Reloading .357 magnum using small pistol primers - range report

[CapeCodReloader]

Avid reader of posts on NES, and have learned alot. Now I would like to add to the reloading information stored here.

Today I reloaded some .357 Magnum, with the main goal of seeing what actually happens when you use small rifle primers vs small magnum pistol primers. (im out of small pistol magnum primers, but i have a good supply of small rifle primers)

And before the flurry of people warning against not following prescribed loading data in published manuals - I agree, for safety, one should follow verified published loads. But sometimes I have find answers myself. And I like to inform other reloaders with real data, not hypothesis.

so here goes - all rounds loaded with 158gr FMJ, 16.5 gr H110, virgin starline brass. I tested with Fed 200 small rifle/small pistol magnum primers as my control. I then tested Fed 205 SR, WSR, and CCI 41 (for 5.56mm). I shot from a TRR8 revolver with 5" barrel, and a Rossi R92 with 16" barrel. 5 shots of each load, one for velocity, a second for general accuracy. The test gave some very concrete results.

- First up, velocity -
Fed 200 Small pistol magnum/small rifle primers - the control
TRR8 -- Rossi
1050 fps SD 45 -- 1632 fps SD 16

Fed 205 small rifle primers
1042 fps SD 46 -- 1628 fps SD 31

WSR small rifle primers
1025 fps SD 55 -- 1605 fps SD 11

CCI 41(for 5.56mm)
1074 fps SD 65 -- 1655 fps SD 22

Looking at avg FPS and SD, no huge difference in performance using small rifle primers for 357 magnum reloading

Next Accuracy

TRR8 revolver, FED 200 load - accuracy was on par with my normal ability

Using any of the 3 small rifle primers - my groups were consistently 4-5x LARGER, and no real grouping, they were all over the place. It was ugly.

Rossi 16" R92, FED 200 load - accuracy was on par with my norm

Using any of the small rifle primers - my groups stayed the SAME SIZE as the FED 200, and very acceptable

In conclusion, can you safely substitute small rifle primers for small pistol magnum primers in 357, I say yes.

Should you? If loading for a revolver, NO, its not worth the crappy accuracy
for a rifle - yes - worked just fine

As to WHY accuracy suffered in the revolver vs rifle - well thats a whole other topic/rabbit hole to explore.

 

[SJan]

Results will vary greatly depending on the powder used. H110 and similar will need the magnum primer to properly and consistently burn all the powder. With a mild load of something like Titegroup, won't be much if any difference.

The powder has more time to burn in the longer rifle barrel, that's why your accuracy there was unaffected

 

[CapeCodReloader]

Results will vary greatly depending on the powder used. H110 and similar will need the magnum primer to properly and consistently burn all the powder. With a mild load of something like Titegroup, won't be much if any difference.

The powder has more time to burn in the longer rifle barrel, that's why your accuracy there was unaffected

I agree with results will vary with powder, but I only use H110/W296 for .357 magnum. As far as barrel length/incomplete powder burn, i would agree with that, IF the avg FPS and SD varied in the loads with 3 small rifle primers vs the 1 with a small pistol magnum primer. But the velocity and SD for the 4 primers were close with no definitive difference. Meaning, apx the same amount of powder was burned in order to achieve the same/consistent velocity.

 

[EddieCoyle]

The only problem I've found is that some guns light strike more with rifle primers vs pistol primers (especially with the CCI 41s).

 

[DW357]

The only problem I've found is that some guns light strike more with rifle primers vs pistol primers (especially with the CCI 41s).

This. If you have a tuned revolver with ligtened springs etc. there's a VERY good chance you'll get light strikes with SRP.

 

[DW357]

I'm not surprised at the velocities but kinda surprised at the accuracy changes.