06-23-2001, 02:20 AM
Join Date: May 2001
Leanwolfe, this is a pretty interesting article that I found on some benchrest site.
Rifle Primer Dimension Chart
Mfg Num CupCupCup
Thickness Diameter Height
Remington 6 1/2.020".1753".109"
Remington 9 1/2.027".2100".119"
I was getting primer piercing before I reached case overloading. I donít know what prompted me to try CCI 450ís instead of the 400ís which I had been using, but I did. Presto! No more piercing! Interesting!? A primer that has a hotter ignition and yet withstands more pressure! Thatís when I decided that it was time to do a dissection of all primers concerned. The chart above shows my results.
By studying the numbers, one can readily see which primers in the small rifle sections will withstand heavy loads. Primer cup diameters are all similar and appear to follow a specification, but check out the cup thickness in the small rifle primers (Dimension "A"). It is obvious that the thicker cups will withstand more pressure. Large rifle primers all appear to have the same cup thickness, no matter what the type. (As a note of interest, small pistol primers are .017" thick and large pistol primers are .020" thick.)
If you are shooting a 22 Cooper, Hornet, or a Bee, the .020" cup will perform admirably. But try using the .020" cup in a 17 Remington and youíll pierce primers, even with moderate loads.
Considering that cup thickness varies in the small rifle primers, it is obvious that primer "flatness" cannot solely be used as a pressure indicator.
Another factor which determines the strength of a primer cup is the work hardened state of the brass used to make the primer cup. They are made with cartridge brass (70% copper, 30% zinc), which can vary from 46,000 psi, soft, to 76,000 psi tensile strength when fully hardened. Manufacturers specify to their brass suppliers the hardness of brass desired. I was not able to test primer hardness, but an educated guess says that a primer manufacturer would choose a harder brass in order to keep material thickness down and reduce costs.
I have not run into primer piercing with large rifle primers. They are all the same thickness and therefore are not subject to the same misapplication problems. Exceptions can be created if too fast a powder is used in a magnum type case. The
22 Cheetah is a primer piercer with fast powders as Barry and I found out!
What does all this mean to the reloader?
Cases that utilize small rifle primers and operate at moderate pressures(40,000 psi) should use CCI 400, Federal 200, Rem 6 1/2, or Win SR. Such cases include 22 CCM, 22 Hornet and the 218 Bee. These primers are also used in heavy handguns such as the 9mm., 357, etc. Other cases that use the small rifle primer can use the above primers only if moderate loads are used. Keep to the lower end of reloading recommendations.
Cases that utilize Small Rifle primers and operate at higher pressures (55,000 psi) should use CCI 450, CCI BR4, Fed 205 and Rem 7 1/2.
With large rifle primers all being the same thickness, choose a primer that makes the most accurate group, is the shiniest, cheapest or whatever, as they all have similar pressure capabilities.
Hope this clears up some primer confusion. If you wnat more information about primers, priming compounds, or even how to make primers, the NRA sells an excellent book called "Ammunition Making" by George Frost . This book tells it like it is in the ammo making industry.
Any comments call: Jim at James Calhoon Mfg.: 406-395-4079.