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How does QL or LFAD account for Magnum primers vs Standard primers?

OK...

I decided to call NECO regarding my question.

I was told that when using magnum primers during trials to work up initial loads, add 10% to the "Shot Start (Initialization) Pressure.

From there, it's business as usual. Once actual load results are determined, then go to the "Weighting Factor" and so forth.

Good info AI.

Does this mean they assume standard primers in all loads? Even magnums?

Essentially, that is what I understood him to say.

But, as you know, the software is an approximation. If you are developing a load where you are switching from standard primers to magnum primers, increasing the startup pressure 10% is the method suggested to account for the increase in the pressure simply due to magnum primers.

From there, once you have chronographed your loads and so forth, you'll be able to adjust the weighting factor and startup pressure to better approximate the results from your firearm.

That aside, the margin of error of all other factors is far in excess of the 400 psi difference in startup pressure, from what I can tell. In actuality, it probably is insignificant.

Anyway....

Because nowhere in the world exists reliable data regarding primers, it is impossible to take account for specific primers.
Even in military research there are only a few primer-propellant interface studies known almost for medium (above 20mm) calibers.

Primer manufacturers make their MIL primers according to MIL Std or NATO Stanag to obtain the specified mechanical data and output values. And they make their commercial primers according to their experience.
There have been interesting articels some years ago in "Precision Shooting Annuals" by Mic McPherson regarding primers and pressures, but nobody can tell you if these findings are still valid.

As a rule of thumb one should use rifle magnum primers with spherical powders with a burning rate comparable to H414 and slower and slow extruded powders like 4350 and slower with cartridges of high capacity. Normally magnum primers will give a more consistent ignition with spherical powders (you cannot watch this with chronograph readings).
For handgun cartridges H110, WW296 and Ramshot Enforcer are candidates for pistol magnum primers.

Empirical tests with all the primer-powder availabe have not shown that magnum primers are responsible for higher pressures. Sometimes they produce higher pressures, sometimes even lower.
Over the years primer behaviour changes - so there it is impossible to predict their influence on pressures.

[quote=h_broemel]
"As a rule of thumb one should use rifle magnum primers with spherical powders with a burning rate comparable to H414 and slower and slow extruded powders like 4350 and slower with cartridges of high capacity."

HB,
What is concidered "cartridges of high Cap." ie, the total amount of powder used to the bore size etc, as an example, 22 cal with 60grs+ or 30 caliber with 80grs+ powder capacity etc, or cartridge shape or some other value?

"For handgun cartridges H110, WW296 and Ramshot Enforcer are candidates for pistol magnum primers."

Does case shape,size or amount of powder used, indicate when to use magnum primers?

At this time I am shooting a wildcat in 17 caliber with 12grs or less of WW296, H110 and Ramshot Enforcer powders using Rem 7 1/2 primers only and these are some of the best loads so far, as for accuracy/fps etc.

I would have not considered using a magnum primer under these conditions, using the above powders in a case this small,(5.7x28mm FN).

"Empirical tests with all the primer-powder availabe have not shown that magnum primers are responsible for higher pressures. Sometimes they produce higher pressures, sometimes even lower.
Over the years primer behaviour changes - so there it is impossible to predict their influence on pressures."

I for one greatly appreciate your time and responses in ref to QL questions. Thank you.
Don