Temperature Sensitive Powders

Veener 7mm

Veener 7mm

Member
Rating - 100%
1   0   0
Location
Port Coquitlam, BC
I have heard that some powders (Alliant RL xx) are more sensitive to temperature change than say the IMR / H powders.

The reason I'm posting is because when I research a good starting load for my .300WM and my buddy's .300RUM, RL22 shows impressive velocities and gives tight groups with my 7mmRM. But, we live in the lower mainland where we test our loads in very mild temps and hunt where it gets pretty cold...much like a lot of other folks.

My assumption is that if a powder is temp sensitive and you work up a load in mild temps, when you go to hunt in a cold place that you would have slower velocities thus changing your POI. I am either chasing a ghost and the delta velocities are insignificant or this creates significant changes in velocity and needs to be considered when choosing a powder.

Anyone have any info or experience with this? Is there a chart or an article I can reference?

Any insight is greatly appreciated
 
Ive found RL-22 to be temperature sensitive. I noticed that when I locked a bolt on a rifle shooting in hot weather. The load had been tested in the spring with no real issues or pressure signs . Mind you I should of never been shooting that day....some lessons are learned the hard way.
 
Hodgdon's Extreme powders are designed to be more tolerant of high temperatures without causing dangerous pressures with normal loads, but from testing loads over the chronograph they suffer in the cold much like the others. On a brighter note, Hybrid 100V (made for Hodgdon by St Marks Powder) is claimed to be temperature stable to -40. Their test involved an airburst of a large volume of powder and taking the over pressure readings to make that determination. Whether or not that means there will be minimal loss of velocity at cold temperature when used in small arms ammunition is anyone's guess, but you can check out the test parameters on St Marks web site. I bought some and generally gained a little velocity across the board with it, but as yet I have not chronographed any in very cold temperatures.
 
Yep,

There is a HUGE difference in ANY powder I have tried(even Hodgdon Extreme).

From +15 deg -+20 deg a load developed in September will usually lose 100-150 fps when you try it in Nov., especially if the temperature is -20 deg C.

That is a given....I have not found a powder yet that can span 40 deg temp difference and maintain the same fps.
 
I have heard that H 1000, retumbo and H 4831 are fairly temp stable but I have yet to try them. I have found that RL 19 has given an extra 100 fps over the chronograph on hot days in the summer compared to cooler days in the the spring (270 win). If your not into long range shooting I think you will be OK with your POI as long as your pressures are safe.
 
Generally, I would say that the Reloder powders and H4350 and H4831 are quite temperature stable. IMR is very temp reactive. Don't know about H1000 but assume it is stable.
 
Thanks folks, some pretty good info here.

So the general concensus is the Big "H"s are more stable. We're going to end up doing a "gut check" before we go hunting anyways to determine the change in POI...if any with these powders. Also, I'll be checking my 7mm RL22 loads in a similar fashion.
 
Well, I worked up a load with some H4198 in august for my 45-70 GG and I just wanted to make sure it was still on the POI so I went last week to check and the POI dropped about 2 feet at 100 yards.
I was very surprised.
I expected it to drop a bit but not that much.
 
slow RL powders (22-25) and some slow IMR powders are at the top of temp velocity increase-decrease.

I find Hodgdon to be about the best, Varget, and (SC) short stick powders are pretty stable. Even the Ball powder is alot better now (H-380 & BL C2) are not as bad as they once were.

Most of my powder I use now is from H-extreme line
 
The writer John Barness,who lives in Montana,has written a fair bit about powder temperature sensistivety.He says Hodgdon Extreme,Ramshot and RL-15 are all fairly stable. The old ball powders were the worst. Others who have tested have found that the powder/cartridge combination affects temperature sensistivety.IMR-4064 in a 308 is good. I found RL-25 so sensistive in a 264 that I couldn't shoot three shot groups,the chamber heat would change the burning rate so much as to have huge increases in pressure/velocity.
The Swedes check POI during hunting season when using RL-22.
 
Veener 7mm said:
...My assumption is that if a powder is temp sensitive and you work up a load in mild temps, when you go to hunt in a cold place that you would have slower velocities thus changing your POI. I am either chasing a ghost and the delta velocities are insignificant or this creates significant changes in velocity and needs to be considered when choosing a powder...
Click to expand...

You are basically correct. But in my experience even the non-temp sensitive powders actually are affected to some degree by temperature. It can be dangerous is if you develop a max load in cold temp - it could be over-pressure in summer temps. The only way to find out about POI shifts is to try it.
 
I am a big user of Noma MRP, bought up a large quantity when it was readily available. It is indeed very temperature stable, unlike RL22. It still does drop some velocity in extreme cold, but I believe it is minimal. Here is what I found by actual shooting. My 270, with 130 grain bullets and 61 grains of MRP sighted in at 27ºC to dead on POA at 300 yards, was 1¾" low at 300 in -35ºC weather. My 308 Norma Mag with the 180 grain bullet only lost about 1" at 300 in the cold compared to the warm temps. Just to give a comparison, IMR 4831 dropped 4½" at 300 under the same conditions, and RL 22 was down almost exactly the same as the IMR powder. I would have chronographed these loads, but the 'graph did not work in the cold!! suffice to say, they were all maximum safe working loads at 27ºC. Regards, Eagleye.
 
phishroy said:
Well, I worked up a load with some H4198 in august for my 45-70 GG and I just wanted to make sure it was still on the POI so I went last week to check and the POI dropped about 2 feet at 100 yards.
I was very surprised.
I expected it to drop a bit but not that much.
Click to expand...

2 feet at 100 yds? That's not powder temp instability. You won't lose that much muzzle velocity with a temp drop. That's another issue like a bumped scope maybe.
 
If you don't use a magnum primer, it would be a good idea for winter ammo.

I used to have a job involving testimg ammo that had been cold soaked at -40 for 3 days. We wanted to make sure it allw ent BANG. A magnum primer helps.
 
jethunter said:
You are basically correct. But in my experience even the non-temp sensitive powders actually are affected to some degree by temperature. It can be dangerous is if you develop a max load in cold temp - it could be over-pressure in summer temps. The only way to find out about POI shifts is to try it.
Click to expand...

I used IMR4820 for my 30-06. I made a wack of them in Dec. I took them out to check the sighting of my rifle the next summer and was greeted with a recoil that was the equivelent of a slap to the face and a kick to the groin at the exact time. I learned after that to make loads in the summer and test them in the winter, less chance of doing dammage to self or toy! I also learned that IMR 44850 or 4831 is better for the 30-06
 
You must log in or register to reply here.
Back
Top Bottom