Rifle vs pistol primers - why?

SPM and SRP can be used in SPP applications, just work up the loads and don't load to max published data.
LPM can be used in LPP applications. Same precaution.
Don't use SPP or SPM in rifle applications. Small pistol primers are not designed to handle 55kpsi (although I've never tried disproving it).
Don't interchage LRP and LPP. The heights are different.

If I'm in need of SPP's and if only SPM or SRP's are available, I don't hesitate buying and using them. My chrony data shows no difference but I never load pistol rounds to max anyway.

It varies by manufacturer, but small rifle primers often have harder cups than the pistol primers. If you're trying to run reduced-power mainsprings/hammer springs/striker springs (in pursuit of a lighter pull), you'll have reliability problems with some rifle primers before some pistol.

It's not true that "it's binary, you're either igniting the charge or you aren't." Different brissance levels generate different ignition patterns in the powder, and can change peak pressures.

All that said, lots of guys shooting open guns in 9mm major or 38 super +P+ run rifle primers to prevent the pistol ones from shredding at rifle-like pressures and fouling up the gun.

rsrocket1 said:

SPM and SRP can be used in SPP applications, just work up the loads and don't load to max published data.
LPM can be used in LPP applications. Same precaution.
Don't use SPP or SPM in rifle applications. Small pistol primers are not designed to handle 55kpsi (although I've never tried disproving it).
Don't interchage LRP and LPP. The heights are different.

If I'm in need of SPP's and if only SPM or SRP's are available, I don't hesitate buying and using them. My chrony data shows no difference but I never load pistol rounds to max anyway.

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Data for the .327 Federal Magnum has loads using small pistol primers at very high pressures. Other data shows small rifle primers.

I know the .327 is an oddball because of the high pressures it operates at 45K psi. That's quite a bit higher than most pistol cartridges.

Texas10mm said:

Data for the .327 Federal Magnum has loads using small pistol primers at very high pressures. Other data shows small rifle primers.

I know the .327 is an oddball because of the high pressures it operates at 45K psi. That's quite a bit higher than most pistol cartridges.

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A couple other oddballs are 460 and 500 S&W, where they use large rifle magnum primers. 460 is rated for 65k psi, same as magnum rifles.

Besides the different "brissance" mentioned by @ATLDave , the cups will be different thickness and/or hardness for the different applications.

Yep. It's hard to generalize across all the different brands, but there are several characteristics that are commonly different. Do those differences matter? It depends on the application. As always, the differences are more likely to matter in marginal cases... the gun that hit just barely hard enough to light pistol primers, the powder charge with very low density that flashes over, the low-charge load that allows the bullet to move (perhaps into the rifling) before the powder ignites with a too-strong primer, the max load that becomes over-max with a too-strong primer, etc. But in many applications, it wouldn't matter. No clear "yes or no" answer to the question.

The real eye opener for me was when I tried small primer 45acp brass and Trailboss powder. As a result of that experiment, I now use small magnum primers in 45acp, as they are much closer to the regular large primers. I don't care what anyone says, there is a difference between large and small primers in 45acp! Most powders, though, won't show much difference.

The main difference is pressure rating and primer compound used. In general pistol primers run 35k, where rifle is 55k. There are quite a few calibers that cross the bridge. Like 458 SOSOM use LPM primers and slow magnum powders.

There is a difference in velocity on a 45acp between SP & LP. I measure an average of 20-25fps difference.

I inadvertently loaded some 40 S&W with SRP. I've read, and have been told that they should be fine. I have not shot them yet. I will definitely want to chrony them, just to see if there might be any difference.

Some pistols (e.g. some striker fired guns) won't reliably set off rifle primers, especially the magnum rifle primers which have thicker cups than standard primers.

Information on primers:

http://www.shootingtimes.com/editorial/small-vs-large-pistol-primers-45-acp/99626

https://www.starlinebrass.com/articles/Small-Pistol-Primers-vs-Large-Pistol-Primers/

http://www.shootingtimes.com/editorial/ammunition_st_mamotaip_200909/100079

https://www.gunsamerica.com/digest/reloading-primers/

https://www.ssusa.org/articles/2018/5/15/remington-1-pistol-primers/

Blue68f100 said:

There is a difference in velocity on a 45acp between SP & LP. I measure an average of 20-25fps difference.

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For most powders, I've seen about 30-35fps, and unless I had a chrono I would hardly notice the difference. But when I tried Trailboss, I saw a huge difference.

Trailboss 5.5gn, RMR 200 RN plated @ 1.245". Witness 4.5" barrel.
Win large primer - 744fps
Win small primer - 575fps
Rem 6.5 primer - 682fps.

The only other powder I saw a significant difference was PB (now discontinued)
PB powder, 5.4gn, Xtreme 200 SWC plated @1.225"
WLP - 655fps
WSP - 554fps
WSPM - 639fps
CCI 500 - 587fps

PB powder 4.8gn, Xtreme 230 RN plated @ 1.225"
WLP - 614fps
WSP - 534fps
WSPM - 585fps

I chose low to mid range charges for purposes of the experiment.

CMV said:

What would happen if you were using SRM in your 9mm?

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There are people who do this. You would want to workup the load with the SRMs since pressures are different from the published data.

CMV said:

Same for large rifle in a .45ACP - still gonna go boom right?

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Large rifle primers are taller than large pistol primers. So that would mean high primers when fully seated in the pocket. Would not recommend.

CMV said:

Isn't it binary - you're either igniting the powder charge or you aren't?

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Nope. You are not accounting for the additional pressure that the "hotter" primer produces or the differing primer cup thicknesses. In the Obama years, all I could get were SPM's. I worked up the load for the new primer which was a lower charge weight than my workup for SPP's. Everything was good until I tried it in my striker fired pistol. At least 1/10 would not ignite. Cool for tap, rack, and go practice the first mag. Very annoying after that. They weren't duds either and would fire in my DA/SA no problem.

