I have never used Small Pistol Magnum Primers in my 357 Magnum 158 grain .358" diameter L-SWC loads over 6.0 grains of Unique. Does anyone recommend the magnum primers for this load?

I would save the magnums for other loads. I doubt you would be over pressure with the magnums since the listed velocity is only 1kfps but obviously you should reduce and work back up when switching components. If that's all you have go for it. Otherwise it's a waste.

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The magnum primers are for hard(er) to ignite powders than Unique. The cups may also have slightly different specs to better withstand high pressures. In 50 odd years of reloading .38/.357 I've only used the magnum primers once, and that was recently, because the load data was developed using them AND, I'd bought 500 of them by mistake.

Unique works just fine with both magnum and non-magnum primers.

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FBINA 213th Session

Thanks for the replies. I'll stick with Small Pistol Primers.

Most handloading manuals specify magnum primers with all.357 loads due to the tall case and air space with light loads. My chronographing tests show improved consistency with magnum primers with all .357 loads, light to heavy so that’s all I use.

I use SPMP with 2400, SPP with Unique, never problems since 75.

You could use magnums in it, but there's no logical reason to support it outside availability.

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it just needs more voltage

If you get a pierced primer, ever, switch to magnum.

If using 2400 powder, a WSPM primer will require a reduction in 2400 powder.SAAMI PRIMERS | The High Road

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I have often read that the Magnum primers were for slower powders like H110 or 4227.

I have noticed myself that a magnum primer can clean up a dirty load (unburnt grains of powder) some as well.

Prescut

Alliant doesn't recommend magnum primers with Unique in the .357 Magnum. I'd rely on their expertise.

Small Rifle primers will work just as well. Pretty much identical to a SPM primer. I have used SR primers only in all of my .38 Special and .357 loads for many years, and even in several other calibers.

I have used Federal magnum SPP exclusively in every 9mm, 38, 357 that I’ve loaded for the last 5-6 years with Titegroup, Bullseye, Unique, Universal, CFE Pistol, 2400, H110 and Lil Gun. I have seen no noticeable difference except it does help some powders burn cleaner. I’ve checked loads as light as 2.7gr Bullseye to Max loads with 2400 with a chronograph and saw more difference from gun to gun than I did from Std to Magnum primers. No high pressure signs. Your results may vary but I’ll continue to use magnum since that’s all I have

Magnum primers are only needed for powders which are hard to ignite like W296/H110, HS-7, HS-6 and the like. They work better when lit by a magnum primer.

Unfortunately load manuals these days use SPP for .38 Special and other "standard" cartridges while they use SPM primers for anything that has a "magnum" name. I wrote Hodgdon and asked them why and they said they use and list a magnum primer for cartridges like the .357 Magnum because even if the powder doesn't need one because they are concerned some reloaders will not read the primer used and assume a magnum primer is required. That may raise the pressures making the max powder charge no longer within the max pressure limits.

If you have older manuals like the Speer 8 or 9 look at the data for the .38 Special using HS-6/W540 and you will see a magnum primer was used in the load development.

Unique and 2400 are very old powders developed before magnum primer were made. They seem to perform better with a standard primer over a magnum primer. The SD and ES numbers are lower with standard primers so that's what I would use, even with 2400 in the .357 Magnum.

I hope this helps a bit...

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SWCA #3437

The older genuine Alliant and Hercules manuals used Federal 200 primers with all loads and powders, even Bullseye and Red dot. The current published Alliant data isn’t the data originally developed by them.

I gave up on pistol pistol primers, standard or mag, for my full .357 "magnum" loads years ago and only use Federal 200 Small Rifle.

No. No need for mag primers with Unique.

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Grumpy Old Man With a Gun

That’s correct

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FBINA 213th Session

Magnum small pistol primers aren't just about explosive material quantity. The most important aspect is primer cup thickness. I would recommend loading .357 magnum loads with magnum primers for the thicker cup...primers are the main weakness of small-primer handgun cartridges because even the magnum versions have thin cups. In fact, if your hammer system can handle it I'd recommend working all loads up using small magnum RIFLE primers to get the super-thick cups that don't flatten out like velum at 36K psi.

Literally ALL reload manuals say to use small pistol magnum primers. I only use them and I've been successful with hot loads H110 Hornady XTP 125 and 158 grains projectiles.
You're free to use what you want, but I have a 100% success and still have all my fingers, I'll stick with that.

Most of the primers I have purchased in the past 2 years, have been magnum primers, because those were the ones not being purchased by others. 1K of large rifle magnum, and 1 k of small pistol magnum. Small pistol magnums can be easily made to work in small pistol or small rifle brass.

I've loaded 357/44 mag for years, NEVER bought a mag primer in my life. I use 2400 exclusively, but standard primers worked 100% with 110 and 296 as well.

Right now, you use whatever type of primers you can find. Not a good time to be choosy.

I'm happy to hear you have had no problems with W296/H110 with standard primers but when used with Magnum primers the powder burns more completely and the ES and SD numbers drop in most cases.

Slow hard to ignite powders like W296/H110, W540/HS-6, W571/HS-7 ( both HS-7 and W571 are now discontinued) and other powders like them shoot better when set off with magnum primers.

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SWCA #3437

Negative.

My Speer manual lists small pistol primers for most loads. They list magnum primers for loads using certain powders (W296, HS-6, HS-7, etc.)

edited to add: I was concerned about the age of my Speer manual (12th edition, 1995). Their online data still has magnum and standard primers based on powder.

additional edit: I removed mention of a different manual as there was no mention of Mag primers for any loads using small pistol primers leaving things ambiguous.

