There is an endless debate as to what primers are best to use in 9mm major.
1. Some argue that small pistol primers are not good because they have the thinnest cup (relative to small rifle and small pistol magnum) that may lead to piercing and create a dangerous situation. However, reloading manuals for the 9x23, 38 super, 357 sig which are all high pressure rounds call for small pistol primers.
2. Others argue that small pistol magnum are no good because they raise the peak pressure at the same velocity (remember a bullet's speed is a measurement of an average pressure over the time the bullet is in the bore). You can achieve the same average by a taller pressure peak that eases off relatively quickly, or a small peak and higher constant pressure. However, they have thicker cups that can handle magnum pressures.
3. Others argue that small rifle is the best because it has the thickest cup period.
Make the long story short, I think small pistol magnum primers are the best because:
1. Small rifle primers create a higher peak than small magnum primers based on the powders they were designed to ignite, noticeably slower than any pistol powder. These always require a stronger spark, which yields to a higher peak, which is what we're really trying to avoid. Additionally, because of the thicker cup, you don't see any signs of over pressure.
2. Regular pistol primers, while do have lower peak pressure do have thinner cups that may result in piercing, although I've never had one pierce on my 9mm major loads. You could argue that these are the primers to go for based on pressure peaks, but a lot of our 9mm major loads are close to compressed, which requires more spark to ignite - remember that in reduced volume with lower contents of oxigen, ability to burn powder is really on the power of the spark (in this case the activation energy)
3. The reason why I choose small pistol magnum primers is because there is a compromise. Additionally I've done some measurements on the primers coming out of a 9mm major gun. All things equal, the findings are very interesting. Before I mention the findings, I think that it's important to understand how primer flow and catering occurs. When you fire a high pressure load, there is forward pressure that pushes the bullet out, this same pressure expands the brass to create a seal in the chamber, but it also pushes through the primer hole on the primer. When the pressure is so great, the primer is pushed out of the primer pocket, but the breach retains it. Catering occurs due to this pressure pushing the primer cut through the firing pin hole. Primer flow occurs because the mouth of the primer pocket is beveled, hence the pressure molds the base of the primer to this bevel. In normal pressure no catering and no primer flow occur. Now to the measurements... for each primer type measure the thicket part of the circumference of the primer after it's fired... for small pistol its 1.77, small pistol magnum 1.75, and for small rifle it's 1.73 . These are measurements of 10 brass casings - interesting the standard deviation in all three cases was 0 - that tells you the high tolerance of primer pockets (rightfully so). The primer pockets all measured 1.72 - this being extremely interesting... we have all read that 9mm major rounds expand primer pockets, this proves it's not so... none of the primer pockets were expanded over regular pressure rounds of 1.72.
Now, if the thickest part of the fired primer is thicker for small pistol and small pistol magnum, doesn't this mean that you have a better seal against gases going around the primer relative to small rifle primers? At the end of the day, I don't know, but it can't be worse to have a better seal by the base of the primer conforming to the bevel of the primer pocket...
Therefore, based on peak pressure, primer seal from deformation, and middle of the pack primer cup thickness, I choose small pistol magnum primers. Second I would choose small pistol primers based on the above. Rifle primers have to many against (higher peak pressure, thicker non sealing primer cups, lack of pressure read...)
Some additional info:
Primers tested:
Tula, Federal, and CCI small pistol magnum - ALL measured 1.77 at the base after being fired
Federal and CCI small pistol magnum - ALL measured 1.75 at the base after being fired
Tula and CCI small rifle primers - All measured 1.73 at the base after being fired.
Brass was mixed, but all had same primer pocket diameter
7,6gr HS6 pushing 124 FMJ
6.7gr Win248 pushing 124 FMJ
8.7gr 3N38 pushing 124 FMJ
All three loads are between 170 and 175 PF - all primers measured the same regardless of load (very interesting)
Test Gun: CZ Czechmate
Hope this helps....