We are just trying to save some heartache from people who have been there.

Stick with what your manuals tell. The loads listed were developed and pressure tested with the primer listed.

CMV said:

Dumb question and I have no intent of mixing them around, but what's the difference? I'm using 5 different primers - small pistol for everything except small pistol magnum for .357MAG & large pistol for .45ACP. Then small rifle magnum for .223 & 300BLK, large rifle for 308WIN.

Got wondering about it esp with .357MAG vs 300BLK. Same powder, roughly same charges per bullet weight, both small primers, but I need to use a small pistol or small pistol magnum for the 357, but need to use a small rifle to set off just about same thing in the 300BLK.

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Good question and I HAVE used "unapproved" primers in a variety of loads in efforts to get maximal accuracy. A case in point is the 357 Herrett loaded with a stick powder, IMR 4227. After a fair amount of testing the primer that gave the best results were CCI 250 primers; i.e., large rifle magnum primers. The dictum "just go by the manual" is good for the new reloader but hardly ANYONE does that. How often does one use the same brand of brass, the same powder, the same brand of primer and the same bullet in a load? That would be hardly ever and even if done it would NEVER be exactly the same in results because the pressure barrel they were tested will not be exactly the same in chamber, throat, barrel, etc., in your gun. As a reloader you ALWAYS have to work up your own load using common sense and evaluating for pressure signs so it doesn't matter if you use regular versus magnum primers as long as the load is worked up that way.

CMV said:

are there so many? What would happen if you were using SRM in your 9mm? Wouldn't the powder still ignite? Same for large rifle in a .45ACP - still gonna go boom right? Are you somehow going to "overignite" a pistol charge using a rifle primer instead?

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You're not going to "overignite" the pistol charge but the primer itself contributes some explosive energy that can make a difference. When trying large rifle magnum primers in some 44 Remington Magnum loads, I had to reduce loads by 1 or 2 grains. Unless you're on the bleeding edge of high pressure in a case the size of a 308 Winchester, you can exchange large rifle and large rifle magnum primers with impunity.

And regarding 460 and 500 S&W loads; some manuals use large rifle and others use large rifle magnum primers. I've always used large rifle primers.

Rifle primers may be harder than some pistol primers and some, not all, pistols might not touch them off. The fact that pistol primers are a tiny bit shorter than rifle primers can be ignored. I've loaded for 454 Casual, 460 S&W and 500 S&W guns which are all high pressure cartridges (50,000 to 65,000 psi). At lease one of those, I think it was the 500 S&W, initially had cases meant to take pistol primers so the pressure a firearm generates doesn't have much to do with which primer is used.

Toprudder said:

For most powders, I've seen about 30-35fps, and unless I had a chrono I would hardly notice the difference. But when I tried Trailboss, I saw a huge difference.

Trailboss 5.5gn, RMR 200 RN plated @ 1.245". Witness 4.5" barrel.
Win large primer - 744fps
Win small primer - 575fps
Rem 6.5 primer - 682fps.

The only other powder I saw a significant difference was PB (now discontinued)
PB powder, 5.4gn, Xtreme 200 SWC plated @1.225"
WLP - 655fps
WSP - 554fps
WSPM - 639fps
CCI 500 - 587fps

PB powder 4.8gn, Xtreme 230 RN plated @ 1.225"
WLP - 614fps
WSP - 534fps
WSPM - 585fps

I chose low to mid range charges for purposes of the experiment.

Click to expand...

You do realize there is an additional variable there, the WLP primers are rated for magnum use which is adding to the difference.

ArchAngelCD said:

You do realize there is an additional variable there, the WLP primers are rated for magnum use which is adding to the difference.

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Yes, and that is something I’d like to go back and try.

Once, during one of the many panics and the ensuing Primer Scare, I tested CCI small rifle primers instead of CCI small pistol magnums in my usual 357 Magnum loads.

Using my Performance Center 627, I found a clear degradation in accuracy, and unreliable primer activation.

You can safely use a small rifle primer in any small pistol application. They are exactly the same size. They gun isnt going to blow up due to it. I have done this with 45 (small primer cases) and 9mm. The only issue you might see is due to the thicker cup, some pistols might have issues setting the thicker cupped rifle primer off. However, my S&Ws do not. I have shot these loads from Glocks, Sigs and Springfields with no issues either. I think people that see problems are those that tinker with the springs in their pistols.

That being said, DO NOT SWAP large rifle into a large pistol case. The height of the rifle primer is higher, and will not seat below flush in the pistol case.

Cougar mentioned it above; different size larg pistol vs farge rifle primers. Thr difference is large rifle primers are .008" taller than large pistol primers.

I have been reloading for quite a while and started way pre-web. I experimented with small pistol vs small rifle, magnum vs standard, but never large rifle vs large pistol (LP would have prolly worked in LR applications, but never tried that). In all my reloading I can't remember where cup hardness has been much of an issue. My Garand or SKS have never had any slam fires and all my handguns have gone bang (once I learned to properly seat primers in '69) with the exception of one gun. I have an FMK 9mm striker fired 9mm that didn't like Winchester primers.The gun fired all other primers 100%, mostly CCI and Wolf, and the Winchester primed handloads worked in 2 other 9mm pistols. After research and experimentation I ran across an old magazine article mentioning "sensitizing" primers. My next Winchester primed loads got an extra "Ummph" when seating; all the way to the bottom then a good amount more pressure applied to the primer. These "preloaded" primers worked! 100%. Now when I use Winchester small pistol primers, for any cartridge, I preload them...