Rifle Powder question

[rbernie]

Hodgden advertises some of their extruded powders as demonstrating less temperature-related velocity variance than other powders. I'm curious if anyone else has encountered any data that quantifies the relative temperature variances of rifle powders?

 

[Jim Watson]

Years ago, before Hodgdon went to their current line of powders made by ADI, I read an article describing temperature sensitivity tests done by putting ammo in a refrigerator and carrying it to the range in a picnic cooler and shooting it versus ambient ammo.

Sounds like it might be time for an update.
You wanna break into gunzine writing?

 

[Jaywalker]

Quantitative, no, but writer John Barsness has written that he has seen drops in standard, temperature sensitive powders of 200 feet per second between 70F and 30F. He writes that the "less temperature-sensitive" (e.g., Hodgdon Extreme and Ramshot's whole line) show no measurable difference between those two temperatures.

One temperature difference that usually goes unrecognized, however, is at the range when dialing in a new load. The receiver and barrel heat up, and the cartridge absorbs the heat. My reloads using Hodgdon's Extreme line tend to wander significantly less under these circucmstances, though I would not call it "zero difference." As this is several hundred degrees, however, it's a pretty stiff test.

Jaywalker

 

[taliv]

rbernie, i asked that question about a year ago to the sierra technical hotline and their response was that a double-base nitro glycerine powder averages 2 fps per degree change. i.e. expect 80 fps less velocity at the muzzle at 30deg from what you saw at 70deg.

in addition, the cold would have an affect on density of the air, and humidity, which would also affect the trajectory. but i wouldn't include those factors in any calculation (even if i knew how)

sierra allowed as how single-base powders have less variance than the double-base variety.


as another piece of data, the ballisticard for fed 308 168g bthp match @ 2640 fps shows the following MOA with a 100yrd zero

..........30deg.....60deg......90deg
200yrd......2.0......1.9......1.9
600yrd......16.4.....15.8......15.2
1000yrd......41.6.....39.3......37.1

shouldn't be hard for you to reverse engineer those numbers to find the difference in velocity that would be required to make a 2.3MOA difference between 30 and 60 degrees at 1000yrds.

 

[rbernie]

What I'm wrestling with is the fact that I don't have a chronograph and am trying to finalize some standard loadings.

I've been working up loads for my 7x57 and 303 and 223 Rem, based upon a multitude of recipes. I've been making five-round batches of LOTS of combinations of powder and bullets for a given chambering, and using lots and lots of range time to select the ones that show the most promise from an accuracy perspective. I'm reaching the end of this 'data collection' process, and this is where things get sticky. For example, now that I have a couple of different loads for the 120gr Hornady in my 7x57 that should be (by the book) relatively comparable in velocity and which have proven identical in terms of accuracy, the question arises as to which load will be more consistent under the most conditions. Without a chrono, I'm pretty much stuck with making this a paper analysis.

Put more succinctly - if I have two recipes (one using, say H414 and one using RE19) that produce equal accuracy and relatively equal velocity, I'd like to standardize on the one that's most consistent under more conditions than the other.

 

[squirrelsniper]

Although most people consider it strange these days, I rarely chrono a load, so I can't give you any velocity data. However, I use a few of my rifles for long range shooting and I've really begun to like the "Extreme" series of powders. I shoot in temps from in the 90s during the summer down to temps in the 20s during the winter. At ranges from about 500yds and farther, any velocity change really shows up as a change in POI. With the Extreme powders I'm currently using (Varget and H1000), the POI change from one temp to another is only about what you would expect for the change in air density, so evidentally the velocity is remaining quite stable from one temp to another.