Piece 4, Flash hole size effects, errata

[joeb33050]

We have some data points on the flash hole diameter vs. pressure vs. velocity spectrum.
Bass Ackwards tells of a velocity change with enlarged flash holes.
Mooman 76 did a test with a M93 Mauser in 7MM
Larry Gibson has explained several loads he shoots with enlarged flash holes. (Where is Larry? I keep asking him for permission to use what he wrote, and no response.)
TRK, who is going to scan and send it to me, quotes Phil Sharp about pressure and velocity tests with enlarged flash holes.

I can't measure pressure, don't shoot 30 jacketed bullets a year, shoot low velocity cast bullets. I'm going to make sets of cartridge cases with flash holes enlarged with a #28 drill, and measure velocities with standard vs. drilled flash holes. I invite others to do the same. Maybe we'll get results like Larry's, where accuracy improved and SD went down. ONLY low velocity loads, we don't want a gun blown up here.

Errata: The Fouling Shot, Jan-Feb 2007, "Velocity Check" by Grant Macomber mentions velocity increas from 1300 to 1330 to 1400 fps mean velocity with changes in primer only.

Something's going on here with flash holes and primer choice and primer strike force, and maybe there's an easy and cheap accuracy enhancer hidden in the stories.

joe brennan

[Char-Gar]

Joe..Keep up the work as I am interested in the outcome. I have a lot of 30-06 cases (LC 67 NM) with the pockets drill with a No. 28. I have only used them twice and have noticed no change in accuracy either way.

I may have to dig out the chrony. It has been put up for 15 years.

[Larry Gibson]

Larry Gibson has explained several loads he shoots with enlarged flash holes. (Where is Larry? I keep asking him for permission to use what he wrote, and no response.)
TRK, who is going to scan and send it to me, quotes Phil Sharp about pressure
joe brennan

Joe

Assuming you got my messages, I was at Camp Lejeune, NC training Marines from the 16th through the 31st. They were mostly 12-16 hour days out in the GIZRA (SP?) (don't ask me what it stands for - it's a Marine thing) or at the MOUT site. I will be going back on the 10 Feb for another 8 days. Trying to catch up on all the message traffic here and, of course "honey do's".

Larry Gibson

[44man]

I also think there is a lot to it but be sure you keep those enlarged flash hole cases away from hotter loads! Reminds me of the time a customer brought out a cheap muzzle loader with a nipple that had a large hole in it. Thing would cock the hammer and send pieces of cap into his face. A nipple change fixed it. You see what even low pressure black powder loads can send back! I dread the thought of putting 50,000 or more pounds of pressure into that hole if it is too large.