Magnum Primers Question

[USMCbrat]

A buddy of mine bought a brick of what he thought was Large Pistol primers and then realized they were magnum primers. I took them off his hands as I have wanted to try them in 44 Mag loads to see the difference with regular LPPs.

I have been working up loads with 240 grain LRNFP using Unique, H110, IMR4227 and 2400….all with standard LPP of either CCI or Winchester. All these loads were over 1200 f/s average muzzle velocity.

So my question is….when are Magnum primers optimal? Is it relative to the brand of powder, the amount of powder (volume in the case), the target velocities or something else?

 

[FrankD45]

As a general rule when substituting magnum primers for max loads that were developed with regular, you should step back perhaps 10%. That said, you mentioned using Winchester large pistol primers. I believe they are magnum rated so you should be ok substituting the magnum primers there. Again, if the loads are near maximum it is always smart to reduce the loads a bit when you change components.

I hope that helps,

Frank

 

[rundownfid]

You ask a number of very good questions. I hope someone more knowledgeable speaks up, but in the meantime I will pipe in with information, perhaps close to accurate.

The magnum primers are "hotter", so they tend to ignite the powder quicker. This can spike pressures so as FrankD45 mentions you should reduce the charge and work up.

Also, some powders are simply harder to ignite and work best with magnum primers.

Also, as you hinted there can be problems igniting very large powder charges, but I believe this is mostly in Magnum rifle sized charges, perhaps 65+ grains??

Cold can even make it more difficult to ignite the powder charge consistently, so magnum primers can make borderline loads more consistent across a broader range of temperatures.

Rereading this I sense I have used too many generalities. One more, it isn't that regular primers won't ignite the powder, but that when necessary, magnum primers give quicker, more uniform ignition.

 

[MTAustin]

I can't give you the science behind it, but I know Handloader magazine's very knowledgable Brian Pearce has written many times that magnum pistol primers should be avoided when using 2400, as it creates excess pressure. On the other hand, he recommends magnum primers when using H-110 or W296.

 

[USMCbrat]

So then all this begs the question ....What do the factory loads use? (as a point of comparison)

 

[TwoPoundPull]

Someone please step in and correct me if I'm wrong, but I believe Magnum primers may not necessarily be much hotter than a standard primer, they burn slightly longer than standard...

 

[jrplourde]

I think the long and the short is if the manual calls for mag primers for a given powder then use it; otherwise do not. Some powders are harder to ignite so need they need the extra flame and pressure but most do not.

Bob

 

[czakjm]

Originally posted by TwoPoundPull:
Someone please step in and correct me if I'm wrong, but I believe Magnum primers may not necessarily be much hotter than a standard primer, they burn slightly longer than standard...

You got that right! Back in the the early 90's when Clinton's anti-gun proposals caused panic buying, the only pistol primers I could find were all CCI magnum. I used them for reloading every handgun caliber I had, 380, 9mm, 38 Special, 45ACP, 45 Colt along with the 357/41/44Mags. Didn't matter what powder, all fired normally without any problems using published load data. Sure, mag primers kick up the working pressure, but I think the increase is marginal.

 

[Wickahoney]

The difference between standard and magmum primers is in the brisceance (heat generated by the explosive effect over time) this is a measure of BTUs over time. Magnums burn hotter for a longer duration.

As a general rules use magnums to ignite large volumes of slow powder. There are also some powders known to be harder to ignite.

The 7 1/2 Remington primer is a small rifle magnum that was developed specifically to ignite the powder type and volume used in the factory 17 Remington loadings.

While some powders are temperature sensative not all are. If you are going to load hunting loads for fall/winter hunting try to find the
powders that are listed as temperature stable.

Much of it is published data. In other cases or if in question simply comtact the manufacture and ask them. Both Hogdon and Accurate publish/published a small manual listing their stable powders. The Hogdon powders are listed as being "EXTREME". That is usable through a wide range of ambient air temperature without changing the pressure of the fired load.

Guys with a lot more time, knowledge and equipment work this stuff up for the reloading manuals so I usually follow their recomendations.

As mentioned if you switch from standards to magnums, back off at least 10% as the magnums burn hotter and generate higher pressures.

RWT