H4895 Temp Changes

[Forum Boss]

I don't know how the OP placed his ammo on the bench.

However you have to look at the temperature of the cases, not just the air temp!

Some years ago I was shooting a match, and a couple shots went WAY high. Powder was Varget. The ammo had been sitting IN THE BRIGHT SUN in a MTM case, top open. (Stupid yes I know... but this made for a very illuminating discovery.)

The ambient temp was only about 80 degrees. But the cartridges themselves were actually hot to the touch -- so over 120 deg F my guess.

I withdrew from the match and went to another range area to chron the ammo -- I kept it out in the hot sun just as before. The chron readings were 70-80 fps higher than normal.

I took the remaining ammo, and shot it the next week with ammo kept covered in shade at about 75-80 degrees ambient. Velocity was completely normal.

Also, you have to be mindful of the temperature of the chamber, which can transfer heat to the cartridges pretty quickly

 

[Ned Ludd]

I don't know how the OP placed his ammo on the bench.

However you have to look at the temperature of the cases, not just the air temp!

Some years ago I was shooting a match, and a couple shots went WAY high. Powder was Varget. The ammo had been sitting IN THE BRIGHT SUN in a MTM case, top open. (Stupid yes I know... but this made for a very illuminating discovery.)

The ambient temp was only about 80 degrees. But the cartridges themselves were actually hot to the touch -- so over 120 deg F my guess.

I withdrew from the match and went to another range area to chron the ammo -- I kept it out in the hot sun just as before. The chron readings were 70-80 fps higher than normal.

I took the remaining ammo, and shot it the next week with ammo kept covered in shade at about 75-80 degrees ambient. Velocity was completely normal.

Also, you have to be mindful of the temperature of the chamber, which can transfer heat to the cartridges pretty quickly

^^^This. Combustion is a chemical reaction...ANYTHING that changes the temperature of the loaded ammo, including case, powder, primers, etc., the action, or the initial region of the barrel where a good portion of the reaction takes place has the potential to affect velocity.

 

[Immike]

I’ve had trouble in the past with ammunition too hot from the oven effects of ammo boxes exposed to sunlight. Have gone as far as putting it in a cooler over ice that’s underneath a towel. It works very well actually...

 

[barefooter56]

No powder known to man is completely insensitive to temperature change. I use a lot of H4895 in .223/.308 and your "temp change" results are much, much higher than anything I've ever seen, making me wonder what else might have been a factor.

Barrel heat is what I had going when I noticed the recoil getting stiffer along with the blot lift with H-4985 AND MY .308 WIN during a string fire test. Even leaving the cartridge on the feed ramp with the bolt open until the target was acquired. It was also a hot humid day. And on those type of days the rifle just stays hot for a long time.

 

[Depart123]

Ever wonder how Hodgdon defines "temp insensitivity"? The extreme powders will light at extremely cold temps almost as well as at moderate temps. This gives them a vary small variation between say 20 degrees and 70 degrees, something on the order of 0.3 - 0.5 fps per degree of ambient temperature.

Above 80 degrees they are only a little less vulnerable to heat as any other powder. This allows Hodgdon to average the change per degree over the whole range tested and claim "temp insensitivity". Of course, when they do thier testing, the powder tested has the optimal amount of moisture content. Store your powder in the garage in Phoenix, and you will find that the burn rate and temp sensitivity has changed.

So, they aren't lying...it just doesn't mean what you think it means.

 

[alinwa]

....... Then you come along and imply in your typical condescending manner that other people don't really ever test things or can't possibly know as much about it as you, while at the same time .........

If you want to believe you're the only one that knows anything about the topic, go right ahead. ............. That's what this is really about isn't it?

Nothing could be further from the truth.

Sorry to have entered your room, now I know, I won't again

 

[Sheldon N]

I've done a simple temp test with H4895 in the 6BRA. It was a cold day outside, about 40 degrees. I left 5 rounds outside until they fully cooled to ambient temperature. I took another 5 rounds and sat in the car with the engine running and the heater on and held the rounds in the hot air of the heater vent until they were quite warm. Probably 85-90 degrees. Warmed up the magazine too so it would stay warm when I jumped out of the car and loaded the gun.

6BRA 30.8gr H4895 Sierra 110MK CCI 450 26" barrel (as an FYI this is a slow lot of H4895 compared to others)

40 degrees = 2850 fps average
85-90 degrees = 2875 fps average

 

[BT1]

I've done a simple temp test with H4895 in the 6BRA. It was a cold day outside, about 40 degrees. I left 5 rounds outside until they fully cooled to ambient temperature. I took another 5 rounds and sat in the car with the engine running and the heater on and held the rounds in the hot air of the heater vent until they were quite warm. Probably 85-90 degrees. Warmed up the magazine too so it would stay warm when I jumped out of the car and loaded the gun.

6BRA 30.8gr H4895 Sierra 110MK CCI 450 26" barrel (as an FYI this is a slow lot of H4895 compared to others)

40 degrees = 2850 fps average
85-90 degrees = 2875 fps average

Thanks for the effort to actually test something. Some just like to opine about what someone else said or did or did not do.
Steve

 

[JohnMill]

No changes to anything. Did not clean the gun.

Hey Terry,
You done pretty well for all that. Do you think the elevation at Trout Run Mountain might have had anything to do with it. I know ther is a difference between there and Sun Prairie.
JohnMill

 

[Terry]

Hey Terry,
You done pretty well for all that. Do you think the elevation at Trout Run Mountain might have had anything to do with it. I know ther is a difference between there and Sun Prairie.
JohnMill

John

Thanks!

I have not seen a change in mussel velocity due to elevation.

Others:
All ammo was kept in the shade, and only chambered when firing.

Thanks to all!

 

[JamesnTN]

I’ll jump in on this before it cools down and test H4895 from 70-90* and see if there’s a big change. The ammo will be left out in the shade so as the temp rises so will the ammo. I’ll shoot a string of 5 shots each at 70,80,and 90* and will report back on the results.

 

[JohnMill]

I was testing and shot 5 four shot groups in a row to see if the they moved and group size would change. 31.0 was 2977 for 3 groups and it went up to 2982 in group 4 and 5. I would guess the lot # has a velocity change more than the heat form the barrel. This barrel took almost 150 rounds before the velocity was stable. ..... jim

Hey Jim, Is the speed then stable just for that day or is it stable for an extended period. In reading this group (6BR, improved etc) i get the idea that bullet speed changes throughout the barrel life but I have no idea at what rate or if.

 

[johara1]

Hey Jim, Is the speed then stable just for that day or is it stable for an extended period. In reading this group (6BR, improved etc) i get the idea that bullet speed changes throughout the barrel life but I have no idea at what rate or if.

Pretty much, that speed was stable, I was showing what it did over 20 shots starting with a clean barrel after 1 fouler and how it held fo 3 groups but as it heated and fouled it did gain speed but 5 fps. I could live with..... jim