I did get some responses from shooters on the "Flash Hole" and "Prime" issue and no matter what I post someone will challenge it so instead of the information I post you can make up your mind on what is or isn't better. I saw Testing done where it was thought at the 0.062 was better for some Competition Cartridges with a Small Primer Pocket and after the testing was done for ES & SD it was concluded that the Standard 0.080 Flash hole was better in both the Large & Small Primer Pockets.
Prime Manufactures did not respond to my request on information.
I did get a response from CAPSTONE GROUP on Lapua Cases with why the have both the Lrg & Sm primer Pockets and 0.0660 & 0.080 Flash Holes. Now Capstone's results were contradicted by several shooter in the field doing independent tests. So you can make up you make up your own mind by doing some research.
Some questions to ask yourself. If the 0.060 Flash hole works better in Competition type Caes - Why not use it in everything????
Hello Leonard,
Thank you for contacting us at Capstone PG. You ask a very good question. To start, it will be easier to start by listing the cartridges that we make that do use the small rifle primer pocket with the 0.060" diameter flash hole. These would be the following. .220 Russian, 6.5 Grendel, 6mm BR Norma, 6.5 X 47 Lapua, and .308 Winchester Palma. All of the other sporting rifle cases offered by Lapua will use either small rifle or large rifle primers as specified by SAAMI or CIP dimensions and use the 0.080" flash hole dimension as standard for them.
What had started the use of the smaller 0.060" diameter flash hole goes back to the start of PPC series of cartridges that have been based off of the .220 Russian parent case. It had been found in testing that the smaller diameter flash hole gave much smoother pressure rise for a given case design as compared to the use of the larger diameter of 0.080" flash hole as shown in pressure testing by the late Dan Pollack. Dan had found in this testing that the smaller diameter of the 0.060" flash hole had focused the flame front of the primer ignition to a much smaller diameter as compared to the use of the 0.080" flash hole. He went on to explain that this narrower flame front in essence bored a hole through the powder column and would ignite the powder charge almost in the middle of the powder column and gave this very smooth gradual pressure rise which had proved itself in the consistency of the groups fired with the .22 PPC and 6mm PPC cartridges early on. Dan said that the best way to explain this is that this emulates the use of a extended primer tube that is used a lot in heavy munitions such as what might be used in cartridges like the 105mm tank round and is actually emulated in the 30mm ammo used in the A-10 ground attack aircraft with a primer that is longer to begin with instead of being a part of the construction of the case as had been done in the past for when the primer would be seated into the back of the case and would feed the flash tube directly.
The other benefit that Dan had seen is that if we could use as cool of a light up of the powder charge to get reliable ignition that we could see additional improvements in the grouping and precision of the cartridge. Based on these early findings from Dan, further research has shown the benefits found with the small rifle, small flash hole configuration would benefit larger case designs and that is the reason that we offer this primer pocket configuration.
In removing any found burrs, simply use an appropriate tool just knock the burr off with a minimal bevel on it. We hope that this information answers the question that you had.
