point removed.
Both bits are illustrated below. I plan to keep the Ryobi bit in "The Mother of All Gun Cleaning Kits" which I carry with me to all tournaments.