IMR 4350 Primer requirements

1972RedNeck · May 13, 2024, 01:24 PM

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?

Paul B. · May 13, 2024, 03:55 PM

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.

**Unclenick** · May 13, 2024, 05:06 PM

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.

stagpanther · May 14, 2024, 06:54 AM

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.

jmr40 · May 14, 2024, 07:13 AM

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.

stagpanther · May 14, 2024, 09:42 AM

It's also fairly common for people to download big cartridges for "casual" low-recoil shooting--that adds to the equation IMO.

FITASC · May 14, 2024, 05:12 PM

Here's some showing in stock:
https://texashuntingequipment.com/pr...e-rifle-100box

May 13, 2024, 01:24 PM	#1
1972RedNeck Senior Member Join Date: December 8, 2015 Posts: 213	IMR 4350 Primer requirements 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?

May 13, 2024, 03:55 PM	#2
Paul B. Senior Member Join Date: March 28, 1999 Location: Tucson, AZ Posts: 3,807	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. __________________ COMPROMISE IS NOT AN OPTION!

May 13, 2024, 05:06 PM	#3
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,104	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. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

May 14, 2024, 06:54 AM	#4
stagpanther Senior Member Join Date: March 2, 2014 Posts: 11,921	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. __________________ "Everyone speaks gun."--Robert O'Neill *I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!* Last edited by stagpanther; May 14, 2024 at 09:40 AM.

May 14, 2024, 07:13 AM	#5
jmr40 Senior Member Join Date: June 15, 2008 Location: Georgia Posts: 10,825	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. __________________ "If you're still doing things the same way you were doing them 10 years ago, you're doing it wrong" Winston Churchill

May 14, 2024, 09:42 AM	#6
stagpanther Senior Member Join Date: March 2, 2014 Posts: 11,921	It's also fairly common for people to download big cartridges for "casual" low-recoil shooting--that adds to the equation IMO. __________________ "Everyone speaks gun."--Robert O'Neill *I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!*

May 14, 2024, 05:12 PM	#7
FITASC Senior Member Join Date: December 6, 2014 Posts: 6,464	Here's some showing in stock: https://texashuntingequipment.com/pr...e-rifle-100box __________________ "I believe that people have a right to decide their own destinies; people own themselves. I also believe that, in a democracy, government exists because (and only so long as) individual citizens give it a 'temporary license to exist'—in exchange for a promise that it will behave itself. In a democracy, you own the government—it doesn't own you."- Frank Zappa