IMR 4350 Primer requirements

1972RedNeck

New member
I use IMR 4350 in all my "magnum" rifles. 7mm Rem, 300 Win, and 375 Weatherby

Normally I just use Large Rifle Magnum primers as that is what is recomended and they work great. But I am down to my last 1000 LRM primers and haven't been able to source any more.

I have been able to buy Large Rifle primers though.

I use LR primers in my '06 with IMR 4350 with great results. Will Large Rifle primers give me consistent ignition in my "magnums" with IMR 4350 or could I run into problems, especially with my 375?
 
I've use Winchester and CCI standard rifle primer in my .300 Win. Mag. with the long gone Winchester WMR powder. Velocity is close to 2900 FPS from a 26" barrel with most loads MOA or smaller. I never did get around to trying magnum primers so no idea it groups and velocity might be improved. I'll just I had no problems using the standard primers.
Paul B.
 
1972RedNeck,

Magnum primers make a larger volume of gas than standard primers. This is to provide adequate start pressure in the larger volume cases that magnum cartridges have. This is especially important with spherical propellants, whose burn rate is controlled by deterrents that have a high concentration at the grain surface and then diminish exponentially so the burn into the grain makes gas progressively faster as the grain burns down, despite the surface area of the grain shrinking as it burns. It is quite a feat, but it means the surface concentration of deterrents in the grains has to be high, making them harder to ignite. This situation is improved by the magnum primer's higher start pressure, and the aluminum in most magnum primers makes hot sparks that can burn through the outer deterrent layers.

Stick powders are not as hard to light, so magnum primers have less benefit with them. Also, whether you use magnum or standard primers, either powder type will still ignite and go boom. The issue is that with a bigger space to pressurize, the harder-to-ignite powders may not pressurize and burn as consistently without magnum primers. This results in bigger velocity SD and larger groups, especially at longer ranges. Note that folks using larger medium power cartridges, like 30-06, can also see a benefit to using magnum primers when their load density is low. This is because the empty space in a low load density cartridge needs more gas to pressurize, too. A lot of folks shooting "Garand loads" in 30-06 have found better consistency and accuracy with magnum primers because a lot of those loads only achieve about 80% loading density, leaving a lot of empty space in addition to the space between the grains that is already there.

So, go ahead and run the standard primers. I had a situation once with poor ignition of a poor case-fill load of a spherical powder in .308 when I used standard primers, but it was significantly improved either when I used magnum primers or when I deburred the flash holes in the cases. Your 4350 shouldn't be as difficult as a spherical powder without a magnum primer, but if your cases have burrs, I would go ahead and deburr them so you have the maximum uninterfered-with ignition spark from the standard primer.
 
I'm in the same boat--I have many magnum chamberings in rifles and am down to my last box of LRM primers as well. I personally have agonized over this very issue and have decided it's just not worth the risk for me personally in my higher-capacity magnums. Probably little risk of catastrophic failure--but a non-uniform ignition potentially resulting in misfires and erratic distribution of pressure spikes is a distinct possibility the way I see it.
 
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Winchester Large Rifle primers are reportedly closer in performance to magnum primers than other brands.

I had a 300 WSM that I loaded for a few years ago. I used WLR primers in it when I ran out of magnum primers simply because that is what I had. It made zero difference. Of course, the WSM's are borderline on needing magnum primers anyway.
 
It's also fairly common for people to download big cartridges for "casual" low-recoil shooting--that adds to the equation IMO.
 
One thing to think about. At least with CCI magnum primers have stronger/harder cups than the standard primers. They generally will show signs of pressure sooner.
 
30-06 has a case capacity of 68gr. 375 H&H has a case capacity of 96gr. The '06 has proven performance over generations with medium burn powders. I use RL-15 with 165s.
 
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