IMR 4064 temperature sensitive?

[TheDutchman19]

Does anyone have any experience as to how sensitive IMR 4064 is to low or high temperature?

What temperatures constitutes high or low?

I have been working on a load for a new gun and it loves 4064. The question people ask me is "how is it with extreme temperatures?", to which I answer "I have no idea!"

[chiefr]

One of my favorite powders, I do not consider it temp sensitve in relation to normal temps.
I have never placed any reloaded 4064 ammo in direct sunlight. A process used by those in the military called "cooking" to gain more FPS, but according to mil teaching practically all small arms ammo will behave differently when exposed to extreme temps. Rule of thumb is low temp lessens FPS and High temp increases FPS.

[4runnerman]

I use H4064 in a few loads, Have been told IMR4064 is almost the same just more temp sensitive. Not much help to you at all here.

[jmr40]

Hodgdons line of "Extereme" powders are formulated to be less sensitive to temperature extremes.

http://hodgdon.com/extreme.html

With any other powder you can expect roughly 1 fps difference in velocity for each 1 degree of temperature change. For most people this isn't a huge deal. If you develop a load at 70 * it would be aboout 70 fps slower at 0* with most powder. Unless you are shooting at extreme range 70 fps probably won't effect performance that much. Especially at 200 yards or less.

I prefer to use the Extreme powders. I figure I may never need it, but as long as there are no negatives, why not.

For me I'm more concerned about high temps. I generally spend a lot of time at the range experimenting in the winter when the range is empty. If I develop a load close to max on a day when the temps are in the 30's it might be 70-80 fps faster in August and be an over pressure load in hot weather.

[CharlieDeltaJuliet]

H3000 is a good temperature insensitive powder if it helps. I shoot a 300 WM and replicate the Navy/Army sniping rounds and it uses that powder with great success.

[Jimro]

Does anyone have any experience as to how sensitive IMR 4064 is to low or high temperature?

What temperatures constitutes high or low?

I have been working on a load for a new gun and it loves 4064. The question people ask me is "how is it with extreme temperatures?", to which I answer "I have no idea!"

The answer to you question as posed is "it depends."

In 308 and 30-06 pushing 173~175gr match bullets, standard charges of IMR4064 are very temp insensitive, around 20 fps difference per 100 degrees F in change. This is "about" the same as Varget, which

In any other chambering, I couldn't give you any real data to evaluate.

Jimro

[Bart B.]

Jimro, your two comments:

With any other powder you can expect roughly 1 fps difference in velocity for each 1 degree of temperature change.

In 308 and 30-06 pushing 173~175gr match bullets, standard charges of IMR4064 are very temp insensitive, around 20 fps difference per 100 degrees F in change. This is "about" the same as Varget,...

Why doesn't 1 degree temperature change with IMR4064 change the .308 bullet speed 1 fps in stead of 1/5th fps per 1 degree of change as what the second line above says? Just curious.

I've often had to wait shooting a string of shots in long range matches with the .308 Win. Using IMR4064 powders, if the round stayed in the hot chamber more than 20 seconds, I'd come down 1/4 MOA on the sight to compensate for its higher muzzle velocity. And another 1/4 for every 20 seconds thereafter. I've waited as much as 1.5 minutes time or more coming down about 1.5 MOA on the sight and still shot to point of aim then loading another round, coming back up 1.5 MOA on the sight and shooting that round to point of aim with it staying the chamber no more than 10 to 15 seconds before firing.

[TheDutchman19]

Sounds like a test is in order.

So if I'm shooting in 60 degree weather through a chrono, note the FPS. I could leave a bullet in the chamber for "X" amount of time. Take the round out and measure it's temperature. Load the round and fire.

That should give me some rough idea of the fps spread. Am I over thinking it?

[Bart B.]

Your test's a good one, but I'd get an infra red thermometer to measure barrel temperature at the chamber. That's what's causing the powder inside the case to warm up and shoot bullets out faster. You could leave a round in for a while, then note the chamber area temperature as you ejected it then quickly measure the brass case temperature. The powder temperature will be cooler than the case but as time goes by, the case starts to cool down and so does the powder.

A friend did that some years ago but someone held the IR thermometer near his barrel chamber while he set at the bench loading ammo, letting it rest for different amounts of time then shooting that round's bullet through a chronograph. I no longer remember the exact numbers for fps and barrel temperature versus round time in the barrel, but the velocity increase pretty much agreed with my come downs on the sight for chamber times the round cooked.

