Magnum primers vs. standard - differences?

M

MagnumWill

New member
I’ve recently picked up reloading (finally), and i’m currently starting with my mountain of 5.56 brass. I’ve looked over the ‘net a few times when reading about magnum primers versus standard, and the only consensus I can find is that if you switch to a magnum primer, start back at minimum, that’s absolutely been stated ad nauseum... it’ll be stated again here, i’m sure - but that’s not my question.

Is there any difference between standard and magnum primers when it comes to pressures within the cartridge itself? I.e. it’s been stated that you use a magnum primer when you have 40+ grains sof powder, but what if the cartridge is of higher pressure? Do the magnum primers hold up better against blowout at maximum loads versus standard primers? They’re also stated as being more sensitive, does that mean hey’re more susceptible to moisture?

Those are a couple questions I haven’t found answers to. I currently have a couple boxes of Remington 7.5 primers, and it seems like people have an adversity to using 6.5 primers in 5.56... so I was wondering, if I haven’t started any load yet, why not use magnum primers specifically from here on out?
 
Lol! It was actually when I got my first revolver, now it’s just serendipitous :)

Again, I have no preference about using magnum primers or not, just trying to find out what the differences are.
 
In 2006, Charles Petty showed that primer choice, shooting a 55 grain A-max over 24 grains of Reloader 10X, would range velocity from 3150 fps to 3300 fps. It would take about 5.5% more powder to do that, which raises pressure about about 19%. However, adding powder adds to post-peak acceleration by making a larger total quantity of gas. Doing it with the same amount of powder, as he did, indicates peak pressure increasing about 26% by modeling in QuickLOAD. So, the answer is, yes, it can make quite a difference. I would drop the powder charge 10% in going from a standard to a magnum primer. Using a chronograph, if you have one, carefully work back up until velocity matches what you had from that exact same powder lot with the milder primer.

I've also seen data from a number of tests with large rifle primers showing much less difference results in switching those around. It probably has to do with the greater capacities of cases made to use them, the difference in those capacities being greater than the difference in the amount of priming material used in the two sizes. I would not count on it to be true with smaller capacity cases that use them.

What a magnum primer does is make more gas than a standard primer. This was originally just to raise start pressure to an adequate level in the larger capacity magnum cases. Subsequently, it has also proven helpful with powders that are harder to ignite. Many spherical propellants are in that category and perform more consistently with magnum primers. in a case where you have extra air space due to lower case fill, as a number of .30-06 Garand loads do, magnum primers can improve ignition consistency.

I recommend reading this artricle on primers.
 
Outstanding, thank you both! That’s the kind of information I was looking for. All I was finding is people prattling on about decreasing the load, without mentioning why or how.

Those reads were perfect, thank you.
 
I ran a ad hoc test with some handloads in my 20" Colt H-bar and my 16" RRA build... 69grn bullet and a charge of H335. Some data suggests a magnum primer with H335, some don't. I don't think it really matters in the tiny .223 case, unless maybe if it's a compressed load or such. Either way, just work up to the load.

Anyway...

I loaded 10 rds each with CCI mag 450's and std 400's, 23.5grn H335 in new LC cases, all under a Sierra 69grn MK BTHP with a light taper crimp... here's what I found:

Standard primer:

16" RRA midlength upper, avg 5rd velocity: 2586fps, SD 24fps
20" Colt H-bar, avg 5rd velocity: 2673fps, SD 16fps

Magnum primer:

16" RRA midlength upper, avg 5rd velocity: 2561fps, SD 27fps
20" Colt H-bar, avg 5rd velocity: 2668fps, SD 31fps

Oddly enough, I got more velocity... and more consistent velocity... using the standard primers, even in the short barreled carbine. Whooda thunk?

It would be interesting to do the same type of test with something bigger, like a .308, to see if the larger charge of ball powder realllly needed that magnum primer.

As an aside, I use CCI Arsenal primers in both my AR 5.56mm loads, and my 7.62 M1a loads. The arsenal primers have a harder cup specifically to deter slam-fires on a high primer or with a floating firing pin, like in the AR. They are considered magnum-equivalent. Is it necessary? Probably not, given my reloading technique, but I have them and my load data is worked up with them, soooo that's where I'm at.
 
Tagging along with what Unclenick said:

I use H335 in my 45-70. Speer recommended using a magnum primer with that powder due to spherical powder being more difficult to ignite..... especially if it's cold.

I use magnum primers exclusively in my 5.56 AR loads due to harder cups. I have not personally tested for velocity difference between standard or magnum primers.
 
Charlie 98 said:
Oddly enough, I got more velocity... and more consistent velocity... using the standard primers, even in the short barreled carbine. Whooda thunk?
Click to expand...

Yes! QuickLOAD's author points out this can happen as well. There are a couple of reasons. One is how the extra gas production is achieved, whether by increasing the amount of standard priming compound or by sticking with the original dose but adding fuel compounds. The latter results in more gas, but lower brissance. In small cases, like the 22 Hornet, the primer can then unseat the bullet before the powder pressure does, causing erratic ignition. So, the resulting effect of a magnum primer on the load is not entirely predictable. You must assume the worst, reducing the charge, and then work back up until you can see what is really happening in your particular case. Regardless of how much powder is required to achieve a given velocity with a given primer, go with the primer that results in the lowest velocity SD, as it is achieving the most consistent ignition.
 
