Of the 13 rounds that failed to fire in the Kimber 84M, all but 2 fired in the Rem 788. Firing pin strikes by the 788 were definitely stronger. The the bullets two rounds that failed to fire were pulled, the powder emptied and the primers removed. Upon inspection of the primer, there is no apparent reason for the primer not to have fired
You make have cracked the primer cake first strike but not set off the primer. Than the next time, no primer cake between anvil and cup.
I reamed the pockets of my LC79 too deep and primed the cases with CCI #34 primers, which are less sensitive mil spec primers. After reaming these pockets extra deep, I take that ammunition to a 1000 yard match and try to shoot the stuff in my match M70. I got lots of misfires: click and no bang. I had at least 20 misfires, and the ones that went off, well I am going to blame my poor groups on poor ignition. Much easier to blame the ammunition than a lack of shooting skills and wind reading ability.
So, here is one of those cases that did not go bang when hit by the firing pin of my M70. Looks like a good hit. But it was not, the primer was too deep, and it was already a rather insensitive primer to begin with.
After the match I decided to measure the depth of the primers below the case head of those cases that misfired.
Primer seating depth on CCI #34 primers in LC79 308 cases that misfired in M70
0.004
0.004
0.004
0.005
0.005
0.005
0.006
0.006
0.006
0.008
0.008
0.008
0.009
0.009
0.009
0.009
0.01
0.011
0.012
avg depth 0.007
N = 19
Next local 100 yard reduced match, I decided to shoot that ammunition in my M1a. The basic Garand mechanism has a very powerful ignition system and plenty of firing pin protrusion. The ammunition picture, the tall cases are some of the pre struck M70 ammunition, the short cases are pre struck M70 cases that went bang in the M1a chamber. At least I did not have to pull the cases down, and that M1a had more than enough energy to make these pre dimpled primers ignite.
While I still ream pockets, I no longer ream to crazy depths.
This post by Hummer 70 is worth reading.
IT DON’T GO BANG-FIRES, HANGFIRES, MISFIRES AND SHORT ORDER COOKS
http://gunhub.com/ammunition/42928-don-t-go-bang-fires-hangfires-misfires-short-order.html
Basically what Hummer70 is pointing out is the lack of knowledge, technical competence, in the firearms industry. Cost cutting has removed core technical competency and knowledge in the Commercial sector, and in my opinion, core technical competency and knowledge was been gone for decades from the US Army Ordnance Bureau. So what you get is poorly designed ignition systems that fail to ignite cartridges because the designers don't know about the energy characteristics of primers.
Even highly reverved designers, have their limitations. Eugene Stoner designed one heck of an interesting rifle in the AR series, but he was clueless about primer sensitivity.
Icord report page 4560
Mr. Stoner. Well, yes, because I knew that the rifle was, you know, was going to be used by the armed service and I wanted to make sure that we had adequate background on it before we went into it. Because the history, and all the testing that was done with the IMR propellants. We had another thing that happened on the Marine Corps test that went with that. We had some inadvertent firings of the weapon due to the primer that we were using. We were using a commercial primer in that round which is relatively soft and sensitive, and the Marines, on their firing, on their known distance range, would single load the weapon. They would put a round in the chamber and then let the bolt go home by pushing the closing button on it or the bolt catch, and the inertia of the firing pin would fire the weapon sometimes this way.
It was a very low frequency, but it did happen. So, of course, they wanted something done about it, and the Army found out about this. There were a couple of solutions. Either desensitize the primer, make it out of a thick material, or lighten up the firing pin. Well, what I recommended was lightening up the firing pin because I didn’t see-if you desensitized the primer too much it could cause failures to fire in the field.
In other words, we wouldn’t have enough energy to fire the primer under all conditions. And I-in this technical data package they decreased the sensitivity of the primer at the same them they went in and put the ball propellant in. So these were two things I objected to with Mr. Vee.
Here again, I didn’t know what the effects would be because we didn’t have all this test data, I mean testing, behind us that we had on the other ammunition. While the design on the firing pin, to lighten it, which was subsequently done by Colt, was a relatively simple thing, and in my opinion, wouldn’t detract from the performance of the weapon any. As I say this weapon was tested for years and years and before this inadvertent firing ever come up and it come up because probably we had a batch of ammunition where the sensitivity level on these primers were on the low end, or, I should say, the high end of sensitivity, and also, the fact that there were firing the weapon in a way that they formerly didn’t before, which was single loading, when it was an automatic weapon.
Usually the weapon was loaded from the magazine and when the rounds were stripped out of the magazine like it was intended to be used, this slowed the bolt down enough that you didn’t have the impact velocity to cause an inadvertent firing.
There were actually two things that I took exception to on that. I didn’t sit in on the Board that came up with the ammunition specification. I wasn’t asked to. I am not in the ammunition business. But, I have a good deal of interest in the ammunition due to the fact- usually you can’t change the ammunition without causing a change in the performance of the weapon.
Besides verifying that the early M16's slamfired, what Stoner claims is the real problem, that the USMC was not using the weapon properly, because they were not always firing from the magazine, is in fact, pure hogwash. A user should be able to drop a round in the chamber without having the mechanism slamfire. The M16 procurement revealed that the Armalite and Colt Organizations did little in examining the technical performance issues of their rifle. In this case, Stoner only knows about primer sensitivity as a conceptual basis. He does not know how much energy is required to ignite an average primer, and he does not know the kinetic energy of his firing pin. It turns out, if you study this, the kinetic energy of his early firing pin was always above the "none fire" limits of commercial primers. None fire is a very important safety criteria: no primer is supposed to ignite when hit by a firing pin whose kinetic energy is less than the "none fire" limit. Stoner's design, the primers were always being hit by a firing pin whose kinetic energy exceeded the "none fire" limit.
Stoner does not accept any responsibility in this: he considers his design perfect. It was far from perfect, it was in fact an immature design that was not ready for combat.
It turns out, he still did not learn from this experience. His Stoner 63 series of rifles
https://en.wikipedia.org/wiki/Stoner_63 had a severe misfire problem. His ignition system did not sufficient energy to reliably ignite the #41 primer used in Government ammunition.
