IMR 4895 Temp Stability in the 308

[918v]

Hi

I found three pounds in my garage I forgot I had. I think it's 20 years old or older, metal cans. I worked up a load in Winchester brass: 41.6-42.4grs under a 175SMK. The 41.6 and 42.4 charge weights produced .7" groups, but what made my day was that the 41.8, 42.0, and 42.2gr charge weights all printed in the same spot and produced the same .4" group size. So my load is going to be 42grs.

Here's the question:

If I have an awesome load, one where a .5gr powder charge weight variance does not affect POI, and I weigh out all my charges to exactly 42 grains, just how much will temperature swings affect long range accuracy?

I also worked up a load using Varget, but it does not give me the same amount of cushion. I'm thinking what good is temperature stability if the load is less consistent. Does anyone gave an IMR 4895 temperature swing data for the 308?

 

[expiper]

Hi "V"...you have found the sweet spot ,,,as you can see the powder doesnt have to be weighed to the millionth of a grain to be good,,!!!,,,people were using 4895 in 06' and 08's before most shooters were alive today,,,,enjoy your new found stash ,,,,I wish you had a wheelbarrow full of it,,,,Roger

 

[ShootDots]

I used to use IMR 4895 in a 22-250 and a 220 Swift. My experience tells me it is "fairly temp stable" for not being an extreme powder. With the window you have, I would not worry about a thing.. I have found that IMR 4895, IMR 4320, IMR 4007 and IMR 7828 appear to be pretty temp stable. I have had problems with some of the other IMR powders I have used but with a nice wide window like you have, I have never had a problem.. Even if you used Varget or other "extreme" powders, and run them to the ragged edge of "safe" pressure, temperature swings can take you out of your accuracy node.. I try always to have as large of a window as possible, to keep from going out of my node..

 

[Syncrowave]

I never actually checked whether POI changed with Δt but IMR4895 was always my go-to powder for light varmint rounds in my 270 Win (Speer 100 gr HP over 48.5 gr IMR4895 with bullet jammed) and it always seemed to work like a charm, whether it was winter or summer!

Once I found that load, I never used anything else for varmints/targets in 270 Win.

 

[Mr. Ten-X]

just how much will temperature swings affect long range accuracy?

Accuracy? Not exactly certain.

Elevation is another matter. The Army used a canister-grade IMR4895 for the M852 Match/sniper ammo. That required a 1MOA elevation change for every 20 degree change in temperature from your established zero.

 

[Shynloco]

Hi

I found three pounds in my garage I forgot I had. I think it's 20 years old or older, metal cans. I worked up a load in Winchester brass: 41.6-42.4grs under a 175SMK. The 41.6 and 42.4 charge weights produced .7" groups, but what made my day was that the 41.8, 42.0, and 42.2gr charge weights all printed in the same spot and produced the same .4" group size. So my load is going to be 42grs.

Here's the question:

If I have an awesome load, one where a .5gr powder charge weight variance does not affect POI, and I weigh out all my charges to exactly 42 grains, just how much will temperature swings affect long range accuracy?

I also worked up a load using Varget, but it does not give me the same amount of cushion. I'm thinking what good is temperature stability if the load is less consistent. Does anyone gave an IMR 4895 temperature swing data for the 308?

I can't help you with "temperature data" per se, but will mention that I use IMR 4895, RE 15 and Varget, all right at or around 42 grs (gotta test in you particular rifle) in my .308 that I shoot at 100 yds using 168 gr HPBT, both Sierra's and Noslers.. I live in the high desert area of So California and shoot my rifle both in cooler temps (this will be a joke to most folks) low 40's all the way up into the mid 90's in summer. What I found of the three powders I mentioned, Varget gives me the greatest variance in accuracy when temp go over 90 degrees. I've not seen much of a deviation at all with either IMR 4895 or RE15 unlike the Varget. Some say Varget isn't temp sensitive...my response, bet me!

P.S. Try not to do the 918 thing, especially south of the border.

 

[918v]

I read one guy's test where he showed Varget pressure to increase with increasing barrel temperature.

Maybe it's insensitive to ambient temperature but it is sensitive to other factors. If you jump out of an air conditioned vehicle into a 100 degree environment, Varget may be insensitive. But if you allow your equipment to acclimate, Varget may be no better than the classic powders.

The military gas gone with IMR 4064 in their new sniper round. They claim a 20FPS variance over 100 degrees. But what was the test protocol?

 

[gaboon]

I purposely took 75 degrees ammo and some 35 degrees ammo and shot it. I waited 20min between groups the poi didn't change at 200yds. I was using IMR 4064 in my 308. I have been using IMR 4895 till the great shortages. The same load works for me using both powders. The 4895 did not change that much in the hot or cold maybe a click or two.

 

[K22]

First of all, IMR 4895 is a great powder for the 308. It's worked very well for me with 125 and 150 grain bullets.

I do most of my shooting with the 308 in temperatures of 40 degree and lower in preparation for big game hunting seasons so I can't offer much insight on temperature changes for this specific cartridge / powder combo.

However, I've used this powder in the 223 over a wide range of temperatures and I've noticed a change in elevation of approximately 1/2 to 1" from summer months (90's) to winter (30's). I'm not an expert on this but this change may be due to air density changes not so much due any temperature intolerance for this powder. The reason I say this is I've a similiar change using Varget in the 223 which is suppose to be one of those extreme powders and very temperature tolerant.

 

[1shot]

I keep reading posts such as these but with the flavor of the week. Then I go back to my IMR-4895. My shooting partner moved from Ohio to Colarado and when we decide to look at 2-4 different powders, we both try a couple each and exchange information in regards to ES, velocity, pressure,etc. We have identical barrels, by the same maker,same length and rate of twist, chambered with the same reamer by the same gun plumber. We both shoot the Berger 185 OTM or Juggernaut depending on the part #. With all that said, IMR-4895 is our go to load. We do vary a little on charge weight but we shoot different receivers. FWIW, it is a very stable powder that doesn't offer any surprises at the wrong time.
I hope this helps,
Lloyd