Low pressure powder choices updated

[steve white]

In studying XXL provided load data for 375 H&H, 30'06, 7x57 I was astounded to find several powders that regularly gave pressure readings 8-10 thousand LESS psi than all others listed. Rel 23 (stellar), Vit N555, Accurate 3100, Lovex S071, H Hybrid 100v were regularly listed at 35K psi- 39K psi across many loads in all three (widely divergent) calibers above! And in checking other calibers on my wish list, the trend seemed to hold, within bullet weight parameters of course. In other words, these seem to plainly be low pressure powders. In some applications, old standbys like 4831 and MRP kept pressures lower, too, and moving up in bullet weight sometimes bumped selection from Rel 23 to Rel 25, etc. But many of the "temp sensitive" powders gave so much pressure comparably that it almost made the point moot.
Why worry about temperature sensitivity if you can keep pressures this low In the first place?
I'm thinking about not only applications for African heat, but for use in break action rifles and older Mannlicher Schoenauer rifles among others which can do without the stress and strain of hotter loads.
The only problem I am finding is locating enough commonly available published data--the kind you don't pay $30 a month to obtain, in applying these powders to above applications. If any of you have favorite LOW PRESSURE loads, please feel free to share. (with the usual safety disclaimers)

 

[wswolf]

Reloder 23 and Vit N555 (and all Vihtavuori powders for that matter) are designed to be temperature resistant.
Many modern powders, by design, burn most consistently and provide their best accuracy at 60,000 to 65,000psi and might show poor accuracy at low pressure.
Powders whose velocity varies a great deal with temperature might cause the point of impact to shift by several inches as temperature varies.
John Barsness, who has done the experiments, found that temp resistant powders show negligible change in velocity from slightly below zero F. to about 80 F. He found that above 80 F. all powders increase pressure as temps increase but the the temp resistant powders not as much.
In conditions where temperature is a concern I prefer temperature resistant powders and test them at the highest temperature that I expect to encounter.

 

[fourfive8]

Two reasons to use temperature insensitive powders. Less variability with temperature swings and avoiding having to use a 2x4 to beat a bolt open at the worst time possible if ammo/gun get slightly over-heated. Simple- no mystery.

 

[steve white]

Granted on temp resistance, but why not loads which run on the high end are still 10k psi below others? Not all guns can handle 65K psi

 

[Bob Nelson 35Whelen]

Two reasons to use temperature insensitive powders. Less variability with temperature swings and avoiding having to use a 2x4 to beat a bolt open at the worst time possible if ammo/gun get slightly over-heated. Simple- no mystery.

@fourfive8
That's why I try and do my load development in summer and them check my sightings in winter. ADI powders we get in Australia and sell to hogdon are supposedly temp stable. The other 2 powders I use Hodgdon Superformance and CFE223 have given me problems in our cold weather or hot weather. Even in Namibia with tems of 38 degrees celcieus/100 degrees Fahrenheit I had no issues with CFE223.
Bob

 

[steve white]

I guess I got us chasing the wrong rabbit with my remarks about temp insensitive powders. What I really wanted to investigate was how much better it would be to load up the lower pressure powders. It would possibly allow one to reach higher velocities/accuracy nodes before tapping out due to pressures too high for a break action gun, for example? In other words would it also allow higher velocities to be reached because being overpressure would not be so much a concern?
BTW, I have found any number of 30'06 loads for the N555 powder. Still trying to find info for all my calibers for the Rel 23.

 

[fourfive8]

Aha ok. I think I see where you are coming from. From a pressure standpoint only, there are powders usable in many cartridges that, when loaded to high,100% or even compressed load density, produce pressure well under normal max rating for that cartridge/action. In that sense, yes that creates kind of a built-in insurance against over pressure. The downside I think is sometimes, depending on overall cartridge design or bullets weight, that can create an inconsistent burn/pressure situation which may cause accuracy issues. Or of course depending on cartridge design, pressure too low may never reach desired bullet velocity. It's my understanding that is the way progressive powders work and the reason most cartridges/bullet weights do best within a certain range of powders/burn rates. It's my understanding that is one the unforeseen coincidental benefits of the 416 Rigby cartridge design when used with modern powders. Its design falls within the range of shape, volume and bullet mass where several slow burning modern progressive powders produce low max pressure, adequate bullet velocity and acceptable accuracy. It was designed around the common smokeless powder available at the time, cordite, which was very temperature sensitive.

One caution I'm aware of however with some cartridge designs using smaller volumes a slow powder, particularly a slow ball powder is setting up the potential for a secondary explosive event or SEE. Even though on paper the slow powder should create low pressure under a normal progressive burn curve, a total potential chemical energy still exists in any given powder charge. If that potential energy for whatever reason is released all at once in can create the SEE. The circumstance that casue the SEE are still not well understood, but appear to be real and not something to ignore.