I'm loading 38 special brass but I'm out of SP primers. Can I safely substitute SPM primers of which I have many? Thanks!

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S&W M60-15 Pro 3", M69 2.7"

This goes against typical "safe practices", but...

If you aren't already running a MAX load and you are using this ammo in a modern .38 Special or a .357 Magnum, you are unlikely to have any issues.

Even still, proper methods dictate that you re-work a load when you do this sort of change.

I've done it lots of times. Typically you will gain an average of 10 - 15 fps on velocity with no other noticeable effects.

Thanks but I'm not sure I understand. I'm loading per the HODGDON manual with 4.6 gr of CFE powder and 158 gr MEI Cast LSWC bullets. all according to the manual. Question is can I substitute Winchester SPM primers for Winchester SP primers?

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S&W M60-15 Pro 3", M69 2.7"

If the 4.6 grains is not near the maximum recommended load for 38spl case then it should be safe.

If it was me loading I'd lower the powder amount to about 4.3gr and load 10 test rounds

I've used magnum primers in target loads a great many times.

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NEVER GIVE UP YOUR GUN

Well, I don't have the Hodgdon manual or website in front of me, so I don't know what Hodgdon considers a MAX load, but I'll explain it more clearly.

If 4.6gr of CFE under a 158gr cast LSWC was a MAX load, you would not start there out of the blue. Instead, using proper (safe!) methods, you would start somewhere under that... most reduce a max load by 5%-10%, so you would start at maybe 4.1 grains of powder and you would advance that load looking for signs of high pressure. You would stop advancing the load when you:
1) get an accurate, "fast enough" load that you like
2) reach the published max charge
3) see signs of high pressure
(choose any that apply)

...and you would find your personal load in there. 4.6 grains is that load for you now.

At this point, -NO-, according to safe practices, you would not now simply take your chosen load (4.6gr) and stick a magnum primer in there.

Rather, you would prime cases with the magnum primer and start over again at 4.1gr and advance the load.

But I will re-iterate...
If this is NOT a crazy load, if you are using a modern .38 Special firearm and especially if you are using a .357 Magnum firearm, there is virtually no risk here.

Still, this would be outside the safe practices, especially for a new handloader.

Hope this helps.

Some say the Magnum primer is best with ball type powders....
Many state that you can use a touch less powder..........

I use them for all powders in my pistols and revolvers.
They can work well or be worse than a standard primer in a loading. You just need to test out loads to see what turns up.

Just follow the loading data in the manuals and you will be ok.

I have for over 40 years always used small rifle primers in all my .38 Special loads and never saw any difference in grouping or MV vs. regular SP primers. I'd expect to see exactly the same performance with SPM primers, although I have not used them. Not exactly the same, but I not long ago tested LR vs. LRM primers in a .270 with slow powder. Again, no difference seen in MV or grouping. If anything LR primers grouped a bit better than LRM.

Looking at the Hodgdon load data, I wouldn't adjust a thing. Just load them up and have fun. Your load is on the low end for that bullet anyways and I've found that CFE burns better on the higher end than the lower end of the loading data, with 9MM at least in my experience. The hotter primers might cut down the amount of carbon left on the cases. And if you are using Remington primers, the only difference between the 1 1/2 and 5 1/2 primers (SP and SPM respectively), is the thickness of the metal used to form the cup.

For reference, the Hodgdon data shows a powder charge range of 4.4 - 5.0 grains of CFE for that bullet.

The range per Hodgdon for your 158 bullet and CFE is 4.4 to 5.0 grains/ You state you are using 4.6 grains.

A SPM is not gonna make a whole lot of difference. They are not nuclear or Dilithum Crystals. Worst case is you may load a +P load. The mag primer i not going to equal .4 grains of powder energy.

Of course the correct answer is "C" start at the low end and work up.

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Still Running Against the Wind

I'm with Toolguy....I have used SPM in place of SP with no issues. When developing a load for new powder of new bullets i will even load test rounds containing both SP and SPM at the same powder load and test them against each other just to check if accuracy was affected which it doesn't. The only effect is a very small change in FPS and sometimes that doesn't even show up....Now if you want to talk about the effects of doing this with a magnum load then that's different story

Same here. This issue sometimes gets mentioned on other forums with almost 'paranoid' responses but I suspect most of that is due to lack of (or no real experience) reloading. I once read if one lives and shoots in a predominantly 'cold' environment then magnum primers should be used for ALL loads.

To detect any significant differences in grouping and average MV resulting from different primer types, one would have to fire a very large number of rounds of each to find out. A lot more than you might think.

I use Federal small match rifle primers in all 38 & 357 loads, Never had an issue

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ΜΟΛΩΝ ΛΑΒΕ

In this case you sure can use the magnum primer. That's not a particularly high pressure load and even if the magnum primer has higher brisance (they don't always) the extra pressure wouldn't be much. In a modern revolver it's just not a concern using book loads and substituting different primers where working pressures are only 20,000 psi or less.

Full on magnum handgun loads or hot rifle loads are a different matter.

You may see slightly higher velocity, along with slightly greater standard deviation. If you don't measure either of those things, I doubt you'll notice any difference whatsoever.

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Pisgah

Hey there was a time a couple years ago when one bought what one could find - I still have several hundred LPM primers (from a brick I got lucky to find) so I could load .45 ACP!

I accidentally used SPM in .380 loads one time and the load worked out so good and accurate I standardized on it.

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H Richard
SWCA1967 SWHF244

Then there's using SPM primers in 45ACP small pistol primer case loads...

Have yet to see any published load data distinguishing these cases: my personal experience is no real (or noticeable?) difference.

Cheers!

Yes you can. If course drop back the charge and work up as usual when you change components.

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Freedom is never free!!
SWCA #3437

Typically, your velocity will increase about 30 - 50 fps with Magnum Primers. No big deal if used in any gun in good condition, unless of course you are already shooting maximum loads.

Definitely need a sticky on this subject; "can I use _____ primers instead of _____ primers in my 29 SOT Special?" is way too common...

magnum primers in 38 special - Google Search