Comparison of various SP and SR primers in the 357 Magnum

[Larry Gibson]

Comparison of various SP and SR primers in the 357 Magnum


Given 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 tests of a 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 used with the same load the difference did not seem to be too much. The factory rep so stated it was safe to substitute primers. I had reservations about that conclusion as the test sample was too small and the load (powder and charge) was not given. Now he could have done that test numerous times to get a valid test sampling but that was not apparent from the video.

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 450

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 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.

[B]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. But then, 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 other than a "starting load".

[M-Tecs]

Larry thanks for the very detailed and informative post.

[Markopolo]

wow... well there goes that theory!!!!

nice work Larry

[onelight]

Very interesting , thank you for posting and doing the tests .
It would be interesting to know if a slower powder like 2400 that is often loaded with both standard and magnum primers would show similar results .
I have compared velocity of some 9mm loads with ( BE-86 ) both magnum and standard primers same load except for primers , and we decided there was not much difference 50 to 70 FPS , now I know we have no idea what was going on pressure wise.
Thanks again.

[Flailguy]

Thank you Larry for the information! I would have never thought there could be that much variance in pressure without change in velocity.

[Ford SD]

With the SAAMI MAP of 35,000 psi. did any of the over presure loads are any of the primers showing visible signs of overpressure ?

Q
if we started at min loads and worked up .. do you think we would have problems

Most of my shooting is just putting holes in Paper and I very rarely shoot near max

When I was shooting IPSC was the only Time I pushed it was in the 40 but the primers never showed any excessive signs (reg pp)

Practice was a low to med load of a different powder

I do have some CCI SR that I had Planed to shoot in 38 special / 357 target loads

switched to SRM for all of my 223 / 300 bo ar Loads .... harder primer

Thanks for expanding our knowledge base

[dverna]

Very well done

BTW, I always cringe when someone alludes to using a chronograph to check the safety of a load. Anyone who believes that should read Larry’s post until they understand it.

One small point Larry, did you notice any discernible differences in primer deformation when there were 10k+ differences in the same load?

[dale2242]

Nice work Larry.
The test is up to your usual high standards.
Very few of us have pressure testing equipment so the chronograph is not telling us when the pressure is high.
I always assumed that if the pressure increased the velocity would show it. Guess not.
I have always thought the flatness of a primer was sign of pressure.

[Larry Gibson]

dale2242

None of the primers exhibited any sign of excess psi. All the fired primers were very similar in appearance. Flatness of primer can be an indication of pressure if the cartridge to chamber headspace is not to great. that is when the primer backs out initially then is flattened as the case is driven back over it to the breach face. Also consider the flatness of the primer indicates psi only. The primer may appear to be flattened from "high pressure" but that's not necessarily the case. A primer with a softer cup will flatten more than a hard cup primer giving the appearance of excessive psi when, in fact, the psi is within normal limits for the cartridge. That's why primer flatness/appearance is no longer considered to be a reliable indicator of excessive pressure.

[dtknowles]

Larry, thanks, excellent work as always. I had stayed out of the primer substitution discussion because I had very little data. The one data point I had was improved accuracy from substitution of small pistol primers in .22 Hornet. This is reinforced by your results, small charges of power don't seem to ignite as uniformly from larger primer charges. The rule of thumb seems to be use a strong enough primer but not too strong. I only sort of agree that you can't tell with chronograph results. The clues are there, the erratic ignition shows up as greater extreme spread and standard deviation for the stronger primers. You would not notice unless you had a good bit of old data to compare to when changing primers.

I don't think substituting primers is dangerous, not dangerous like a double charge anyway. If you are someone who loads to max. you should probably back off if you switch primers.

Your data is awesome as it gives us better understanding of the relative strength of each primer.

I am not surprise by the lack of a velocity increase, the hotter primer does not add much to the total energy if you assume all the powder burns in all cases. These are either great loads you are a very fine handloader as these in my experience all these es and sd's are small.

Tim

[Larry Gibson]

Ford SD

With the SAAMI MAP of 35,000 psi. did any of the over presure loads are any of the primers showing visible signs of overpressure ?

