Primers effect on velocity

[longwinters]

If all other componants are identical and the primers used are all the standard large rifle (not magnum).  How much variation in velocity have you seen by switching only the primers? Or do primers only potentially effect accuracy?

Long

[Catfish]

There is no real hard and fast rules here. I used to shoot a .270 that I have shot 5 shot groups you could cover with a nickle while not only useing mixed primers, but mixed brands of brass. Other times things vary alot, meaning point of impact and velosity. With .22 Hornet cases you can blow the bullet into the rifleings befor the powder starts burning with mag. primers and this can lead to blowing up a gun.

[Mikey]

I have long thought that the use of either magnum or standard large rifle primers has little or no effect on accuracy or velocity, in large case capacities.  

In short cases or pistol calibers however you will notice a marked difference in accuracy and velocity.  The 22 Hornet situation Catfish mentioned is a great example - that is a small case and a magnum primer will have a more noticeable effect, and a more negative effect than will a standard primer.  Mikey.

[Racepres]

I know for sure (hard lesson) that if you work up a max. load in a ctg. like the 357 Herrett and change the primer to a magnum, you Will!! have very high pressure.... a bad deal ...  But I have seen very little to NO difference when changing primer brand..    Marty

[Iowegan]

I've chronographed a lot of loads using both standard and magnum primers. The results are mixed. Sometimes it makes very little or no difference and sometime it can change things a lot.

What you need to do is shoot your loads over a chronograph. Look for a change in velocity but more importantly, the velocity spread from highest to lowest. The purpose of a mag primer is not to increase velocity but to get better ignition so your powder burns more consistent. Mag primers do produce slightly more energy so you may have to back off the powder charge a grain or so. Generally, the slower the powder burn rate, the more need there is for a magnum primer.

I always recommend using a powder burn rate chart in conjunction with a good reloading manual (or 2).  See: http://www.varmintal.com/pburn.htm
Rifle powders start at #58. The higher the number, the slower the burn rate.

The case volume has a lot to do with burn rate too. A powder that would be considered slow burning in a small case might be way too fast in a large case. Your reloading manual gives some good clues too. Look at the listed powders for a given bullet weight. The more powder it takes to generate the same velocity, the slower it burns.

[Duffy]

I've chased this one around awhile too. A strange one that I've run across lately is in my K-Hornet. With a WW small rifle primer, 11.5g of 296 and a 40g Hornady V-max I get a av vel of 2621. When I switch to a WW small pistol primer the av vel is 2718-2723 and accuracy is better. The extreme spread also drops from in the 60's to around 20. In my 708 if I use WLR primers I get better vel but with Fed GM Match the accuracy is better and I only lose about 40 fps. The most I've seen is around 150 fps from just different brands not reg VS Magnums so there is a difference! As you can tell I try different ones with different loads/guns to find the nitch.

[Val]

In some of my loads changing the primers made no noticeable difference. In others it affected accuracy and in others it affected muzzle velocities. You need to try the loads with different primers to determine the effect.

[myronman3]

in short,  yes they make a considerable difference.  brands matter, too.  cci has given me the best velocities.

[Bullseye]

This is a confusing issue for me.  I loaded 41M, 44M and 357Max for years with Magnum primers because that is what Speers book called for with IMR 4227 (although most other books call out standard primers). Their latest book changed all these to standard primers, so I switched when out of primers.  Big mistake, my POI moved a bunch in all three calibers and the groups size at least doubled.  So now I am back to Magnum Primers per the old book.  Some sources say to use Magnum primers in the 25-06 since it uses such slow powder, but most sources say to use standard primers.  Who the heck knows.  I also hate that books call out so many different brands of primers, I cannot stock all those.  I use exclusively CCI and start out low and work up.

However the Magnum - Standard issue is still as clear as mud to me.

And no matter what I do does not mean anyone else should do likewise!!!

[Mac11700]

From the Lymans 48th edition reloading handbook

The variations in primer sizes and types can create substantial variations in ballistic uniformity.For example: In one primer test,extreme velocity variation was an excellent 38fps.With another brand primer,the extreme velocity variation was a poor 133fps.Pressure comparisions for the same teat loads showed spreads of as little as 3,500psi. with the first primer and a very poor 9,300 psi with the second primer.Obviously,varying the primer can result in noticeable performance variation,ranging from ideal all the way to undesirable.

Add that 9,300 PSI to a already max load...not good...not good at all....


Mac