.308 win - IMR4064 or Varget

[W.E.G.]

Powder: Varget

I actually did a test to see how much difference I could get between ammo that was packed in ice, versus ammo that was placed on a black rubber mat on the hood of a car that had just come off the highway in August.

The hot ammo (hotter by about 75 degrees) was faster by about 50 fps.
Less than one inch deviation at 300 yards.
Which is not enough to matter for any practical application.

See http://www.usrifleteams.com/forums/index.php?showtopic=17858

Did some more hot ammo testing yesterday.

Test:
Determine effect of extreme ammunition temperature on velocity.
Gunpowder tested was VARGET.

RESULTS:

Short version:
Extremely hot ammo (110 degrees) shoots faster than ammo (75 degrees) from shooting stool.
Faster ammo hits higher than cooler ammo by this much:



Keep reading if you want the long version.

Long version:

Rifle used for test: AR-15 rifle with 20” barrel.
Chronograph used for test: Chrony Beta Master.
Software used for bullet-drop calculations: Silhouette Ballistics
No software was used for velocity-estimation. All velocities reported here are actual shots fired over a chronograph.

I attempted to shoot 10-shot strings to gather the chronograph data.
You will notice that the data sets do not all contain 10 shots.
The Chrony chronograph sometimes simply failed to display the velocity.

The load used for the temperature-variation test was 24.2 grains of VARGET with a 75-grain Serbian (Prvi Partisan) bullet loaded to 2.250” “magazine-length.”
This is a compressed load – 108% loading density according to Quickload.
Powder crunches when bullet is seated.
Powder does not rattle when shaken.



COLD AMMO
24.2 grains VARGET
75 grain bullet 2.250” (magazine length)
August 12, 2012
According to Silhouette Ballistics software, when we plug in the measured velocity, this cold ammo will strike two inches lower at 600 yards than the “normal” temperature ammo.
Ammo under bag of ice in cooler (guessing to be around 35 degrees Fahrenheit)
Magazine loaded with ammo was placed under bag of ice about four hours before firing.



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NORMAL AMMO
24.2 grains VARGET
75 grain bullet 2.250” (magazine length)
August 12, 2012
Ammo from stool (approximately 75 degrees Fahrenheit)
Ambient temperature on day of test started around 70 degrees, and reached a peak of around 85 degrees at time of test. Temperature under cover of firing point was much cooler than temperature in sunny areas. Ammo remained in the shooting stool, in the shade at all times prior to the actual test.



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SCORCHING HOT AMMO
24.2 grains VARGET
75 grain bullet 2.250” (magazine length)
August 12, 2012
According to Silhouette Ballistics software, when we plug in the measured velocity, this super-heated ammo will strike four inches higher at 600 yards than the “normal” temperature ammo.
Ammo on black rubber on shooting mat on hood of car (approximately 110 degrees Fahrenheit)
This test is the “Rob M. Challenge.”
Rob has often pondered the effect of heat on ammo allowed to lie in the direct sun, on the black rubber area of a shooting mat, on a hot summer day. This is that test.
The car was driven with gusto for an hour, and parked in the direct sunlight on an 85-degree day.
The shooting mat was placed on the hood of the car.
The ammo was placed in direct sun on the black rubber area of the mat.
The ammo was allowed to “cook,” on the mat, on the hood of the car, for about a half-hour.
The very-hot-to-the-touch ammo was loaded into a magazine, and was immediately fired over the chronograph.



Allow me to again mention a related subject.
Effect of a round “cooked in the chamber.”
Rob and I already did extensive testing on the effect of allowing ammo to “cook” in the chamber. The purpose of that previous test was to address the belief held by many that it is necessary to remove a round from the chamber of the rifle in the case of a delay for wind-conditions, etc. when firing at 600 yards. The results of that testing were published perpetually at: http://www.usrifleteams.com/forums/index.php?showtopic=17858&view=findpost&p=166589

If you don’t want to bother with going back and reading all that, the somewhat shorter version is this:
1. A “cooked” round fired at normal 600-yard National Match Course rate of fire increases in temperature by a maximum of 16 degrees.
2. Even when using a known temperature-sensitive powder like IMR-4895, you cannot “cook” a round out of the 10-ring at 600 yards.
3. It takes 2.5 minutes for a “cooked” round to get as hot as it can get.
4. We used real instruments to measure the temperatures. We rigged a temperature probe inside an instrument round loaded with gunpowder.
5. We used Quickload/Quicktarget software to calculate the effect of elevated temperature on velocity in that April 24, 2012 report.




A remaining question to ponder is what is the additive effect of cooking the round on the black rubber of your mat, and then cooking it some more in the chamber. It appears that it is possible to cook a round at least 30 degrees over ambient temperature by placing it on a shooting mat in the sun. At worst, we might raise the temperature of that round an additional 16 degrees by letting it sit in the rifle chamber for a couple minutes. Based on the numbers I’ve studied, a temperature-change of 46 degrees should be good for an elevation shift about the height of the 600-yard X-ring (six inches).

By contrast, I wonder whether inserting an overheated sat-in-the-sun round into a warm barrel chamber might actually act as a heat-sink, and cause the temperature of the overheated round to stabilize, or diminish, as that overheated round sits in the chamber while the shooter makes doodles in his doodle-book and/or discusses the weather with the guy holding the fancy telescope. That test waits for another day.

 

[ferggie]

thanks to all

WEG Being that I am a Mechanical Engineer I appreciate you sharing your research with us. Great job and excellent write-up.

 

[JO JO]

I have had great results with 4064 and another to think about is TAC

 

[grubbylabs]

My 308 likes 4064 better. Varget does OK but 4064 is just plain better.

 

[mxjunky78]

Haven't tried Varget as 4064 performs so well for me in my 700 that I haven't bothered trying others.

 

[Walkalong]

IMR 4895 is hard to beat for overall .308 loading, although there are plenty of 4064 fans out there. I did not give Varget a thorough workout, but it just didn't wow like like I thought it might from all the fanfare. Keep in mind I do not shoot nearly the amount of rifle that some here do, so take that with a grain of salt. I am using RL15, but IMR 4895 and 4064 will shoot great as well. Too many people swear by them in .308 to think otherwise. I know IMR 4895 and RL15 will, and there are people I respect here who swear by 4064.

 

[J.R.W.]

I'm running 44gr of Varget with a 168gr (or 173gr pulled) Sierra Match King in my 20" Rem 700. It'll shoot cloverleafs at 100yds and hold 1.5" @ 200yds. I've yet to run it over a chrono.

 

[Dthunter]

What ever you can get is the right answer. If you can get both, allow your rifle to tell you which is best. Simple as that.

I have used both with great results.

I have had some AMAZING results over a huge temperature variation with Varget! From -35 degrees Celcius (-31F), to +35 (+95F), there was very little velocity variation. Maybe 50 fps.

This is critical if a shooter is shooting at long range as I like to do. Vertical dispersion was great!

I have never tested IMR4064 in those temp extremes yet.


The best advise that I can give is to develop loads with both powders (or more) if you can. This way it doesn't matter as much what is available. Cover your bases so to speak.