No. As mentioned to dale2242, the primers all appeared essentially the same. Given proper headspace primer "flatness" does not really manifest itself until pressures get much higher.

Q
if we started at min loads and worked up .. do you think we would have problems

Note the load I used was a "mid range" 357 magnum load with average psi in the 25 - 28,000 range no single rounds psi exceeding 31,700 psi. With some SP magnum and SR primers the average psi increased 2-3,000 +/- psi with many of the individual rounds psi near or exceeding the SAAMI MAP of 35,000 psi. Do I think you will have problems? I think, if you must use SP magnum or SR primers is small capacity handgun cases, that I would just go with the "starting" load and call it good. At least you're still shooting that way. Working up higher than a start load, probably depending on the cartridge, could get into unknown high psi's very quickly.

Most of my shooting is just putting holes in Paper and I very rarely shoot near max

When I was shooting IPSC was the only Time I pushed it was in the 40 but the primers never showed any excessive signs (reg pp)

Practice was a low to med load of a different powder

I do have some CCI SR that I had Planed to shoot in 38 special / 357 target loads

All sounds good.

switched to SRM for all of my 223 / 300 bo ar Loads .... harder primer

I also use WSR or SR magnum primers in my 223/5.56 loads because of the ball powders I load with. Also the pressure levels for the firearms [ARs, bolt guns and SSs] run up into the 56 - 62,000 psi range. That rifle cartridge was made for those pressure levels. I don't shoot the 300 BO but shoot a bajillion 30 Carbine rounds. The use of standard SR primers [7 1/2s, WSRs and CCI 400s with top end H110 loads under cast or jacketed bullets works well. With sub-sonic loads using Bullseye powder a standard SP primer gives the most uniform velocities. Same in the diminutive 22 Hornet case, a SP primer works best giving the most uniform velocity and psi's with all powders I normally use [Bullseye, Unique, 4227, H110 and Lil'gun].

Thanks for expanding our knowledge base

You're welcome, my pleasure

[Larry Gibson]

dtknowles

"These are either great loads you are a very fine handloader as these in my experience all these es and sd's are small."

Well, I certainly like to think I have, over the many years, become "a fine handloader". But, alas, the smaller ES and SDs in this test had more to do with the load used (it's generally been proven to be a fine mid-range 357 magnum load) and the test firearm. The closed breach of the Contender almost invariably gives more uniform ES and SDs than revolvers do with their attendant longer cylinder throats and barrel/cylinder gaps. But.....I certainly like to take credit......:drinks:

[Larry Gibson]

Very interesting , thank you for posting and doing the tests .
It would be interesting to know if a slower powder like 2400 that is often loaded with both standard and magnum primers would show similar results .
I have compared velocity of some 9mm loads with ( BE-86 ) both magnum and standard primers same load except for primers , and we decided there was not much difference 50 to 70 FPS , now I know we have no idea what was going on pressure wise.
Thanks again.

This may answer your interest;

Test of Hercules and Alliant 2400 powder (14 gr each) in the 357 Magnum with a 358156 GC’d cast bullet using 6 different primers.

All measurements were taken during testing conducted on 29 April, 2019. Data recorded with an Oehler M43 PBL using Contender 357 with 7.9” barrel. A 2 ½ power scope was used on the Contender.

Temperature ranged from 80 to 82 degrees.
Humidity was 30%.
Barometric pressure was 29.63.

H2400 = Hercules 2400 manufactured in ’92.
A2400 = Alliant 2400 of current manufacture (purchased 2 months ago)
Velocity in fps is at muzzle.
Velocity SD/ES is fps.
PSI is the pressure (pounds per inch) recorded via the Oehler M43.
PSI SD/ES is the pressure (pounds per inch) variation of the test string.
Group = target at 50 yards with ctc measurement of 2 widest shots.
All test strings were 10 shots.

The 358156 were cast in a Lyman double cavity mould.
Alloy was a soft one made of RL + Pb + tin.
Bullets were AC’d 10+ days before size/lubing and BHN runs 10 – 11.
Bullets as cast are .359+ and were size/lubed in Lyman 450 with .359 H&I die.
Lube used was BAC.
Hornady GCs were seated in the 450 with GC seater prior to size/lubing.
The bullet weight, fully dressed, was 162 gr.

