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Flash Hole Deburring
- Thread starter ninosdemente
- Start date
JeepHammer,
I completely forgotten the flash hole size , good advice .
LBMR: as in 'long before most reloaders' Herter offered a tool for sale that measure the diameter of the flash hole. In the early days there was a small chance of finding a flash hole that was small in diameter. For reloaders that measured before and again after there was a greater chance the flash hole increased in diameter when fired. At the same time shell holders were offered to reloaders, one brand sold was RCBS, RCBS shell holders fit the case head like a hand-me- down shirt, the case only fit the shell holder where it touched (those were and are my favorite). And then? There were shell holders that fit the case head, RCBS shell holders had as much as .012" clearance between the deck of the shell holder and case head; the other brand was less forgiving meaning when forming cases the RCBS shell holder had all the advantages.
Back to the diameter of the flash hole: I have loaded rounds with the 'good' fitting shell holders that would not fit the shell holder after firing. It was about this time I started using the small gasket cutting ball peen hammer to drive cases into my good fitting shell holders. The cases would not fit the shell holder because the case head was upset with heavy loads. The diameter of the flash hole increased, the case head thickness from the cup above the web to the case head decreased and the case head diameter increased.
Again: While helping form cases for a wildcat chamber I checked 460 belted cases; 40 of the belted cases would not fit the #4 RCBS shell holder, the builder of the wildcats asked me to bring 'the other #4 shell holder'. Instead I furnished the gasket cutting ball peen hammer. The 40 belted cases would not fit the RCBS shell holder because the case heads were upset/crushed.
F. Guffey
Ninosdemente,
I have encountered a couple of examples of deburring flash holes helping over time.
Twenty-five years ago, my M1A's original barrel would shoot 0.7 moa consistently with my handloads built with IMR4895 and 4064, Brigadier 3032, Reloader 12, and a few other stick powders I tried. One year I decided to try Accurate 2520 because, being a spherical powder, it metered well. My groups opened to 1.2 moa and would not tune down. Then, on a whim one day, I tried deburring flash holes and the 2520 groups shrank to 0.7 moa same as the other powders. Knowing more now, I might have got the same result going to a magnum primer, but that barrel is long sice shot-out, so I can't make the retro-comparison. I can only say it was apparently the case that deburring flash holes helped a harder-to-ignite powder work up to its potential. Of course, I then went back to stick powder hoping for a similar improvement, but saw none. 0.7 moa was being limited by the gun or the shooter's ability with iron sights and the long, heavy trigger at that point.
Another instance is with once-fired crimped primer brass. I use the Dillon 600 swaging tool to remove crimps. It backs up the head of the case with an anvil on the inside while swaging the crimp out. I discovered that the anvil can bend the flash hole burrs over the hole, obstructing it. This is an inconsistent issue, but one that occurs often enough that I have to watch for it. I either have to drill such holes clear or deburr before running them through the tool.
I have encountered a couple of examples of deburring flash holes helping over time.
Twenty-five years ago, my M1A's original barrel would shoot 0.7 moa consistently with my handloads built with IMR4895 and 4064, Brigadier 3032, Reloader 12, and a few other stick powders I tried. One year I decided to try Accurate 2520 because, being a spherical powder, it metered well. My groups opened to 1.2 moa and would not tune down. Then, on a whim one day, I tried deburring flash holes and the 2520 groups shrank to 0.7 moa same as the other powders. Knowing more now, I might have got the same result going to a magnum primer, but that barrel is long sice shot-out, so I can't make the retro-comparison. I can only say it was apparently the case that deburring flash holes helped a harder-to-ignite powder work up to its potential. Of course, I then went back to stick powder hoping for a similar improvement, but saw none. 0.7 moa was being limited by the gun or the shooter's ability with iron sights and the long, heavy trigger at that point.
Another instance is with once-fired crimped primer brass. I use the Dillon 600 swaging tool to remove crimps. It backs up the head of the case with an anvil on the inside while swaging the crimp out. I discovered that the anvil can bend the flash hole burrs over the hole, obstructing it. This is an inconsistent issue, but one that occurs often enough that I have to watch for it. I either have to drill such holes clear or deburr before running them through the tool.