Std primer to Mag primer conversion. Can you verify?

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WyoGunner

Single-Sixer
Joined
May 27, 2009
Messages
193
A member of another forum said that he had a load book that mentioned that mag primers could be switched for standard primers at starting loads by dropping the load by 5%. Or in other words, one could take a load that was listed with a small pistol primer and multiply it by 105% to determine an equivalent load using a small pistol mag primer. Can anyone else verify this?

Source: http://www.thefirearmsforum.com/showthread.php?t=63300
 

dougader

Hunter
Joined
Jun 18, 2008
Messages
3,108
I've never seen that before.

I think its necessary to have those loads pressure tested to verify something like that. There are differences in primers from different companies. Lot to lot differences in primers may cause more difference than that.

IMO that's a pretty broad statement that requires more than a simple 5% formula to compare one primer to another.
 

Rex Driver

Bearcat
Joined
Oct 8, 2007
Messages
60
Much like selling my reloads (which I will not) I do not offer this advice as a go for anybody else, however, it has worked for me.

First you have to remember that most of my reloads are cowboy type loads 38spl with 3.3 Grains of Winchester 231 behind a 125 Grain Bullet, either RNFP or FPs. During the past year primers have been in somewhat short supply (I think we can all agree on that) and I have used several brands to include Federal Small Pistol, Federal Magnum Small Pistol, Winchester and Remington, all with very good results and very little change in velocity and recoil. I have always gone on the idea that the main difference in regular and magnum in small pistol primers is about .2 grains of Winchester 231 and since my loads boarder on the "Mouse Phart" side of the equation have not worried too much about variation of primers.

Now, having said that, I do load a fair amount of loads that meet power criteria for CORE and IDPA matches and use 4.4 Grains of the same Winchester 231 behind 158 Grain RNFP bullets and on these I only use Federal Primers to both keep pressure constant and because I have springs in my GP 100s that do not like Winchester or CCI primers.

Now that components are getting a little easier to find perhaps I will again become more picky as to staying with one primer brand but for the past year I have even used CCI reclaimed from years old PPC ammo that I have pulled for Practice.

Perhaps some will cringe with my statements, however, at almost 62 years of age and 36 of them going to the range on a semi regular basis, I still have both hands, all ten fingers and both eyes. I am either lucky or doing SOMETHING right.
 

Three44s

Single-Sixer
Joined
Apr 7, 2005
Messages
303
I treat a primer change just like any other load change ........

........ START OVER!

Three 44s
 

edlmann

Blackhawk
Joined
Apr 6, 2009
Messages
785
WyoGunner":35bru36c said:
A member of another forum said that he had a load book that mentioned that mag primers could be switched for standard primers at starting loads by dropping the load by 5%. Or in other words, one could take a load that was listed with a small pistol primer and multiply it by 105% to determine an equivalent load using a small pistol mag primer.

Uhhhh, no.

If nothing else, it seems to me that if you were converting from standard to magnum primers, you'd divide by 1.05, not multiply.

Also seems like a dumb idea. Start over again.
 

GaSidewinder

Bearcat
Joined
Oct 5, 2009
Messages
32
Here is what the guy on the other forum said

"I do have one manual that states that mag primers can be switched in at the start load level by dropping listed loads by 5%. It might be worth figuring out what the start load was in these loads & multiplying the charge by 105% to see where he is. Hopefully the mag primers didn't put him too high. If it was me (I've been there & done that) I'd shoot one round & see how it extracts. Overpressure loads are easy to spot that way in a revolver."


It's hard for me to figure what he is trying to calculate with the 105% but I don't think he is figuring his load data with it. It looks like he is trying to figure an outcome of either published velocity or pressure. I don't believe either will work out quite like that but I personally don't think there is a problem for an experienced handloader that has worked up loads to substitute magnum for standard primers. I believe that all handloaders should use caution and should check their ammo for any signs of excessive pressure. I don't know that there is a magic number to reduce a starting load by when substituting the primers but I wouldn't personally have a problem with 5% less than the starting load.

I would also say that thousands upon thousands of rounds loaded and fired would give a handloader more of an insight to their own particular situation than a person without that same experience.
 
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