process, but it's really pretty simple ... you put a taper into the muzzle of the barrel by removing the lands of the rifling in the first inch or inch and a half of the barrel.
IF your tool is concentric to the bore, there will probably be no effect on accuracy. All of the tools I have used or seen to do this are a fairly gentle taper, and you put wet/dry sandpaper on the cone with double sided tape and simply hand turn the thing as a mandrel holds it centered in the bore and concentric with the axis. You can go to finer grits of abrasive and end up with a super smooth finish if you like. (I took mine to 1200 grit and stopped there, mainly out of boredom - it loads and shoots with no effort - you can start the ball and patch with thumb pressure.)
There are two types of tool. The first is a caliber specific, made by Joe Woods. Joe is located in Texas, here:
Joe Woods
5311 Briar Street
Amarillo TX 79109
(806) 352-3032
The second is a 'universal' type tool - you can do more than one caliber. A fellow on this site makes them, and much to my chagrin I cannot recall his name. Apologies, unknown tool maker. I'll try to find the contact info... There is a fellow named Ed Hamberg (sp?) 1008 Logan, Alton IL 62002 who also makes this type of tool... to use this one, you put a cleaning jag with a lubed patch on it, and this is what holds the cone in axis with the barrel and the sandpaper cuts the cone. I have never used this type of tool, so I can't attest to its efficacy. I would see no reason that such a tool would be any better or worse (assuming the directions were closely followed) and it would have the advantage of allowing you to cone barrels of different caliber if you were so inclined.
As to the effect on accuracy; I am of two minds. Some barrel makers rant and rail against the process, and say it will ruin your barrel forever, that it's unnecessary, that it will make your hair fall out, your private parts shrivel up, and so on... Other barrel makers say that it probably doesn't hurt. but here's my take on it:
(1) I'm not that great a shot anyway, and I haven't shot for the X-ring in many years, so a minor variation in barrel consistency would show up if I were the shooter ... I'm just not good enough to worry about minute of angle... minute of Bambi?... heck. am I in the right zip code?
and
(2) since I'm not trying to "pot the ace at a mile," whatever makes the shooting more fun, or easier, will probably encourage me to use the rifle more often, thus increasing my trigger time and shrinking the prospective group through the magic of practice... (and WOW - if you could sell the "magic of practice" by the quart, you'd be a zillionaire!)
to do an actual scientific test, you would need a blind random sample, with control groups of more than 32 subjects ... one side coned, one side not coned, with as many variables as possible (weather, shooter error, the phase of the moon, etc.) completely eliminated ... this whole deal would be prohibitively expensive (you would need a sample set of thirty two coned and thirty two unconed barrels, and a boatload of individual shots, and so on, to be 'statistically reliable,' and then you'd have to buy all the powder and shot, and then you'd want to have the barrels shooting as well as you could (think Dutch Soultz' method writ large) and AAAAARRGH!! it makes one's head hurt just thinking about ...
so we default to anecdotal evidence: it works for me, or "I knew a fellow who's girlfriend knew someone who said..."
as for my opinion: go for it.
good luck with your project!