I have taken to uniforming the primer pockets of rifle cases to make sure they aren't shallow - that's a direct result of the slam fire issues and an easy way to minimize one variable. I
That is one good step, I am going to state that reducing the risk of a slamfire is a series of steps as I have listed above. Sizing the case smaller than the chamber, getting the primer below the case head, and using the least sensitive primer you can. All actions with free floating firing pins are dependent on primer insensitivity to prevent primer ignition. All actions with free floating firing pins have incidental firing pin contact with the primer at some point in their cycle, designs such as the SKS, the bolt face is off axis until lock up, so slamfires in that action tend to be in battery.
Avoiding slam-fire on SKS?
https://www.thehighroad.org/index.php?threads/avoiding-slam-fire-on-sks.244071/
Murray's sells a firing pin modification kit, which includes a spring which reduces the impact energy of the firing pin on bolt closure:
https://murraysguns.com/sks-firing-pins/
The Italians made Garands for the Danes, and I assume, had their own.
When the Italians adopted the Garand based BM rifle, they modified the bolt mechanism by adding a spring. Obviously this is to reduce the inertial impact of the firing pin on a primer
As can be seen in the picture, I sent my NM Garand bolt to Roland Beaver and he added a spring.
I don't know by how much it reduces firing pin impact energy, I think it is all to the good, but still, put a round in the chamber, drop the bolt, and this is what the primer looks like
Literally millions of shooters have chambered rounds, seen the dimple left by the firing pin, and never pondered why the primer had not gone off. Also, millions of users never shook the bolt and listened to the firing pin rattling around, nor turned the action upside down to see what in the action was holding the firing back. There is nothing holding the firing pin back. Everyone assumes something is, but they never looked. This rifle came out in 1936. eighty three years, and yet generations of shooters have never examined the mechanism to see what keeps the cartridge from firing if the trigger is not pulled. What keeps the cartridge from igniting is primer insensitivity.
I can't find my notes when I talked to CCI when they first introduced the CCI #34 primer on the market, but it was around 1999. This primer is CCI's military primer, what they use on military contracts, and the average primer is a little less sensitive than a commercial primer. On the average. It turns out, primers vary considerably in sensitivity, and sometimes, surprises happen
http://news.yahoo.com/blogs/sideshow...232052308.html
By Eric Pfeiffer, Yahoo! News | The Sideshow – Tue, Jun 12, 2012
A Pennsylvania woman was shot in the leg while shopping at a local department store on Tuesday. But in a nearly unbelievable twist, no gun was involved. Apparently, the woman was carrying the bullet in her purse, when it mysteriously exploded.
"She did not have a gun in her purse or on her," Montoursville Deputy Police Chief Jason Bentley told the Williamsport Sun-Gazette. Bentley said the woman, whose name has not been released to the public, "was not aware" she was carrying two or three bullets inside her purse at the time of the accident.
The 56-year-old woman was taken to a local hospital and was eventually discharged. In fact, the woman initially declined medical treatment, only heading to the Williamsport Regional Medical Center after her son reportedly encouraged her to do so.
"Something must of hit the primer of one of the bullets," Bentley said. "The bullet stayed in the purse, but its casing put a hole in the purse and caused a minor leg wound."
Bullets exploding outside of a gun are a rare occurrence but are not entirely unprecedented. In March, a bullet being used as evidence in a court case exploded in a bag and shot 20 feet across a courtroom. No one was hurt in the incident. It was surmised that the bullet exploded after its tip bounced against another bullet tip in the same evidence bag, according to the Telegram & Gazette.
Slamfires happen even with military spec primers because priming compound varies in sensitivity within the batch. Some primers in the same lot are more sensitive than the others. There are test limits, but you know, they only test about 50 primers at the low energy drop test. How do you know that all primers in the lot, and that lot is probably hundreds of thousands of primers, are above spec limits? You don't, all the manufacturer can do is statistical tests which predict lot sensitivity.
Everyone has had a dud primer, an insensitive primer, so shooters believe in insensitive primer. But if the primer goes off, how do you tell if it was a sensitive primer? Shooters therefore don't observe primer sensitivity and don't believe what they don't see. (that is until you shoot Bullseye Pistol rimfires and find some brands ignite but others stove pipe or fail to eject, or cut coils on pistol mainsprings) But sensitive primers exist in all primer batches which is why there are reports of slamfires with military ammunition. But, the most sensitive primers are commercial primers, particularly Federal primers, and when I use to ask shooters about slamfires, the common thread was Federal match primers. Federal makes the most sensitive primer on the market and used to be proud to advertise that. Federal also makes a mil spec primer and supposedly introduced it for small rifle primers, but have never seen one.
There are construction differences between commercial primers and mil spec primers, and this post is accurate:
Magnum Primers in Standard Cartridges
https://thefiringline.com/forums/showthread.php?t=594411
Ron, here are the differences in the 2 primers. So the anvil angle change is the difference, this keeps the free floating firing pins from causing slam-fires in AR style platforms. This does make it so that a light strike will have a less of a change of going off.
CCI-250............................ Magnum primer, Mag primer mix, thick cup, standard anvil.
#34/7.62MM................... Mil. Spec. primer, thick cup, magnum primer charge, angle of anvil change.
By using a thicker cup, increasing the distance between cup and anvil, and changing the anvil tip shape, and varying what is in the primer compound, manufacturers alter primer sensitivity.
Reloaders should copy the dimensions of a new military round, by small base sizing, and priming the case with the least sensitive primer they can, and never orient the rifle vertically down when single loading. That little extra added acceleration due to gravity has caused a lot of AR15 slamfires, and Garand slamfires.
The NRA forbid reloading on the stool when AR's started replacing M1a's. When you shot slow fire standing, with an M1a, you had the butt of the rifle on the stool, you pushed a round in the magazine, tripped the bolt. The muzzle was pointed at the sky and I never heard or saw a M1a slamfire in this orientation. But, the AR shooters started placing the muzzle on the shooting stool, put a round in the chamber, tripped the bolt, and reports started coming in that rounds were going through shooting stools. Now you can't load or rest a loaded rifle on the shooting stool.