I do it for all my rifle brass, but I don't know why. Probably because my brother said he does it and it's a good thing. Cartridges have been going BANG for a helluva lotta years with burrs around the flash holes. Pain in the butt, but ya only gotta do it once.
Ever feel like the world's a tuxedo, and you're a pair of brown shoes? - George Gobel
What Lefty said. The basic all too elusive one hole group of 10 shots at 100 yards or more is theoretically possible if everything, and I mean everything, is exactly the same shot after shot after shot after shot, etc. Those who pursue this goal spend a great deal of time and effort in trying to make sure the volume inside each case is the same, the primers blow the same amount of flame, the powder is exactly the same, the bullets are exactly alike and seated to the exact same depth, and so on. I used to shoot with one guy who used a runout gauge to find and then mark the high spot on his rounds. I think he would have spun balanced them if he could have found a little machine to do that, too. He had a self made solid aluminum stock with a 40XB action, 2 ounce trigger, ultra heavy barrel and all the other tricks that were around 35 years ago. His rounds looked like jewels because he polished them - not just cleaned, polished.
He still didn't shoot a whole lot better than everyone else, but he had fun trying.
Uniform flash holes certainly don't do any harm, but how serious are you about the rest of your case prep routine? Do you weight sort them? Group by length, headstamp, age, number of firings? Measure neck thickness? Inside and/or outside turn the necks? Check finished rounds for concentricity? Use match bullets? Match primers?
ALL who work for a living must vote to outvote those who vote for a living.
out of 4 rifle calibres i shoot now none shown a improvement after deburring. yet still i do it because there always the possibility.even if i'm just hunting i'd hate to know my shot could be off because of something "i" didn't do.
besides...isn't that the whole point of reloading...to make something better and cheaper than factory???even if the target doesn't know it??
I uniform the primer pocket and uniform the flash hole from the inside. I do this on every brass only once. Another tid bit for ya, military brass I've been reloading needs additional processes like outside neck turning that the commercial stuff does not require.
Well, there are pocket uniformers that cut to a specific diameter and depth. There are flash hole deburing tools that remove ragged edges of the punched holes and chamfers them a tad. Some debur tools will simultanously ream the flash hole to a standard diameter. Then there are dedicated flash hole uniformers that simply drill the flash holes to a uniform diameter.
IMHO, anyone hoping to improve consistant 3/8" or so groups may see some small accuracy benefit to doing all that. (I do it all but I KNOW I'm just fanning the wind!)