Magnum vs Standard Primers

[Steven_CO]

Folks,

I tried to search for the answer to my question, but could not find the data and/or can't remember where I read it, so I thought I would throw it out here.

At what point do most decide to go with magnum primers vs standard primers in rifles?

I usually follow the recommendations of the manuals, but in some combinations, it's not that obvious.

As a rule, I have always assumed that over 70 gns and slower burning powders, like RL22, (I guess I could say when using a powder with a burning rate factor of less than 0.40) it's time to go bump it up to magnum primers.

Does anyone else have a better source than my simplified rule of thumb?

[devildoc]

Well it's not a cut and dry thing. I'm sure you may absolutely need a mag primer in some of the monster cases like the RUMs and cartridges based on the .378wby and .408CT, But in my experience the cartridges based on the .375H&H case will take either mag or standard LR primers. Some load combos like mags some like standards.

[Fiftydriver]

My rule of thumb is not all that clear cut either but her goes.

When to use magnum primers:

-When the case capacity is over 85 grains of stick powder
-When the rifle will be used in temps below zero and especially below zero
-When using more then 70 grains of ball powder(except Ramshot powders)

Other possible times to try a magnum primer:

-When velocity spreads are high and can not be decreased by bullet seating depth adjustment

Other then that I generally use standard rifle primers.

Kirby Allen(50)

[MagnumManiac]

Steven CO,
I use magnum primers in ALL ball powder loads, regardless of case size.I don't specifically look at case size as the pre-determinate either.If it is a case like the 25-06 Rem, I look at it's expansion ratio to determine whether or not to use a magnum primer or not.In this instance I use magnum primers for ALL powder types.The reason is because you need slow powders with this cartridge for it to perform correctly.
In my other 06 based cases I use standard primers because the expansion ratio is lower,therefore more efficient.
In magnum cases of any size I use magnum primers regardless, because when you are using very slow powders,under ignition is always high on the possibilities of something going awry.
You can check this with a chronograph very easily.
If you get big differences in velocity with a standard primer, then it's a good bet the powder in some cases is under igniting.
Hope this helps.
MagnumManiac

[overbore]

May produce up to about 27% greater pressure than mild LR primers!!. I was taught, long years ago, "use magnums with 4831 and slower powders" but I agree that low temperatures and 4350 may require them. If we link the slow powder types to magnums, we then automatically cover the large capacity cases but I strongly disagree with their use on ball powders. Overbore

[MagnumManiac]

Originally Posted by overbore

May produce up to about 27% greater pressure than mild long range primers!!. I was taught, long years ago, "use magnums with 4831 and slower powders" but I agree that low temperatures and 4350 may require them. If we link the slow powder types to magnums, we then automatically cover the large capacity cases but I strongly disagree with their use on ball powders. Overbore

Overbore,
I don't understand why you 'strongly disagree' with using magnum primers with ball powders.
My understanding of their make-up is that to change their burning rate,they are either made flatter,which increases the surface area,so they burn slower,or they are made smaller,which reduces their surface area,so they burn faster.
The other factor they use to alter burning rates is the amount of deterrent coating they add to get the correct amount of burn rate.
This significantly makes these powders harder to ignite than 'normal' stick or flake powders.
Every ballistician I have spoken to says that a magnum primer with these powders is to be used,regardless of case size.
If I am incorrect in these facts please show me some evidence to the contrary.
MagnumManiac

[overbore]

for military applications of ball powder are / were not magnums. I am referring to Nam area and the Mouse Gun. Overbore