Primer cake is mixed by hand, heard the workers have paddles. Primer cake formulas vary, look at George Frost's Book Making ammunition.
The legacy military small arms primer mix is the FA 956 mix,
PATR 2700 Encyclopedia of Explosives Vol 8 gives the composition
FA 956
Lead Styphanate 37.7 +/- 5%
Tetracene 4.0 +/- 1%
Barium Nitrate 32.0 +/- 5%
Antimony Sulfide 15.0 +/- 2%
Aluminum Powder 7.0 +/- 1%
PETN 5.0 +/- 1%
Gum Arabic 0.2%
Do notice that there are allowable in mix percentages. Given the plus or minus and the differences in purity, it can be seen that primer cake varies by lot. Have a shooting buddy who was a gauging expert and went to Government ammunition plants. Bud claimed workers are given financial ncentives if their batch of primer cake is the most consistent. Probably some of the parameters measured are dwell, peak, duration , energy, and temperature. Bud said material ejection was measured. Even though workers are incentivized, just who makes the most consistent primer cake turns out to be, as bud said,
"an artifact". Which means, by chance.
There are plenty of primer compositions for there are many applications for primers other than small arms. This is a list of military priming mixtures, FA 70 is the old corrosive primer, I was able to identify PA101 as a fuse primer composition. All of the compositions to the right of FA90 are more sensitive than rifle primer compositions, so these are probably used on a variety of explosive or propellant devices.
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I have used CCI, Winchester, Federal primers for decades, just purchased the cheapest stuff. I did get made at Winchester when Winchester went to their brass finish primers. They made the primers more sensitive by using a thinner cup. The brass finish WSR pierced and ate AR15 firing pins at loads that never bothered the nickle plated WSR. However, the CCI 41 primer has a thick cup and shoots extremely well. I do use brass WLP and WSP, high sensitivity is a good thing in my pistols, I seldom shoot high pressure magnums anymore so I am not worried about primer piercing. Pistols have weak ignition systems compared to rifles so real sensitive primers such as Federal or Winchester are just fine with me, if the price is right. Still, if your pistol has a weak mainspring, time to replace it!
This round was fired in a M586 that the first owner had shot over 60,000 rounds in PPC competition. He used Federal primers. In cold weather, with AA#9, a ball powder, weak ignition caused a squib and luckily the bullet lodged in the barrel throat, preventing the cylinder from turning. If it had gone further up the barrel, I could have bulged the barrel with the next shot. I had to drive the bullet back into the case with a long shafted standard screwdriver.
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Primer looks well hit, but that was illusory
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I replaced the old mainspring with a new one, no squibs to date, pistol shoots fine
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Politics and lobbying by big business have removed Russian primers from the market. I am sad about this as the Tula primers I purchased are some of the best rifle primers I ever used, they were unusually consistent.
I have been buying primers by price for more than a half century by now, my advice is to use the mil spec primers in semi auto rifles as those things are prone to slamfiring with sensitive commercial primers. You have a slamfire, best case is that you will be startled. Commercial primers are not appropriate for Garand mechanisms, this rifle slamfired out of battery with S&B factory ammunition. It is obvious that the primers were too sensitive for this mechanism.
View attachment 991033
https://www.reddit.com/r/guns/comments/8czy2h/m1_garand_blew_up_in_my_face/
The only appropriate primer to use in Garands/M1a's are the mil spec primers, that is CCI #34's. Commercial primers, all commercial primers, are more sensitive. Even then there are out of battery reports with CCI #34 primers, and that is because primer cake sensitivity varies by lot, and within the lot. The mil spec primers are less sensitive on average, but, that does not mean that there will not be sensitive lots of mil spec primers.
Other than that, while I have seen differences in velocities over my chronograph between brands, I really don't know if it is due to the brand, or is due to lot variance within the brand. I don't recommend Winchester brass finish rifle primers due to their propensity to pierce, but I am shooting them up with mid range loads. Federal primers are the most slamfiring rifle primer around, so I will not use them in Garands or AR15's, but they shoot just fine in bolt guns and single shots.
