Does anyone have any thoughts they would be willing to share on what the results would be of substituting small magnum pistol primers for standard small pistol primers? For instance a load like a .38 Special target load, say 2.7 grains of Bullseye under a 148 grain lead bullet or a 9mm load of 4.2 grains of Bullseye under a 124 grain lead bullet.

Hi Slinkster,
This is not the end all opinion about this but for the loads you mention I doubt you will see much difference.
A warning though. The 9mm can be very pressure sensitive due to OAL and a different or hotter primer could make a difference in a near max pressure load.
The load you mention for the 9mm is one I am using now with Win. mag primers.
Back in the earlys days of .38 super "major" in IPSC/USPSA I used small rifle primers and for some reason ended up with a lot of them. I have used them in pistol loads of all kinds with out problems.
The only place I have found that a person should watch is when approaching max loads.
In all honesty I have not found that to be a problem but that does not mean you should approach max data with out caution.
Good luck and be careful
Mike

I gotta agree with mstuhr. If your loads are not max and show no signs of excess pressure in your guns, I doubt if there will be much of a difference. I always seek out at least 2 or more sources when developing loads. In many instances one load book calls for a magnum primer while another manual will have the same load(i.e. bullet/powder/case) and call for only a standard primer. I have also shot loads that were identical except for the primers and found no "seat of the pants" measurable difference in them as far as recoil and accuracy.

So long as your loads are not maximum, and the COL is not less than specified by the data publisher you likely will see no difference. The Magnum primers MAY give 15-30 fps more velocity, and may actually give slightly lower, and if you are chronographing your loads you will probably see a wider ES and higher SD with the magnum primer. Functionally you will never know the difference.

The magnum primers should not present any problems with the loads you suggest, but they do not offer any advantages either.

The only reason to use a Magnum primer is to reliable ignite hard to ignite powders. (like W296/H110) In some cases you will get poor results when using a Magnum primer instead of a standard primer. (like some loads using 2400) In most cases it's best to follow the components used when the data you're using was tested.