All charges of both the Hercules and Alliant 2400 were 14 gr (+/- 0.1 gr).
All test charges were thrown charges with a Lyman 55.
Charges were verified between each 10 charges thrown on an Ohaus 10-0-5 scale.
Cases were Winchester brass cases.
Cartridges were loaded using RCBS dies on CH press.
Primers are as indicated.
Bullets were seated to 1st crimp groove (the 358156 has two) for an OAL of 1.597”
A heavy rolled crimp was applied.

Looking at just the H2400 data it would appear the old adage of “magnum primers not necessary” does apply. The average velocities between the various primers, standard and magnum, were found to be pretty consistent. The pressures are also consistent and all fall under the SAAMI MAP for the 357 magnum cartridge. However, the accuracy of the magnum primed loads was consistently better than the standard primers with the exception of the WSP primer with the A2400 powder.

Looking at just the A2400 data we see pretty much the same consistence except the Alliant 2400 does appear to be somewhat faster burning than the older lot of Hercules 2400. In my previous testing I was using a lot of Alliant 2400 I purchased about 12 years ago. There was not the difference between that older lot of A2400 and the H2400 that we see here. Note also that this lot of A2400 consistently produced better accuracy than the H2400 regardless of the primer used. Interesting the highest velocity (1607 fps) and highest pressure (41,600 psi) produced the smallest 10 shot group. Additionally with standard primers the CCI 500 and WSP primers produced psi’s right at the SAAMI MAP. The Federal 100 produced a psi 3,400 more than the SAAMI MAP.

Comparing this lot of A2400 to the old lot of H2400 shows a decided difference. This lot of A2400 is obviously faster burning giving 90 to 160 fps (+/-) difference depending on the primer used. The SAAMI MAP for the 357 Magnum is 35,000 psi and we see in Lyman CBH #4 the max load of 2400 with a CCI 550 primer is 14 gr. Looking at the test results the pressure with that load using H2400 is under the SAAMI MAP. But the pressure using this new lot of A2400 with the same load and same primer is 39,000…..well over the SAAMI MAP.

So let’s answer the questions;

“Would it make any difference using these primers with Bullseye, Unique, and Red Dot ?”

Based on the large increase in psi over standard primers in this test it would appear the use of the Federal magnum SP primer would probably increase the psi significantly. If you really want to use those magnum primers then I suggest you drop the charge of any of those powders by 2 gr and work back up the same velocity as produced with a standard primer.

“No Magnum primers with Hercules or Alliant 2400!” ………… “You are probably safe with Hercules 2400, but not Alliant 2400.”

Based on this test it appears neither of those statements are quite correct. The use of a magnum primer and the WSP consistently proved more accurate than the standard primers with the same load. The remaining question seems to be if the load of A2400 is reduced to the SAAMI MAP Using any of the magnum primers will the accuracy be as good? Remains to be seen.

---Primer---------Powder----- Velocity----SD/ES-------PSI-----------SD/ES---------Group

Federal 100--------H2400--------1425-------13/44-------31,000-------1500/4500-------5.45”
----------------------A2400--------1572-------16/46-------38,400-------1200/4000-------5.1”

CCI 500-----------H2400---------1452-------12/41-------29,200-------1800/5200-------4.95”
----------------------A2400--------1551-------15/39-------35,400-------1500/5100--------4.87”

Win WSP---------H2400---------1425-------16/60-------26,200-------2000/6900--------5.2”
---------------------A2400---------1536-------14/49-------34,800-------1200/4300--------3.75”

Federal 200------H2400----------1481-------11/38-------32,100-------2500/6600--------3.7”
Magnum---------A2400----------1566-------15/46-------38,900-------2000/5800--------3.15”

CCI 550----------H2400----------1457-------11/37-------30,300-------2500/8900--------3.6”
Magnum----------A2400----------1581-------17/51-------39,000-------2100/6400-------3.55”

Winchester-------H2400----------1446-------22/67-------39,500-------2300/7000-------3.9”
WSPM------------A2400----------1607-------12/37-------41,600-------2700/9000-------2.85”

[Outpost75]

Outstanding work Larry, as always.

