doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Equation Relating Powder Temperature To P&V

Hello!

Is there a good general equation that relates powder temperature to chamber pressure and muzzle velocity? I know there are very specific ones for large artillary, tank and battleship guns but do not recall having seen even a general one for nitro powders used in shotguns.

I can imagine there might be differences in such equations for single base, double base, etc. powders, maybe even for powders of quite different burn rate or retardant coatings. Such equations would seem nice things to have when working up low chamber pressure loads for summer use and would like to know how well this load might perform in fall and winter. Presently some of us add a grain or two or even three to our low pressure summer loads for shooting in icy temperatures.

Thanks,
Niklas

Good question. Unfortunately, common powders used for reloading are too individualistic for there to be a common performance factor based on temperature.

Certainly, at level of accuracy needed and acheived for accurate long range shooting from rifled cannons, even shotgun powders are too diverse to allow similarly accurate equations. However, I suspect that a usefull parametered set of equations could be derived for popular types of shotgun powders. And I would think that powder makers know something about this, really, they have to. Presume that there is no incentive for them to make even generalized informations available to reloaders, hence we never see that information.

One could derive some rather usefull data simply by having a few popular low-pressure loads P&V tested at a range of powder temperatures, say from +40C down to -20C. With max of 6-7 data points over this range of temperatures, at even ten dollars per shot, would cost much less than what most folks on this board spend on a single gun, or even "inexpensive", 300 dollar repairs. With some smart decisions, a very informative testing program could be designed.

Niklas

Might I suggest you contact Tom Armbrust to suggest the idea for a future Double Gun Journal article.

Rocketman:

I was awaiting your answer to see if you could combine, in a general sense, PV=nRT & F=ma.

Kind Regards,

Raimey
rse

builder,

I have some still developing ideas sort of along that line. There would seem a nice overlap with 16 gauge low pressure loading group interests and Tom's large store of knowledge and test results. RWG, any ideas?

Doubt there would be much advantage to us individual reloaders for doing this with published, powder-makers' loading data. Those data have already been tested to perform adequately over a normal range of field temperatures.

Conversely, many of us have our experiences with nice low-pressure loads that gave bloopers on cool fall and cold winter hunts. We also have learned from such experiences that loading to somewhat higher chamber pressures (say 9K psi vs 7,5K), at nominal 75F (or whatever) temperatures, can save us these embarasments. It would sure be nice to have a better underpinning for such loading practices, as well as predictive ability to know when bloopers await us on cool and cold hunting days.

Raimey,
PV=nRT is right equation for this. Unfortunately, in real world of complex gas mixes (that do not follow perfect gas "law" all that well) and very rapidly changing Ps and Vs, things get real messy real fast. One might use modified PV=nRT to extrapolate a bit from a set of Tom A's P&V tests.

Niklas

I think we are looking at the powder's "k factor" which relates burn rate to pressure. The cited gas laws apply, but are very complex as the powder is in an environment of constantly changing volume, pressure, and temperature. If the combination of pressure and burn rate can't get ahead of the increasing volume, you get a blooper.

I suspect that product liability is major disincentive for the powder makers to supply any temperature dependant data.

Hogden Extreme powders I believe have supplied temperature data.

After one of those embarasing happenings on a "Cold" winter duck hunt with a load taken directly from the powder makers data @ a 7K psi level, I no longer go afield with loads showing less than about 8K & use the fastest powder & hottest primer which can be loaded to a desirable load within those parameters. Have had no problems since adapting this criteria. I have noted over the years that Hercules/Alliant data has showed an "Extremely Limited" number of loads with less than about 7500 psi & these were always listed as "Target" loads. Reckon there may have been a reason?? Other makers did not seem to be quite so "Honest", which resulted in my embarasing moment. The load had been a particularly effective one "Untill" the temps dropped. This load incidently used a rather slow powder in combination with a mild primer but was a 1¼oz (12ga) load & in the makers "Field" section, not a load developed for clay target shooting.

Learned my lesson about going to too low chamber pressure in 1960s when goose hunting on Texas Gulf coast. For a couple of years I had been using heavy shot - low velocity hand loads and doing quite well. I had also been slowly decreasing amount of powder and noticing how well pellets penetrated and killed geese. So far, so good. Then one morning there was a bit of ice on marsh weeds!!! BLOOPERS on every shot -- fortunately no wads stuck in chokes. I think at least one goose actually laughed......


Increased that lowest load by 2,0 grains of slow powder and never had problem again. Powder was Blue Dot, loaded to well below Hercules listed magnum loads.

After that experience, I increased my them preferred 12 gauge hunting load of 1 1/4 oz shot, propelled by enough IMRSR7625 to give about 1150 fps, by two grains for cool and cold weather hunting. Never had a problem, even well below freezing.

Niklas