Primers, Temperature and Pressure

J

Jack Roberts

Moderator - Deceased
In the latest Varmint Hunter magazine Denton Bramwell continues some experiments he has been working on to discover how temperature affects pressure and velocity of rounds. He reports some results which are counter-intuitive.

Changing brands of primers and even switching between regular and magnum primers has absolutely no measurable effect on pressure or velocity. That sure is not what we have been lead to believe for many years.

Changing the temperature of a primer has absolutely no measurable effect on pressure or velocity. He fired primers at temperatures from -60F to +79F.

He does caution that these results may not hold for all calibers, larger or smaller cases could possibly show different results. The cases he tested were 243 and 30-06.

Jack
 
How can different primers not affect pressure or velocity when one burns hotter than the other? How could just changing primers in a load change the way the load shoots if nothing is affected?
 
Hi Jack...

I have NOT tested all combinations of primers/powders, but I have found that there is little or no difference most of the time. definitly not enough to warrent the "drop 10% and work up" approach.

I have found absolutly no difference between Rem 7-1/2 and BR-4, either in velocity or accuracy. I even mixed the two and shot groups that were equal to either one alone (in good rifles).

I have never had an increase in velocity with substituting magnum primers.

This is NOT a definitive statement for all primers, but I no longer worry about substituting them.

.
 
Quote:
How can different primers not affect pressure or velocity when one burns hotter than the other? How could just changing primers in a load change the way the load shoots if nothing is affected?



Think of as this way, the primer is a lot like the spark plugs in a motor, I provides energy for the ignition but it's not the fuel that drives the motor. By changing to a different brand, it rarely have any effect to the over all performance.
 
Jack, I've NEVER doubted anything you have said here, and I have the utmost respect for your knowledge. /ubbthreads/images/graemlins/wink.gif

BUT...YOU are one of the guys who says to go by the book. And you know that danger awaits those of us who are foolish enough to start experimenting without a hypothesis that is based upon ballistic facts.

Until I see more of this, based on factual evidence that is coming from more than one person's experiences and tests, I'm going to go by the "tried & true" for a while longer. /ubbthreads/images/graemlins/grinning-smiley-006.gif
 
I've done some limited experimenting over the years, since I've owned a chronograph. I have no access to any sophisticated pressure testing equipment, either.
What I have found, in some instances, is the size of groups changing with different primers, all else being equal. I've also noted larger ES in velocity with one brand of primer over another, all other things being equal. This was never consistent to brand in all cases, but to cartridge/load combinations. I've never noted a significant difference in average velocity when switching primers, all else being equal in that same load.
I have seen fluctuations in velocity, in the same loading, when fired at different outside temperatures, especially when the temps differ over 40 degrees...with some powders. Pressure signs have also changed with radical temperature changes...with certain powders. It ain't an exact science....caution, attention, and common sense should prevail!
F1
 
Read the article.
The guy seems to use pretty reliable lab technique.

I can say that because in a former life I was a lab technician and a chemical engineer. I gave that up because it didn't pay well but still remember what makes reliable and repeatable tests.

He didn't do it perfectly, but pretty good.

Jack
 
Jack,

I also read that article. It was enlightening.
I know Denton and his findings are accurate from a test set up viewpoint. I have no problem with what he found as a result of his testing, and accept what he found.
Denton is a very intelligent man who is technically trained and has good lab techniques.

Martyn
 
Hi All,
From my own experience with a 22-250 I have found there to be a significant difference between magnum primers and large rifle primers in their effect on the pressure, POI and drop over larger distances.

When I first started out loading my own (not that long ago) the guy behind the counter said he didn't have any Fed GM210's so he sold me 215 (magnums). He said there was no differnce in effect.

I couldn't get within a bull's roar of my upper load limits without significant pressure signs. I then did some research and found that the magnum primers are NOT recommended for large rifle application. I suppose I found out why the hard way.

Everybody has to do what they think is right, but I learnt my lesson with magnum primers.
 
Don't doubt his findings at all. Personally I never thought it made much difference but had no interest in bucking conventional wisdom. Back before the 'internet' and mass information at the touch of a keyboard sometimes we just had to function with trial and error.
 


Write your reply...
Back
Top