I am looking forward to a future project we exchanged email about in loading the .32 S&W Long in +P to establish a safe loading limit for modern revolvers like the S&W Models 30 and 31 and also for use in revolvers chambered for the .32 H&R Magnum. I expect that with the small case at high loading density primer choice may also be significant there.

[onelight]

Wow great information also in your post #13 thank you again Larry.

[Screwbolts]

Nice work Larry, You have the CCI 500 primer listed as both SP and SR. They are SP primers. just a clerical mistake I am sure.

Ken

[reddog81]

Much better info than the three 3 round tests done in the "recent video". Not only was that a very small sample size, but he got one round that was like 20% higher pressure than the others and says that it should just be ignored! When you do a very small sample and get an outlier like that, it should not just be ignored. Like your testing shows a 20% variation in pressure can happen and does happen.

[Larry Gibson]

Nice work Larry, You have the CCI 500 primer listed as both SP and SR. They are SP primers. just a clerical mistake I am sure.

Ken

Thanks for the catch. That was under the primers to be tested. Should have been a CCI 450 primer (corrected). The test data was correct listed under the CCI 450 SR primer.

[Larry Gibson]

Much better info than the three 3 round tests done in the "recent video". Not only was that a very small sample size, but he got one round that was like 20% higher pressure than the others and says that it should just be ignored! When you do a very small sample and get an outlier like that, it should not just be ignored. Like your testing shows a 20% variation in pressure can happen and does happen.

Excellent and correct observation!

[Larry Gibson]

Some expressed interest in the flatness of the primers so here's the primers left to right columns as tested;

276345

[charlie b]

Thanks Larry!

The data actually makes sense to me, given the load used.

I had always understood that the mag primers were intended for high load density powder loads (especially ball powders), which is kinda what Winchester implies with their primers. A bit more oomph for their line of powder. Using a mag primer in a lower load density should result in erratic ignition. I would expect the same from SR primers in pistols of lower load density.

By the same token, using std primers in high density magnum loads sometimes results in erratic velocities.

Too bad you don't have an 'expendable' barrel to use for such a test (high load density), since if there is an issue you would be far above safe levels. :)

The data is a great warning about using mag and rifle primers in many pistol applications.

[jeepyj]

Larry, Many thanks for such an Informative collection of information. With the current shortage situation I hear the primer question on a regular basis at the local LGS. I generally stay out of the conversation but listen with interest. This post has help me greatly with my understanding. Your patience and thoroughness of your answers to each of the questions presented is also a big help. Thanks again, jeepyj

[megasupermagnum]

Thank you very much for another great comparison Larry. These tests are always informative, and very much appreciated.

I will disagree slightly on your stance of not using large rifle primers. I look at that data, and I don't see a huge difference from a safety standpoint. According to SAMMI, the max average pressure is 35,000 PSI for 9mm Luger. SAMMI also describes maximum extreme variation as 4% standard deviation (MAP * 0.04) * (5.16) = MEV

I guess 5.16 was plucked from some unseen table, but they say it applies to all calibers. 35k * .04 = 1,400 and 1,400 * 5.16 = 7,224

So according to SAMMI, the pressure spec on standard 9mm Luger is 35,000 PSI + or - 7,224 PSI. That means according to SAMMI, a single sample of up to 42,224 PSI is of no concern, and meets their criteria for safety.

[dougader]

Excellent work Larry. Thank you for taking the time and sharing it here.

[JeffG]

Great information Larry. Thank you.

[Larry Gibson]

Thank you very much for another great comparison Larry. These tests are always informative, and very much appreciated.

I will disagree slightly on your stance of not using large rifle primers. I look at that data, and I don't see a huge difference from a safety standpoint. According to SAMMI, the max average pressure is 35,000 PSI for 9mm Luger. SAMMI also describes maximum extreme variation as 4% standard deviation (MAP * 0.04) * (5.16) = MEV

I guess 5.16 was plucked from some unseen table, but they say it applies to all calibers. 35k * .04 = 1,400 and 1,400 * 5.16 = 7,224

So according to SAMMI, the pressure spec on standard 9mm Luger is 35,000 PSI + or - 7,224 PSI. That means according to SAMMI, a single sample of up to 42,224 PSI is of no concern, and meets their criteria for safety.