Don’t own a chronograph do you? If you did you would see how extremely poor your handloads with 110/296 and standard primers actually are.

Remington primers- https://www.ssusa.org/content/reming...istol-primers/


Indeed, Remington’s ballistics tables list the recommended primers for each caliber that Remington loads, handgun and rifle. The 1½ primers are listed for the 25 Auto, .32 S&W, .32 S&W Long, .32 Auto, .380 Auto, .38 S&W, .38 Short Colt and .38 Special. None of these cartridges exceed 25,000 psi peak chamber pressure limits. Surprisingly, the 1½ primer is also listed for the 9mm Luger, the 9mm +P and .38 Super. These latter calibers are not low pressure. The 9mm Luger has a SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) pressure limit of 35,000 psi, and the +P version’s limit is 38,500 psi. The .38 Super has a SAAMI pressure limit of 36,500 psi. These compare with the .357 Magnum and .40 S&W pressure limit of 35,000 psi, and the .357 SIG’s limit of 40,000 psi. If the 1½ primer is not appropriate for the .357 Magnum and .40 S&W, how can it be appropriate for the 9mm, 9mm +P and .38 Super, which have the same—or even higher pressure limits?

This has caused confusion among some reloaders, myself included. In fact, I was unaware of this warning when I first bought 1½ primers and used them in 9mm Luger loads. I thought the 1½ primers were “standard” primers, and the 5½ primers were “magnum” primers, since that is how they are listed in many primer charts.

In my 686 I have been loading sub 1000 fps target loads with True Blue and, due to availability, have been using small pistol, small pistol magnum, and small rifle primers without any problems. No signs of any pressure issues and if there is any affect on accuracy, it's too small for me to notice.

I have been using SRP in all of my handgun loads this year because of the paucity of SPP. I’ve had zero issues, firing in Glocks and my cheapie Beretta APX, due to the thicker cups. All of my reloads are mild pressure-wise so no concern with using small rifle primers. As others have stated, I am reasonably sure that SRP = SPM.

This is an epiphany I have had recently. I have heard the argument for the thicker primer for the higher pressures, but as you stated, 9mm and 40 both run pressures the same or higher than 357 mag, but I have never seen any load data call for mag primers in either, so that debunks that argument.

Only argument I have heard that does make sense is that some powders need a hotter flame to burn consistently. And that some ball powders such as H110 may burn fine at normal temps, but in cold weather environments, that is when you really start to have hang fires and the like and a mag primer will take care of that.

Other conclusion I have come to. Magnum in a cartridge title is used in a different context than Magnum in a primer name. 2 different uses of the term. In a cartridge, it was really just a marketing name to sell products. In the primer, it really means a hotter flame and also varies from manufacturer to manufacturer.

For example, a .270 Winchester runs higher pressures than a 7mm Rem Mag. And as you stated, the 9mm and 40 may run higher pressures than a 357 mag and 44 mag.

Rosewood

The powder and to some extent the amount of that powder determines when a magnum primer is used .
Ball powder and large charges of slow burning powder like 2400 and H110 can benifit from magnum primers .

Unique is a medium burning , easily ignited powder .
6.0 grains is not a large amount ... no magnum primer needed ... BUT ...
If all you have are magnum primers ... in this load you could use a magnum primer and get a few extra feet per second in velocity .
It will not create dangerous pressure in a 6.0 grs. Unique load ( a max. load like 7.0 grs would call for a reduction but 6.0 grs. is fine) ... you might even get a bit better accuracy in the 357. magnum case .
Load up a few and test them ... the primer shortage is causing a lot of folks to start using magnum primers because that's all they have left and/or all they can get !
Gary

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Lately I've found mag primers are more readily available & priced cheaper than std . Large rifle all I've seen are CCI 34's & Ginex .

Regardless of whether you are loading with Unique or other powders, use what primers you have or what you can find. Your gun, your components, and your shooting skill are different from those of others.

I've seen slightly better accuracy with a magnum primer, #2400 powder, and a 160 gr. SWC cast from an H&G #51 mould and fired in a 6" Python vs. the same with a standard primer. Hardly definitive proof of anything.

Try both primers (or as many varieties as you can find) and fire some ten-shot groups benchrested at 25 yards. A chronograph would be handy, but not necessary. If you use a chronograph, look at the velocity figures and check the target for group size; don't fixate on SD and ES numbers which are very secondary.

I’ve tried spm and srp in 800-950fps unique,win244, and aa5 loads in 357 brass, 158gr plated and jacketed rn and swc, they do burn cleaner than sp in my experience.

2400,h110, and 4227, I started at the minimum, I found the accuracy I was after with the charges lower down the spectrum vs what sp achieved, not every gun is the same obviously, but you get the idea. 2400 and 4227 were rancid filthy with regular sp’s, h110 wasn’t nearly as bad as those two.

Like I said above, the need for a magnum primer is powder driven, not by the word Magnum in the cartridge. IMO Unique and 2400 don't require a magnum primer. They are very old powders which were formulated well before magnum primers were ever thought of. Hard to ignite ball powder are the magnum primer candidates.

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SWCA #3437

I have been trying 6g Unique with both hard mix and reclaimed range lead 158g LSWC gas check, sized .357, (what I got), with both standard and Magnum primers, in 357 case. Accuracy is shotgun cylinder choke. In a 586 4" same bullet over 4.1g 231 in 38 spcl case with std primer is more near one hole at 10 yds.

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