Why Magnum primers?

[HammerMTB]

Here is what prompts my question: I reload for my 5.56 and it takes an almost identical charge of powder. Those seem to work fine, tho I will admit that I have never tried Mag primers for the 5.56. The general theme seems to be Mag primers for the 6.5 Grendel. Has anyone questioned this or done any real-world tests to demonstrate the need? It's not that I can't get the Mag primers if I need, it's more that reason alone doesn't dictate their need, and it's one more different component to stock. I have bricks of Small Rifle standard primers now. I'd prefer to use those unless there's a good reason not to....
Oh, in case the question needs to be answered, I use H4895 mostly, but had some IMR4895, and might use some BL-C2 as well.

[rasp65]

Magnum primers have thicker cups and stand up to pressure better.

[longdayjake]

Well, the harder cups can take more pressure, but I don't know if that is an issue with the grendel. 5.56 is loaded to pretty high pressures. It is probably just the product of some very experienced reloaders that don't use anything but magnum primers because they believe that they improve the standard deviation. Thats just a guess. I don't use magnum primers.

[pappy42]

Folks, the tougher primer cups help prevent slam fires in AR type rifles. I don't think that it is a pressure or ignition issue.

[bwaites]

Pappy is correct, but we should extend that to include piercing of primers in AR's as well.

However, Bill Alexander tried multiple primers when he was experimenting, and found the CCI450's gave him the most consistent ignition, least chance of slam fire, etc. Thus most of his loads were developed with them. He has said that Wolf small rifle magnum primers are very good as well, and some loads have been developed with those as well.

Lots of people have been happy using both bench rest and standard primers without issues, but the thicker cup of magnum primers allows some safety margin against piercing and slam fires as noted.

[HammerMTB]

Thanks to all who replied. They all make sense. I will be using std primers for now. I have never had a slam-fire, and while I don't say it couldn't happen, the likelihood is remote, and I will deal with it if it comes up.
Since 400 of my ~500 cases are currently LR size, I may not even concern myself with a test until my sample size is bigger.
Again, thanks to all!

[skyfish]

Just one question to add. When comparing CCI SRP(400) to CCI SRMP(450), is the flash(burn) more or hotter or is the primer cup just harder?

[Rapidrob]

Magnum primers are hotter. Greater initial pressure is generated as the primer fires. The initial rule of thumb is to reduce your powder load by one full grain. For those of you who are using a max loading now, you can get into trouble just by changing to a magnum primer. Please be careful I'd hate to see anyone get hurt or ruin a good rifle.

[GregP42]

Magnum primers?

I have noticed in all the reloading data I have found that everyone is using magnum primers, is there a reason for this? Should I be using magnum primers in my brass that uses large rifle primers too?

Thanks,
Greg

[bwaites]

Search is your friend!

http://www.65grendel.com/forum/showthread.php?126-Why-Magnum-primers&highlight=magnum+primers

[GregP42]

Thanks, I looked but didn't see that when I searched.

[davidj]

Magnum primers are hotter. Greater initial pressure is generated as the primer fires. The initial rule of thumb is to reduce your powder load by one full grain. For those of you who are using a max loading now, you can get into trouble just by changing to a magnum primer. Please be careful I'd hate to see anyone get hurt or ruin a good rifle.

Not to mention a good face.
One should also be careful using WSR primers. There is a higher incidence of slam fires with the new WSR primers. Apparently the new copper tinted primers are a lot softer than the older chrome colored ones.

[bwaites]

Merged the two threads!

[PrecisionFirearms]

We recommend using CCI M41 Primers in all loads for the 5.56 but not for the 223. Using a Magnum Primer with load data designed for non-magnum primers is good way to get a medical bill or at the least a Gunsmith bill. The M41 is a Milspec primer and has a harder primer cup to prevent slamfires and a hotter primer charge to help with cold weather ignition. Having discussed this with Bill at AA and CCI, we have come to the conclusion that the CCI 41 primer is basically the same primer charge as a CCI 450. I have used both in our 6.5 Grendel loads. Have not had any issues with either, except for some rifles with match trigger in which the hammer springs were lighted to decrease trigger pull. Then the Hammer didn't have sufficient energy to ignite the harder M41 Primers. We have since gone to all CCI 450 Primers. One item we did learn is that using Federal primers had a tendency to "empty mags real fast". So they are a no GO!!. Another experience lesson - Always use M41 or M34 Milspec primers in 308 based AR's and compensate for the magnum charge by reducing the charge weight by 10% and working back up from there. (I can tell you how to do that in a gas rifle but that is a another subject!) The firing pins are heavier and they will slamfire a lot easier! Just got done diagnosing that issue with a 243 Win AR we built recently. The 308s didn't have the problem, but the loads we have developed for the 243 did, due to using Benchrest CCI primers. We are working on a firing pin fix to correct the problem.

[Tedward]

We recommend using CCI M41 Primers in all loads for the 5.56 but not for the 223. Using a Magnum Primer with load data designed for non-magnum primers is good way to get a medical bill or at the least a Gunsmith bill. The M41 is a Milspec primer and has a harder primer cup to prevent slamfires and a hotter primer charge to help with cold weather ignition. Having discussed this with Bill at AA and CCI, we have come to the conclusion that the CCI 41 primer is basically the same primer charge as a CCI 450. I have used both in our 6.5 Grendel loads. Have not had any issues with either, except for some rifles with match trigger in which the hammer springs were lighted to decrease trigger pull. Then the Hammer didn't have sufficient energy to ignite the harder M41 Primers. We have since gone to all CCI 450 Primers. One item we did learn is that using Federal primers had a tendency to "empty mags real fast". So they are a no GO!!. Another experience lesson - Always use M41 or M34 Milspec primers in 308 based AR's and compensate for the magnum charge by reducing the charge weight by 10% and working back up from there. (I can tell you how to do that in a gas rifle but that is a another subject!) The firing pins are heavier and they will slamfire a lot easier! Just got done diagnosing that issue with a 243 Win AR we built recently. The 308s didn't have the problem, but the loads we have developed for the 243 did, due to using Benchrest CCI primers. We are working on a firing pin fix to correct the problem.

So with all the info I got lost. Do you recommend CCI 450 Primers? I am trying to get everything to do my reloading and my friend is going to show me how to do it.

Got dies and press now. Need the primers and powder for Hornady 123gr SST's. Drifter said he used 27.7gr AR-Comp with 123gr. A-max. So just the primer info is needed to get started.