The MEV [Maximum Extreme Variation] is not a +/- figure. It is based on the SD of the "population" [that is the SD of the load tested] x the constant of 5.16. Quoting the definition from SAAMI: "The MEV is the maximum allowable sample E.V. (Extreme Variation or range) is a statistic derived from the knowledge of the population Standard Deviation." Thus, unless you know the actual pressure SD of the load tested you can't compute the MEV. The use of the MEV formula is to compare the SD to the ES of the measured pressure of a given population (load) which ensures the pressure variation is within normal computed variation. Note the MEV by being computed based on an SD and compared to the ES it is based on an "average" figure, not based on individual shot pressures.

I'm not sure where you come up with a constant SD of "7,224" for the 9mm?

As a general statement I would not "conclude" individual shot pressures of 42,224 psi [if that figure were correct] in the 9mm P to be of "no concern". In some handguns designed for those psi's, perhaps. However, in smaller handguns w/o integral feed ramps that may not be a wise combination. You may be getting away with it with the load and specific primer you are using in the firearm you are using it in but to say or insinuate such can be used as a general rule is not something I derive from the actual test data. Ergo, I would have some concern.

However, the question was not "can you use" but was a question of "can or should you substitute SP magnum or SR primers safely". Two different questions with most probably two different answers. Answering the question based on the actual test data I will stand by my previous conclusion; if you really must use SP magnum or SR primers in a small capacity handgun cartridge then use a starting load and just go with that. Attempting to "work up" to a previous velocity when SP primers were used can lead to higher pressures. That is what I would do and is what I suggest.

[megasupermagnum]

I would love to be corrected. The numbers I posted were what I calculated from what believe are stated by SAMMI. I'm not a statistics wiz, so it is very likely I am wrong. Here is what SAMMI says their definition of standard deviation is. They plainly state that MAP times .04 equals SD. Also stated, 4% variation is allowed.

Standard Deviation () - The Standard Deviation for each Maximum Average Pressure level is based
on a Coefficient of Variation of 4%. This 4% Coefficient of Variation is maintained throughout the
SAAMI pressure spectrum providing a realistic Standard Deviation for each pressure level. To
obtain the Standard Deviation for a particular MAP, multiply the MAP by 0.04 (i.e., 50,000 psi x
0.04 = 2,000 psi).


35,000 * .04 = 1400

I then took that, and used it to calculate that MEV number. Their definition is listed below.

Maximum Extreme Variation - The maximum allowable sample E.V. (Extreme Variation or Range)
is a statistic derived from the knowledge of the population Standard Deviation. Applying table
figures from the Relative Range Tables (Biometrika Tables for Statisticians) we calculate the
Maximum E.V. or Range as (population ) x 5.16 (table constant for sample of 10 at 99.0%
confidence level) i.e., 2,000 psi x 5.16 = 10,320 psi rounded down to 10,300 psi.

1400 * 5.16 = 7224

Unless I'm reading this wrong, according to SAMMI they are saying their recommendation for 9mm Luger has a MAP of 35,000 PSI, and allow a variance up to 7,224 PSI. I just noticed they state to round down to the hundred. Again, unless I'm reading this wrong, they say that as long as your pressure average is 35,000 PSI or lower, and you do not have any single readings over 42,200 PSI, you are within their recommendations, since SAMMI is voluntary.

I understand your concern, however, I just do not see any cause for alarm with using primers other than small pistol. I'm just some guy with no farther qualifications, so this is worth exactly what you paid for it. I have yet to see a pistol fail with a simple overload. It is always a squib (stuck bullet), double charge, or other extreme failure that would not have been prevented with a slightly reduced load.

[Larry Gibson]

megasupermagnum

It is likely you are wrong in several assumptions you make, as you surmise in your post.

Regards the Standard Deviation; your erroneous assumption is the SD as defined in the SAAMI definition you quoted is the same as the population SD mentioned in the definition of the Maximum Extreme Variation. They are two different SDs. One (the SD you quoted) is the maximum allowable deviation from the MAP. It is a simple +/- figure derived from the MAP X 0.04. Thus the acceptable +/- MAP of a 9mm P would fall between 33,600 to 36,400 psi resulting from any test of the population.

