Do Hodgdon Extreme powder perform the same in cold as warm or hot temperatures? A load that shot .5 or less @100yds in 50-60 degree weather with Benchmark shot about 2" pattern in 18 degree temps. The load was .223 50 VLC, Benchmark, Win cases and 7 1/2 primers. DO i need a mag primer for colder weather? The first group was strung out vertical. The gun is bedded. Whats the best cold weather combo for the .223? Thanks, H.H.

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Originally posted by Horn-Harvester:
Do Hodgdon Extreme powder perform the same in cold as warm or hot temperatures?

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Well, they're supposed to. That's the basic idea behind the Extreme line.

What you're seeing could also be from the rifle physically shifting with the temp drop. Is the barrel floated? What kind of stock do you have?

RSY

The short answer to your first question is, sometimes.

Hodgdon powders advertise temperature independence, but do not deliver it in all cases. For instance, Varget is superbly temperature independent in the 308. It is worse than ball powder in the 223.

It seems that there is a second factor, such as case size, or percent fill, that is part of the equation.

The original claim of magnum primers was reliable ignition of slow burning stick powders in very cold weather. Don't know of it is true, or what it means in your case, but that was the claim.

How does this work? I haven't studied much chemistry but I do know that reaction time varies with temperature. I thought before reading this post that the message from Hogdon was that variance somehow is minimised at extreme temperatures. (i.e. increased optimal temperature span or something).

Olli, I'm not quite sure how it all works. The following is just a partial answer.

SAAMI does not control barrel temperature in testing pressures. They go to ridiculous lengths to control ammunition temperature. Ambient pressure is probably not important at all, except for its influence on ammunition and barrel temperature.

Barrel temperature is about 3X as important as ammo temperature.

If you leave a cartridge in the chamber for 5-10 minutes, the ammunition temperature will become the barrel temperature.

So, when you ask about the effect of temperature on MV or pressure, you have to ask, the temperature of what??

It's only a guess at this point, but it seems that the temperature of the primer may be the actual critical factor.

Hodgdon's advertising claims greatly exaggerate the temperature independence of their powder. In fact, I would say that their advertising claims are in the realm of false advertising. It is NOT true that their Extreme powders give full temperature independence in all cartridges.

In my 30-06, H4350 gives good temperature independence. When I had a 308, 46 grains of Varget gave almost perfect temperature independence.

In my 223, Varget gives very poor temperature independence. I did this test before I understood the effect of barrel temperature, and simply fired the rounds in 25 degree weather, and in 80 degree weather. The change due to temperature is larger than that of "military" 223 ammunition available across the counter.

In my 7.62x54R, H4350 has almost exactly the same temperature response as IMR 4350. This cartridge has a bit more case capacity than the 308, and a little less than the 30-06.

More info in the Pressure Factors article at http://www.shootingsoftware.com/tech.htm

The temperature of the ammunition makes the most difference. If you let the ammunition temperature match the ambient temperature, then for every 1 degree change in ambient temperature there will be an approximate 3 fps change in muzzle velocity for the Hodgdon extreme line of powders H4831, Varget, and H4895. (30 fps per 10 degree change). If the ammunition temperature is hotter than the ambient temperature, then there is less change in velocity. I found shooting ammunition with a temperature of 70 degrees in 30-degree weather yielded only a .8 fps change per degree.

For example, you are riding around in a truck with the heater giving a truck cab temperature of 70-75 degrees in 30-degree weather. The ammunition temperature is around 70 degrees. If you fire from the truck, or shortly after exiting the truck, then the velocity change will not be significant.

For example: You keep your extra ammunition close to your body while out hunting in 30-degree weather. If you were to fire this ammunition, the bullet would travel faster than the ammunition sitting in the magazine of the gun that matched the outside temperature.

I also found that muzzle velocities change less, or stabilize, as the temperature drops with the most notable change after the 30-degree mark. This is opposite of the hot weather. Muzzle velocities continue to increase with ambient temperature increase, with the most notable changes occurring after the 70-degree mark. More clearly, moving from 30 degrees to 10 degrees will have significantly less velcoity change than moving from 70 to 90 degrees. (At those higher outside temperatures, the velocity changer can be as high as 6 fps per degree).

My advice is to zero your hunting gun to the conditions in which your hunt. For traditional hunting, you should zero with ammunition matching the weather. By doing this, you mimic the most practical and realistic hunting condition, where both your gun and ammunition will be exposed to the same ambient temperature during the hunt. If you hunt from a heated enclosure, where the temperature inside is hotter than the outside weather, then zero per those conditions.

Also, the reduction in sensitivity is related to muzzle velocity. It is a reduction in sensitivity. Not an absolute stability. If the accuracy nodes are 300 fps apart, and we are changing 3 fps per degree, you can still easily drift out of your "node" with a 50 degree shift.

Secondly, I am not a vibration expert, but it would seem plausible that a barrel vibrates differently at low temperatures than at higher temperatures. Further complicating things. FWIW, Dutch.

I have been doing quite a bit of testing this winter on many of my reloads. In a 25-284 the velocity with 100 gr bullets and SC4831 has been constant at 3300 fps regardless of temp from 90 deg to 10 degrees. In a 338 WM and IMR4350 I loose 100 fps with 210 gr NP and same temp spread. RL 19 is the worst - loose 150 fps with 225 gr hornady. RL 22 in a 270 with 130 and 160 gr NP's loose 100 plus fps. RL22 in a 7 mm RM and 175 HSP looses 100 fps from 2920 to 2820 fps. MagPro with 139 HSST in the 7mm lost only 40 fps from 3300 to 3260. My focus in the future will to use only temperature resistant powders. I will be switching to H4350 for both my 243 and 338WM. RL22 is so accurate but I will use SC4831 or MagPro instead. By the way the guns were taken from the inside of the truck during the cold testing and during testing got progressively colder. The ammunition was stored in the unheated garage so it was pretty well cold soaked. Hope this helps

Perhaps the firing pin was dragging on your 223? Try it again after cleaning it and the bolt. Sure is plenty of cold weather ahead.

The general feeling is that magnum problems are good in cold weather.

The report by 2manyguns is the first I have read with specific data. What primers did you use?

I have seen none from Hogdon. If they have some data I hope someone can link to it.

WLR's in the 25-284, 270 and CCI250 or WLRM in the 338 and 7mm. Also in a 222 BLC2 with 50 gr NBT looks pretty good at 3260 fps on a 10 deg day - but I have not tried it at elevated temperatures - yet.

I loaded 20 rounds last night with 26grn of Varget, 69 Sierra HPBT match in new Win cases. Ten of them i used CCI 450 mag primers and the other 10 Rem 71/2. Today it was 12 degrees out. I shot them slow so not to heat the barrel and the bullets were out side. I didnt run them over my chrony but both 10 shot groups were about .75 with a flier or two. I had a stiff 60 degree wind. The mag group was slightly tighter. Thanks to all that replied, H.H.

I am not sure about the temp changes and how well it works yet. I am shooting in Florida and I was loading IMR 4350 in my 300 SAUM and getting good groups. I switched to H4350 EXT because of the shorter grain not taking up so much space in the case. The 300SAUM does not have the volume of the WSM. What I was pleased to find is that my okay groups went to perfect groups. I loaded 61.5 grains with a 180 BARNES TSX and Winchester Mag primers. A dime covered 5 shots at a hundred. I am not changing anything after that. I will check the temp performace in a month or so.