Primers in Starline 32-20

Being as the 32-20 cartridge is of smaller capacity than the 357 Magnum you might find useful information herein.

Comparison of various SP and SR primers in the 357 Magnum

Give the panic buying, hoarding and shortage of firearms, ammunition and reloading equipment and components several recent threads have asked if it is “safe” to use, in lieu of standard SP primers, magnum strength SP primers or even SR primers.  This question pops up every now and then but the recent numerous queries on this topic seem to be driven by the dire shortage of primers.  Some reloaders have no standard SP primers with no prospect of obtaining any in the foreseeable future at anything resembling a reasonable price.  They do, on the other hand have SP magnum or SR primers both of which fit the primer pockets of handgun cartridges using a SP primer.

 A recent video by a small ammunition manufacturer indicated switching from a standard SP primer to a SP magnum primer of the same manufacture posed no problem in the 9mm P cartridge with the given load tested.  They tested on the video two 3 shot test of that load to get three shot tests of pressure and of velocity.  While there appeared to a mild increase in psi and velocity when the SP magnum primer was use with that load the difference did not seem to be too much.  I had reservations about that as the test sample was too small and the load (powder and charge) was not given. 

 While I had not specifically tested a direct comparison between different types of primers I had, from previous chronographing and pressure measurements, formed an opinion that, while some switching of different makes and types of primers seemingly made little difference, switching primers can sometimes give sufficient differences, particularly in pressure.  I, of course, referring to small handgun cartridges using the faster burning powders.  The results of this test should in no way be construed as a blanket statement or rule of thumb.  There are just too many variables concerning the volume of cartridge cases and, probably most importantly, the ignition and burning characteristics of slower burning powders.  The results of this test apply to the use of the easily ignitable fast burning powders used in small handgun cartridges. 

Thus, to find an answer to the question [Can SP magnum or SR primers be substituted for SP primers in the smaller cartridge cases with a given load?]  I rummaged through my supply of SP and SR primers and came up with five different SP primer make/types to test;

CCI 500

Federal 100

Winchester WSP

CCI 550

Federal 200 Magnum

 I also came up with five SR primer make/types to test;

Remington 7 ½

CCI 400

Winchester WSR

Federal 205 Magnum

CCI 500

 While there are other such primers I feel a sample of 10 different primers should give us an idea of the potential pressure increases and some aspect of whether or not substituting primers might be “safe”. 

Thus with that selection of primers I prepped 100 Winchester 357 magnum cases [ten shot test with each primer] .  I selected a load to use with all the primers that was a mid-range 357 magnum load [based on previous chronographing] which should give a bit of “fudge” room if the psi’s did get too high with any primer.  The load I selected to use was 6 gr of Alliant Unique under a 358156 cast of COWWs + 2% tin, sized .358, Hornady GCs crimped on and lubed with BAC.  The bullets were seated, and roll crimped in the front crimp groove giving the loaded OAL at 1.597”. 

 

The SAAMI MAP for both the 357 magnum and the 9mm P are 35,000 psi.

The test firearm was my Contender 7.94” barrel with the strain gauge located over the chamber as per SAAMI specification.  The strain gauge was connected to the Oehler m43 PBL.  Test conditions were a reasonable 60 degrees with 30% humidity and little to no wind.  The velocity listed is muzzle velocity as the M43 corrects the screened velocity to the muzzle.  The Oehler Sky-screen start screen was 10’ from the muzzle. 

All results are based on the 10 shot test string for each primer. All the time/pressure curves (traces) appeared normal for the test firearm. The results are listed by primer.  Since the thrust of answering the question has to do with pressure that is the focus of this test.  I shall make comments after the data for each primer is listed and also in conclusion. 

 CCI 500 SPP primer

 Average velocity; 1178 fps, SD 11 fps, ES 38 fps.  PSI average; 25,700

 SD 2,100, ES 5,700, high psi was 29,200 and the low psi was 23,500.

This is a particularly good load.  The internals are excellent as shown by the low SD/ES of both velocity and psi.

Federal 100 SP primer

 Average velocity; 1189 fps, SD 10 fps, ES 36 fps.  PSI average; 27,900, SD 1,700, ES 5,500, high psi was 30,300 and the low psi was 24,800.

Another excellent load but we see a slight increase in velocity and psi.  The 11 fps increase in velocity equated to an increase of 2,200 psi.

Winchester WSP primer

 Average velocity was 1175 fps, SD 18 fps, ES 60 fps.  PSI average; 26,300, SD 3,400, ES 9,900,

high psi was 31,700 and the low psi was 21,800. 

This primer is supposed to be of stronger brisance as it is intended to ignite ball powders.  We see a velocity and psi comparable to the previous two primers, but we also see a much larger SD and ES of both velocity and psi.  Two of the tested rounds gave a psi above 30,000.