It sounds like all sorts of strange things can happen... especially how the article mentioned the presence of a double pressure spike when the primer ignition is enough to unseat the bullet and start sending it on it’s way before the powder’s burning...

So far the “slowest” powder I have is CFE 223, which may be a good one to start with in a nice low charge whilst using the Remington 7.5 primers.
 
Slow powders get even harder to ignite in small charges and need more pressure to burn completely and cleanly. Primers unseating bullets are more possible in this situation because of the greater length of time pressure takes to build, though it is more common in very small capacity cases.

You will note that Charlie 98's results show the additional possibility that nothing very significant happens. His differences, while monotonic, are well within random error possibilities for the 20" barrel and are only separated by about one standard deviation for the 16" barrel, so there is some significant overlap in the bell curves of the velocity distributions. You need samples of more like 30 rounds to get a clear view of real differences when they are that close.
 
MagnumWill wrote:
Magnum primers vs. standard - differences?
Click to expand...

The active ingredient in most primers, lead styphnate, is an explosive. When subjected to the sudden shock of the firing pin crushing the "pellet" of explosive under the primer's anvil, it explodes. The explosion is in the form of hot gas expanding at about 16,000 feet per second. The heat of the gas is sufficient to start the nitrocellulose propellant burning.

The difference between a standard and a magnum primers is a slight (very slight) difference in the size of the lead styphnate "pellet" that makes the explosion of a magnum primer a little larger.

Is there any difference between standard and magnum primers when it comes to pressures within the cartridge itself?
Click to expand...

There can be.

The pressure differences - and they can end up being higher or lower - are generally accountable under the mechanisms of:
  • A primer ignition is of sufficient force to launch the bullet out of the case and well down the barrel on its own, so a more forceful primer ignition can start the bullet moving sooner than if a standard primer were used. This could result in lower pressures attributable to the fact there is more volume in the cartridge case since the bullet has already started to move. Alternatively, if the primer ignition moves the bullet forward so that it engages the rifling and pressure in the case has to rise enough to simultaneously overcome the inertia of the bullet and the resistance of the rifling, the pressure could be higher.
  • A magnum primers can cause the powder charge to more completely ignite thus resulting in the pressure and temperature in the case (pressure and temperature both have an effect on how fast the powder burns) rising more rapidly than if a standard primer was used.
  • The more forceful ignition of the magnum primer can cause the powder charge to be blown around inside the case 1) more evenly, or 2) into a concentration at one end of the case resulting in faster or slower ignition with corresponding changes in pressure.
There can be other mechanisms at work as well, but these three will give you an idea of what can be going on inside the chamber when the firing pin hits the primer. All of these effects can and will be going on in any particular cartridge to some extent each time it is fired. How significant each one of them is dependent upon a host of variables, which is why the recommendations in published data should be followed.
 
MagnumWill wrote:
So far the “slowest” powder I have is CFE 223...
Click to expand...

Powder burn rates are dependent upon the temperature and pressure at which they combust. There is no industry standard for determining "burn rate" so what one manufacturer rates as a "fast" powder may not be so fast when determined under the method used by another.

This comes across quite clearly if you compare the burn rate chart in Vihta Vuori's (VV) Reloading Guide #12 with the chart on Hodgdon's web site. VV says the fastest powder is Hodgdon's Titewad while Hodgdon says it is Norma R1 (with Titewad coming in at 6th place).
 
"...when it comes to pressures..." It's a very decided maybe.
"...magnum primers hold up better..." No. The only difference between a magnum primer and a standard primer is the priming compound.
"...magnum primer does is make more gas..." They make no gas at all. They merely burn a bit hotter for a bit longer. Their purpose is to light hard to ignite powders.
Remington 7.5 primers are Bench Rest primers, not magnum primers. According to Midway, Remington says to use their 7.5's in 17 Remington, 222 Remington, 223 Remington, 204 Ruger, 17 Remington Fireball and not their 6.5's. Remington doesn't actually make a small rifle magnum primer.
 
What are you looking to gain by using mag primer's. I'll switch brands but don't switch to mag from standard when loading data calls for one or the other.
 
You will note that Charlie 98's results show the additional possibility that nothing very significant happens. His differences, while monotonic, are well within random error possibilities for the 20" barrel and are only separated by about one standard deviation for the 16" barrel, so there is some significant overlap in the bell curves of the velocity distributions. You need samples of more like 30 rounds to get a clear view of real differences when they are that close.
Click to expand...

Oddly enough, I was surprised that there really wasn't that much difference at all, I expected the magnum primers to at least match the FPS readings. As I mentioned, given what I have read since, there might be a more pronounced difference in a bigger round, or an even longer barrel. I suppose I might do the same thing with my 16" M1a and my 24" Savage some day.
 
What are you looking to gain by using mag primer's. I'll switch brands but don't switch to mag from standard when loading data calls for one or the other.
Click to expand...

Reports of flattened primers when using 6.5 primers versus 7.5 in .223 is what started me on the path. Beyond that, i don’t have any disposition towards them. Regardless, i’ve learned a lot from this thread for sure - thanks for everyone’s input.
 
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