A convoluted test, for sure, but one properly done could easily yield some interesting stuff.

[Jimro]

Bart B.

The temp sensitivity is for the powder, not the barrel. Barrel Temp affects ballistics more than ammunition temp: http://www.shootingsoftware.com/ftp/...%20Factors.pdf

When you let your ammo sit in a hot chamber and get hot before being shot down a hot barrel you get the "worst of both worlds" which is why you had to come down 1/4 MOA to stay in the X ring.

If you control for barrel temp, and only test powder temp sensitivity, then you see that most extruded single base powders are fairly "temp insensitive" compared to double base powders, which is why the Navy changed the powder for Mk316 Mod0 to IMR 4064, because it was more "temp stable" than Reloader 15.

As you can see from the linked pdf, even the "Temp Stable" H4350 has a very similar trend line to the "old" IMR 4350. But that is in the caliber tested, and every chambering responds a bit differently.

Jimro

[Bart B.]

Jimro, how does barrel temperature effect ballistics more than powder temperature? Bore and groove diameters get bigger as the barrel heats up; is this what you're referring to? Or is it the structural properties of the barrel itself effecting how rigid it is as it heats up?

[Jimro]

Bart B.

The effect of barrel temperature is around 204 PSI per degree F for the Varget load. Also, the small sample gathered with 4350, before my thermocouple meter went kerflooey, is consistent with this result. Since the 4350 sample is small, the uncertainty is high, but the best estimate is 177 PSI per degree F. If you’re not controlling barrel temperature, you about as well might not bother controlling powder temperature, either. In the cases investigated, barrel temperature is a much stronger variable than powder temperature.

I suspect that the mechanism for the effect of barrel temperature on pressure is from the large thermal mass of the rifle quickly bringing the primer to the same temperature as the chamber, and that what we are seeing really represents primer temperature. That’s the topic of yet another experiment, to come.

The answer to "how" is something I do not know. I do know that it does based on the data available.

If I were to hazard a guess in addition to the primer temp idea, I would say that the thermal expansion of barrel steel (with or without any coatings such as chrome or nitride) causes a difference in the friction coefficient, making the gilding metal jacket "stickier" as it goes down the bore. I have no way of testing that though.

Jimro

[Bart B.]

Jimro, stainless steel expands about .000006" linearly per degree F temperature rise as I remember.

Yet starting out with cold barrels shooting once every 20 seconds for 30 shots doesn't cause and accuracy degradation at long range as bore and groove diameters get a tiny bit larger for several succesive shots. And that's where I think it'll show up first. Same for shooting 10 shots 5 seconds apart starting out with a cold barrel, then repeating that all over after the barrel's cooled down for only a couple minutes; 1/2 MOA accuracy at 300 yards.

All the bore and groove expansion caused by that much temperature change (70 to 160 degrees F, or thereabouts) doesn't seem to effect accuracy at all. But I have observed a slight increase in muzzle velocity starting out with a cold, clean barrel and the 3rd or 4th shot fired leaves a few fps faster due to powder fouling. Same thing with a fouled barrel, muzzle velocity stays the same from shot to shot. But chamber time of the loaded round has to be kept the same.

My tests may not have been 110% perfect and exact, but repeatable enough to show a significant trend.

[Jimro]

Bart B.

That 90 degree swing between 70 and 160 would correspond to a 0.00054" expansion of the barrel. But we have to think of barrels as a series of rods bent into a circle, so what you have done is expand the middle diameter (where the steel is, between inner bore and outer diameter) by 0.00054", which of course would correspond to a smaller internal diameter increase as it has the smallest diameter.

I'm interested to find out if that "3rd and 4th shots are faster" even when you start out with a fouled bore. Do you have any notes on that?

Jimro

[Bart B.]

Jimro, only data I have is remembering that a fouled, cold bore shoots the bullets out at the same speed from 1st to last shot in a 10 to 20 shot string as long as the round's not in the hot chamber for more than 15 seconds before it's fired.

[GeauxTide]

Varget is very close to IMR4064. My favorite load in '06 is with 4064. I've shot it in hot and cold and it never varies at the chrony.

[Jimro]

Jimro, only data I have is remembering that a fouled, cold bore shoots the bullets out at the same speed from 1st to last shot in a 10 to 20 shot string as long as the round's not in the hot chamber for more than 15 seconds before it's fired.

That is interesting, it strongly implies that fouling is more important than barrel temperature in terms of "temperature sensitivity" for powder performance.

Jimro