  CCI 550 SP Magnum primer

Average velocity was 1179 fps, SD 17 fps, ES 60 FPS.  PSI average: 27,500, SD 3,900, ES 13,500, high psi was 35,300 and the low psi was 21,800. 

This SP magnum primer showed no increase in velocity or in psi averages.  However, obviously the internal psi created with what was supposed to be a “mild” 357 magnum load of Unique demonstrates something is amiss here given the somewhat erratic internal ballistics.  Two the tested psi’s were above 30,000 with one exceeding the SAAMI MAP for the 357 magnum.  

Federal 200 Magnum SP primer

Average velocity was: 1176 fps, SD 14 fps, ES 43 fps.  PSI average: 27,100, SD 2,700, ES 8,800, high psi was 32,000 and the low psi was 23,200.

Again, this magnum SP primer gave no increase in average velocity or psi.  Yet the wide SD/ES of the psi measurements indicate somewhat erratic performance.  The 32,000 psi shot gives cause for concern.

 Remington 7 ½ SR primer

 Average velocity was; 1184 fps, SD 20 FPS, ES 78 FPS.  PSI average: 28,100, SD 2,800, ES 9,100, high psi was 32,000 and the low psi was 22,900.

 Except for the much larger SD/ES of the psi this SR primer gave similar performance to the Federal 100 primer.  We must note that two of the tested shots exceeded 30, psi with this primer but not with the Federal SP primer.  A noticeable difference.

CCI 400 SR primer

Average velocity was: 1188 fps, SD 15 fps, ES 52 fps.  PSI average was 29,200, SD 3,700, ES 12,200, high psi was 35,100 and the low psi was 22,900.

 Quite erratic yet the chronographed velocity does not indicate that.  No appreciable gain in average velocity yet a 2-3,000 psi gain is apparent in the average psi.  Five of the tested ten shots gave psi above 30,000 with one exceeding the SAAMI MAP. 

 Winchester WSR primers

 Average velocity was: 1173 fps, SD 17 fps, ES 50 fps.  PSI average was:  27,600, SD 3,800, ES 9,100, high psi was 32,600 and the low psi was 23,500 psi.

 Again, erratic internal psi yet not apparent based on the “normal “chronograph measurements.  No appreciable increase in velocity or psi as shown by the “average” of each yet 4 of the tested shots exceeded 30,000 psi. 

Federal 205 SR Magnum primer

Average velocity was: 1185 fps, SD 16 fps, ES 63 fps.  PSI average was: 29,700, SD 2,400, ES 8,200, high psi was 34,000 and the low psi was 25,800.

Again, erratic psi performance not belied by the chronographed velocity measurement.  Three of the tested shots exceed 30,000 psi with one approaching the SAAMI MAP.

CCI 450 SR primer

Average velocity was: 1171 fps, SD 15 fps, ES 47 fps.  PSI average was: 28,000, SD 2,400, ES 6,900, high psi was 31,000 and the low psi was 24,100.

No gain in velocity, small gain in psi with three of the tested shots above 30,000 psi.  Appears to be the mildest of the “magnum” strength SR primers tested. 

So there’s the data which brings us back to the question:  is substituting a SP magnum primer or a SR primer for a standard SP primer “safe” in a small handgun cartridge?  The answer is somewhat of a conundrum. If the load with the standard SP primer is a low or mid-level load then the substitution may be deemed “safe” depending on the actual case capacity of the load in question.  How do you know? 

 Unless you can measure the pressure, you won’t know.  Dropping back and working back up to the same chronographed velocity is often recommended.  I have even recommended that myself in the past.  But is that safe?  Looking at the velocities of all ten tested primers with the same load we find the average velocities ran from 1171 fps to 1188 fps, a spread of only 17 fps.  Interestingly the lowest and highest velocities of any of the rounds shot were with SR primers.  The average velocity variation falls easily within the average to average variation we can get chronographing the same load several times. 

Thus, chronographing really isn’t going to give an indication of the difference in psi.  The three standard SP primers averaged 25,700 psi to 27,900 psi with the highest psi of any individual shot being 31,700 psi.  With the SP magnum primers and the SR primers the psi was always higher with several of the tested shots exceeding the SAAMI MAP of 35,000 psi.  If we ponder what the highest tested shot psi’s would be (not the average of the test) if we had used a max load developed with standard primers in the 34-35,000 psi and then had substituted the standard primer with a SP magnum or SR primer?  The highest shot psi’s would probably have exceeded 40,000 psi.  That would not be what I consider to be “safe”.  Might get away with in in some larger framed revolvers but still not something to be recommended.  In a semi auto you might get away with it but it would beat the gun up at best and if a case head burst at the web.......possibly disasterous.

In the 9mm P with its much smaller case capacity?  I would not use any other primer than a standard SP primer.  With any other SR primer a "starting load" would be prudent.

LMG