Magnum small pistol primers

[Tonup]

I hope someone here can help. I'm reloading for a 357 lever action using 158gr HP jacketed bullets over N110. The load calls for Magnum small pistol primers however, these seem to be pure unobtanium in the north of Scotland.
Looking at the CCI data, small rifle primers appear to be the same spec as Magnum small pistol primers.
Anyone know if that is the case?
It's either that or try standard small pistol primers.
I'd appreciate any advice!
Thanks

 

[Zeb]

I have a 38Sp/357mag long barrel revolver and a 357 lever gun for target shooting.
I bought a lot of CCI small rifle primers for my 6.5 creedmoor but found that I got some cratering at high loads. I switched to Small Rifle Magnum which solved the problem.
I read that CCI Small Pistol Primers and CCI Small Rifle Primers are similar. As I have a lot of redundant small rifle primers I tested them in my 357 revolver and found them to be interchangable. For this I used 38 Special loads knowing that I had a huge margin of pressure as it is proofed for 357 Mag. I found the Small Rifle and Small Pistol Primers to be interchangable.
I tried some CCI Small Pistol Magnum in the revolver and found about 50 f/s increase in MV, but a wider spread of MV and poor grouping. Out of curiosity I tried Small Rifle Magnum primers in revolver loads but of the 5 loaded 2 fired and 3 missfired. The cup thickness of Rifle Magnum is 5 thou thicker than the standard rifle primers which is why they work well in the 6.5 creedmoor. The firing pin spring in the lever gun is stronger and the Small Rifle Magnum primers work well. I do not know if this applies to brands other than CCI. I usually use 357 cases for all loads but if going down to 38 Special loads, keep in mind that the 357 cases are longer. The MV could drop too low if you use the minimum 38 Special loading. Whatever you try, work up, or down from a medium load.
In summary I don't know if Magnum Pistol Primers are the same as standard Small Rifle. I suspect that the Small Rifle Primers will give a lower MV, but I am sure both will work well as long as you do a safe work up.

 

[Laurie]

Viht's online 357 data now specify SPMs for the 357 Magnum, but its last printed reloading manual (No.2 published 1995) specified Winchester WSR primers. I queried that at the time wondering if it was a misprint, but was informed that no, that was correct. Comparing N110 charges for the 158gn Speer JHP which is the bullet listed then and now, charges have risen over the 30 years. In the 1995 manual start was 13.7gn / max: 15.1gn for 33,300 psi. Today, it's 15.1gn start; max: 15.9gn, pressure no longer provided. {Edit: looking at the general introduction blurb to the cartridge in the 1995 publication, it says Primer: Small Pistol or Small Rifle', but actually uses the WSR rifle primer in the loads tables.]

SR primers will fit pistol case primer pockets but have a thicker cup according to research that James Calhoun published on this years ago, the thinner rifle models at 20 thou' vs 17 for the pistol type. They may be harder too so the combination might produce unreliable ignition with hangfires and misfires from light strikes with revolver firing mechanisms. Chemically, SPMs aren't necessarily the same as standard SRs either as they may use different mixes in the explosive pellet to suit the likely powders and charge weights in their respective cartridge types. So, if you want to try SR primers use the thinner cup / structurally weaker models (CCI-400; Remington 6 1/2; Winchester WSR; standard Russian SR which are the old PMC copper colour Small Rifle or the more recent Murom 'Competition' Small Rifle, both works code KVB-223). Magnum and match SR models use thicker/harder cups and therefore best avoided.

I suspect you wouldn't have any problems especially with N110, but as always drop charges and work up again, and desist immediately if you suffer a hang or misfire. Here's what Sierra says on the Issue:

Primer Substitutions - Sierra Bullets.

which doesn't help you much as it says you're out on a limb very much on your own unless you can find listed pressure barrel data for such a switch, which I'm pretty certain you won't.

 

[Laurie]

When I was putting the aforementioned Viht printed manual back on its shelf, I noticed the even older Lapua Shooting and Reloading Manual No. 2 (published 2000) sitting there, so thought I'd have a look to see what it recommended. (Separate companies back then even though they worked together closely.) In the cartridge information and introduction section, it shows primer the type as Small Rifle - no 'or anything else'.

In the cartridge description it says:

"As powder space is long and narrow, a reliable and powerful primer is required. Especially with slow burning powders such as N110, small rifle primers are recommended."

So, the Finns agreed on SR priming back then with this powder, and again you have pressure tested data. For Lapua's two 158gn jacketed bullets of that era, the EG410 SJHP (semi-jacketed) and F463 FMJ, minimum N110 is listed at 13.4gn and maximum as 15.3gn with a recommendation not to use charges less than the minimum shown. Neither pressures nor primer make and model are shown. (Viht made primers back in the 1980s/90s including a very thin/weak cup SR model its No.22. With Lapua using mainly Viht propellants in its data, it could well have been this one. I tried it in a tightly breached match rifle a few years ago in 308 Win SRP 'Palma' brass and it was hopelessly 'soft', so much so that I had to stop shooting the rounds primed with it and pull them.)

 

[Zeb]

A few months ago I bought a stupidly expensive calliper so decided to re-visit my primer measurements including cup and total depth. I have no CCI SPP, but have some Federal SPP. The cups of SRM are 0.0059” longer than the SRP with Federal having a slightly shorter cup. The more important measure is overall depth where all of the primers are within 0.0032”. Surprisingly the longest are SPM and SRP, The shortest are Federal SPP and CCI SRM.

I use Starline 357 brass. The depth of the pockets is slightly variable. As with most brass the head is not completely flat. My revolver has a competition trigger with a light spring but is reliable with SRP.

Laurie’s link to Sierra does make a very important point. Do not use pistol primers in anything other than a pistol round as even the pistol magnum primers are soft.
I also find that SRP is far to soft to use in 308 Palma.

These are batch specific measurements so other batches and brands could be different.