In part one of this series on primers, we looked at that the
different primers are and what the primer actually is. In part two, we will be
getting more in depth and looking at how the primer selection can affect your
How a primer affects your load
Primers affect the pressure generated by the cartridge.
Changing from standard to magnum primers may substantially raise the maximum
average pressure of the cartridge and indiscriminate changes are not
recommended. The A-Square Company conducted pressure tests involving six
different primers. These tests used the 7mm Remington Magnum cartridge with a
160 grain Sierra BT bullet and 66.0 grains of H4831 powder and the results were
reported in the A-Square reloading manual
Any Shot You Want. A-Square
used CCI 200 and 250, Federal 215, Remington 9 1/2M, and Winchester WLRM and
WLR primers in these tests. They revealed a total spread in pressure of 12,800
psi from the mildest standard (the CCI 200) to the hottest magnum (WLRM) primer
Changing brands, but using the same type of primer will also
usually result in pressure changes, but ordinarily these will be less drastic.
In the A-Square tests the pressure spread between the CCI 200 and the hottest
standard primer (the WLR) was 9600 psi. The spread between the mildest magnum
Rem. 9 1/2M) and the hottest magnum primer (WLRM) was 8300 psi.
These are significant pressure variations that cannot safely be disregarded.
Incidentally, these same tests revealed that the Federal 215
and CCI 250 large rifle magnum primers produced nearly identical pressures. The
difference between these two primers was only 100 psi. A-Square also reported
that, while they had not tested these two primers in all possible cartridges,
this result was typical of their experience with these two primers.
It’s a good idea to follow the recommendations of whatever
reloading manual you are using as a reference regarding the proper brand and
type of primer to use. For example, if the load in the manual was developed using
a WLR large rifle primer, then that is what I use. If one brand of primer (of
the same type) must be substituted for another, the conventional wisdom is to
reduce the recommended powder charge by 10% (assuming the load is not already
at the minimum) and work back up slowly.
Seating the primers
When reloading, always seat primers slightly below flush
with the head of the cartridge case. This insures that the anvil is properly
pressed against the priming compound for reliable ignition. Failure to properly
seat primers is the biggest single cause of misfires in reloaded ammunition. A
good depth to aim
.005" below flush. With some experience this can
be determined by feeling the case head after the primer is seated. Any primer
that is flush or protruding should be
very carefully removed
and the case reprimed.
Decapping a live primer can set the thing off, so behave
accordingly and take all necessary precautions, including ear and eye
For hunting and general recreational shooting purposes I have
not ordinarily seen a significant difference in accuracy attributable to using
different brands of primers. However, there are exceptions to this general
loads seem to work better with a certain primer. Sometimes
chronographed standard deviation in the velocity of a load is lower with
one brand of primer than with another. In such cases I just go with the flow
and use whatever primer works best.
Modern primers are a marvel of ingenuity and production
uniformity. The importance of these little cartridge "spark plugs" is
often overlooked by recreational shooters--in itself a tribute to their