I switched from IMR powder, specifically to H4350 and H4831SC for use in my 257 Roberts, because those powders are said to be less affected by temperature extremes than the IMR products.

I don't seem to be getting nearly the same accuracy with the H powders as I did with IMR, and I wonder if the advertised lack of temperature sensitivity makes a lot of difference. I don't usually take my gun out when the weather is nasty and in the 20s, nor do I do much when the thermometer is above 90 degrees.

So, should I shoot up the powder I have, and go back to the old standby, IMR? What have been your experiences, or doesn't it make no nevermind? Thanks.

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I wonder if the advertised lack of temperature sensitivity makes a lot of difference

I know many swear by it being an issue. Probably 75%+ of my loads are RL powders. Which many will say are very temp sensitive. I'm a very firm believer of if it isn't broke don't fix it. You had good accuracy I gather hadn't had temp issues so why change? Unless you had a huge amount of H powder to deal with I would simply save it for another project and return to what worked.

Many years ago, I tried H-4350 in place of IMR-4350 in several cartridges. I found that the IMR gave better accuracy in my rifles. Similar results with the 4895 versions. Of course, this was before "temperature sensitivity" became a big deal. (before they became "Extreme")

The only Hodgdon powder that I use is Varget.
It is my powder of choice for the 257 Roberts.
In this particular rifle Varget out performed
any of the IMR or RL on my shelf.
GOOD LUCK and GOOD SHOOTING!!!

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I wonder if the advertised lack of temperature sensitivity makes a lot of difference.

IMO temp sensitivity is way over worked.

I might agree with powders used for summertime varminting where many of us have noticed increases in pressure with our varmint loads.

However it needs to be understood that many of load our varmint loads quite hot in the first place....(we're not too smart that way )

On the other extreme.....if the weather goes much below -20 F.....I won't go out anyway!

If you've substituted these powders weight for weight, then that may be where your problem lies.

Neither powder duplicates the burning rate of the same NUMBERED powder in the other line. H4831 is particularly slower than IMR-4831. In other words, with the same weight of H4831 both your velocities and pressures are going to be somewhat lower than with IMR-4831.

If you adjust the powder to a charge that is appropriate to it you may find your accuracy restored. Or not. But there is nothing inherently "more accurate" about the IMR line than the H line of powders.

BTW: "Temperature insensitivity" is a term that was coined by the Hodgdon marketing people, not by the ballisticians or chemists. That should provide some indication of the intrinsic value of the term.

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"Temperature insensitivity" is a term that was coined by the Hodgdon marketing people, not by the ballisticians or chemists. That should provide some indication of the intrinsic value of the term.

Great post....love it!

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.. for use in my 257 Roberts,... What have been your experiences, or doesn't it make no nevermind?

It may or may not matter in your .257. Whatever, it sure isn't something anyone else can acurately predict for you.

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Originally posted by Stonecreek:
If you've substituted these powders weight for weight, then that may be where your problem lies.

Neither powder duplicates the burning rate of the same NUMBERED powder in the other line.

BTW: "Temperature insensitivity" is a term that was coined by the Hodgdon marketing people, not by the ballisticians or chemists. That should provide some indication of the intrinsic value of the term.

Stoney;
Ah-hah! The same value as "NEW and IMPROVED", no doubt.

I did start over with data published in reliable manuals (not the 'net) to begin my evaluation of the H powders. That's the only way to fly!

For 35 years my Ruger .257 Tang safe varmint shot sub MOA with the three 4350s, two 4831s, DP85 and DP86. The rifle still digests these powders quite nicely but not as good after 38 years and perhaps maybe 6000 rounds. Powder selection in this rifle never seem to matter much. roger