Is there a standard rule for going from std rifle primers to magnums?

[smong2000]

I just read an article on loading for the 358 Win by J. Barsness where he switched from std rifle primers to large rifle primers and was able to reduce the powder charge while maintaining or increasing velocity.  I realize he is the expert but I have 4 different reloading manuals and have found no 'rules' for when you can use magnums and what reduction in powder to use if you do use them and none even list magnums for .358 Win loads.  My rifle has a very short throat and I'd like to seat my bullets deeper so this seems to be a potential way to do that IF it's safe.  His loads use TAC powder which I can't find locally so I'm stuck with 100%+ loads in most everything else to get any kind of velocity.
Can Magnum Primers be substituted for regulars without danger if the charge is reduced and if so what kind of reduction from starting loads?
Thanks   

[Graybeard]

Nope not really.

[Sweetwater]

GB +1

Yes, no, maybe, sometimes, and never are probably the only standard rules of handloading.

There are experts and there are experts. This forum is full of experts, with lots of experience; mostly not paid and published. I like J.B., but that doesn't mean I agree with everything he writes. Heck, I reread some of my posts and don't agree with myself!! LOL! All aside, Yes, as a general rule, you will reduce the powder charge to maintain velocity switching from standard to magnum primers IF AND ONLY IF you are willing to accept any digression of accuracy by going to the hotter primer. You will be starting over with a new set of test loads to find your sweet spot, as there is NO RULE for standard conversions.

Not sure what you have for manuals, but I just made a quick check of my Speer #12 because it was handy, and several loads for the 358Winchester are shown with magnum primers. Remember, theses are guides only. If you switch say from CCI standard primers to Remington standard primers, you have upset the labratory findings of "the book". So, a little judgement is in order. A check of several manuals only shows a few loads as being compressed, HOWEVER, they also show the loads as to be approaching max pressure areas, so I'm not sure as to what you are really trying to accomplish here. The 358W is a great cartridge, far better than it's given credit for being, BUT it is not a hotrod, and doesn't need to be. SO, to answer your first question, NO there are no rules, other than the rule of good judgement; nothing here is black and white. What works in one rifle may or may not work in another.

As a bonus; some of my manuals show a mag primer and some show a standard primer for the same powder and cartridge. However, they show very different powder charges for the same velocity. Velocity is a product of pressure, but also a product of how that pressure came to be. ie the pressure curve. There is no magic that is going to bring several hundred fps more velocity to the 358W with the powders that we have available today without taking pressures into the danger zone - next year, maybe.

Good luck and stay safe!

Regards,
Sweetwater

[roper]

Here a clip from Ramshot powders they make Tac rifle powder

"It's been my experience that I need to use a magnum primer with spherical powders. Do I need to use a magnum primer with Ramshot powders?
A: While this may have been true with spherical powders in the past, Ramshot powders employ a new technology of coatings which increase ease of ignition, cleanliness and in most cases decrease temperature sensitivity. You also have to take into account your firearm's accuracy which may or may not perform better with magnum versus non-magnum primers."


I think Speer may be one of the last manuals # 14 that list mag primers with Spherical podwers.  As much as I like to read shooting articles I don't put much into wanting to try their loading data.

[wncchester]

Semi, sorta.  Mostly, use magnum primers for (real) magnum cartridges,  standard for standard.  

Sometimes ball powders in standard cases will see some benefit with magnum caps.

[84Jim]

Here's some food for thought.  I had seen a similar study some time back, but found this one easily so I'm posting it.  Of course the results depend on the accuracy of the testing machine, which looks to be home made.

If you can believe the test, the conclusion would be that primer strength differs by company, and probably has potential to vary significantly by lot.  Some of the ones with a high SD apparently have a pretty big variation within the same lot.  The study I had previously saw had several standard LR primers ranked above Rem 9 1/2 M.

http://www.castingstuff.com/primer_testing_reference.htm

[charles p]

I load ball powders in 7mm-08 and 308 with standard primers and get excellent results.  Lots of sources say magnum with ball powders.  Go fishing!

[wncchester]

Yeah Charley, if ANYTHING was a certainty guess we would all be doing things just one way!

[BBF]

the manuals used to say Magnum for ball powders. Not all magnum primers are the same and that goes for standards as well.Unless things have changed, Federal 215 are the most brutal ones

I'm partial to magnum primers for standard or magnum cases that use any powders that have a slower burning rate then the 4350 types.

[buck460XVR]

My rule is, if the manual says use a magnum primer, I use a magnum primer. Regardless of what the internet "experts" claim. I use standard primers with many true magnum loads, because again, that's what the published manuals say to use for that type of powder. Many claim it has to do with the amount of powder used....it does not. It depends on how hard the type of powder you are using is to ignite.