The SD used in the calculation of the MEV is derived from the calculated SD based on the actual measured psi's of a test. It is the mean deviation calculated from the average psi of the population (tested load). Unless you actually measure the psi of a sufficient sample of the population (10 shots is seemed an adequate sample) you will have neither the mean average of the psi along with the individual psi's from which to derive the SD used in the MEV formula. If you look at the psi SDs in the data you'll see none of them conform to the "MAP X 0.04" formula. They don't because they are a different SD for a different use.

The MEV also is not a +/- figure. The MEV is a psi "range" of which to compare the SD. Using the formula in the SAAMI definition of MEV will provide a psi "range" which the psi ES of the tested population should fall within. Note any of the psi SDs in the test data and use the MEV formula to compute the range of ES the SD should fall within. All fall well within the MEV which simply means they are fairly uniform but not necessarily "safe".

Your error is using the wrong SD to compute the MEV. Then misunderstanding the MEV to be a +/- psi figure to be added or subtracted from the MAP. It is not. Calculating the MEV based on the actual SD of the tested population merely gives you the range of which the measured psi ES should fall within. Useful information but not something to hang your hat on about using excessive pressure loads.

Using the SD from the definition quoted in the MEV formula has given you the erroneous psi figures from which you then compounded the error by misconstruing it as a +/- figure.

I am not telling anyone not to use them. I am just presenting factual test data. Many things we do on a daily basis are risky. We, individually, must decide how much risk we want to take. In my previous post I stated what I would do based on the data I have now if I had to. I don't. You are free to do as you want and to take whatever risk you please.

[megasupermagnum]

Thank you.

[SlamFire1]

Have you tested different lots of the same primer brands? Primers are a mix of components. there are allowable percentages in the mix, and the purity varies, along with the homogeneity. A Gun Club bud used to visit Government ammunition plants, he said primer cake is mixed by hand, and that the workers who made the most consistent primer cake received cash rewards. But, as he said, consistency is an "artifact". I got the idea winning was not random chance, but there was enough variability in the process, making the best was not guaranteed even if the worker did everything the same as his last winning lot.

It is quite possible, the next primer test, with different lots of primers, the results will be shuffled.

I am unaware of anything that the primer makers have put out about their process control, and their production standards. There is no particular reason to assume that slightly substandard lots are not shipped and sold, especially in times of panic, as what is going on right now.

[charlie b]

....It is quite possible, the next primer test, with different lots of primers, the results will be shuffled....


Or the results could be much worse than presented.

[ddixie884]

Great work as usual, Larry. Thanx for sharing the fruits of your labor............

[RJM52]

Great work as always and #13 answered the only question I had and that was what the effect be on a max load of a slower burning powder...

As we have discussed in the past, I have been running many .38 Supers since 1980... All of my high performance loads run with Small Rifle powders. Doesn't seem to have hurt anything and accuracy is always astounding...

Bob

[Hi-Speed]

Lyman’s latest 357 Magnum load data lists using CCI550 magnum primers with all its powders including Unique. Their 158 gr jacketed HP loads using Unique starts at 6.4 grs (CUP 18,900) and max 8.3 grs (CUP 38,300)…

Lyman also shows cast data using Bullseye up to 7.0 grs with 155 gr 358156GC SWC again using CCI550 primers.

Lyman also recommends the same CCI550 magnum primers for their 357 Mag loads using 2400.

Edited:

…removing my speculations and just going by what published load data recommends.

I have nothing but the best to say about Larry Gibson and all his fine work that he has done on behalf of our great forum. I always look forward to his very informative and analytical posts.

“Start Low, Work Up”

[David2011]

Larry, your posts are always worth reading. Thank you! The data regarding SR primers, pressures in particular, is noteworthy. I never challenged the published data other than to use a different brand of the recommended size primer. My loads are rarely near the top anyway, other than Ruger/Contender only loads for .45 Colt and .44 Mag. The folks that publish reloading data have far better equipment than my lowly Competition Electronics chronograph. Best to believe what they write.