IMR Powders

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I`m fairly new to this reloading thing so this question may sound stupid to people in the know so I apoligize in advance . With IMR powders I`m told they are temp. sensitive does that mean if you work up a load its no good in summer?Is it that it works only in a set range ie 16-25 C ? Or it works best above a certain temp. ie 20 deg C ? It is just a broad term that does not seem to be explained .
 
All powders are temperature sensitive, but to varying degrees. Hodgdon's "Extreme" powders for example claim to work consistently across a large range of temperatures.

Generally the warmer the ambient temperature, the higher the pressure (and higher the velocity), so develop your loads and zero your rifle in the temperature you expect to shoot it in when it counts.
 
When you produce a handload, and the temperature is extremely cold, your velocity and pressure will be reduced. Therefore, more powder can be used and the load will be ok.If you use that same load in extremely hot temperatures, the pressure curve rises, velocity increases, and pressure can and will increase dramatically.If you stay within the guidelines of a good reloading manual,you should have no problems whatsoever. Bullet seating depth can cause pressures to skyrocket also.Seat your bullet so that it does not engage the lands when chambered. That way, it gets a little jump and some speed before it hits the rifling. If it is touching, the pressure has to rise very sharply to get it to move. All powders will give a variation if loaded and fired at 80 or 90 degrees, and then used at - 20 or -30. A hot - 30 degree load may be way too hot at 80 above. Hope that this helps. By the way, what are you loading for? Perhaps I can help.
 
The load I`m shooting for is for the 243 win. At present I have had pretty good accuracy with 37.7 of varget behind 68 gr brawand bullets. By some sort of freak accident my best group of 5 is .200 " . That is the group on the left with a dime.
 
All the powders are sensetive to a point. Not using a powder because of your fear of it being overly sensetive could be a mistake since it might be the one the rifle likes best. Adjust your loads accordingly and try different powders in your rifles. A very good powder for the 243 is IMR4350 with the 85-100 grain bullets.
bigbull
 
bigbull said:
A very good powder for the 243 is IMR4350 with the 85-100 grain bullets.

Agreed. My (old) Savage 243 likes 40gr of IMR4350 and a 100gr BTSP (Hornady or Sierra - both shoot the same). It is not a "hot" load, but is very accurate and consistent. I never saw a difference from Summer (<20C) to Winter (-10 to -15C). It has taken a few whitetails and many QCI blacktails.
 
I reload for about 14 different rifle calibers and have been shooting the same " acurate " loads for many years....All loads that were close to the "edge" were always developed and fired in summer temperatures and if found to be safe and accurate could and were shot year round....Chronographing the loads later in our winter showed no real measureable differences nor did accuracy change..

We do not get the low temps that the rest of you get, but have a friend in Sask. that reloads, and states his velocities differ a bit but if it was an accurate load at 20 + degrees it was still good at well below freezing during their hunting season....

Most of my loads are over todays Reloading Manuals max as many came from the old P.O. Ackley reloading books from the 1960's....however they are safe in my rifles..

If your rifle shoots well with a particular load in summer and does just as well in winter ,a few dozen feet per second lost to the cold is of no consequence
on any game you shoot.....If you live in the Arctic no doubt a few more grains of powder and a magnum primer would get you back to book velocities if it was safely built up to and you feel you need it.....


hs45/70................your mileage may vary
 
i use imr4064 for 87gr vmax and imr4350 for 95gr sst's. my groups open from .3 in summer to .5 in winter. but i can't say its the powders fault. the same happens with my 204 which burns only Hogdon extreme powders.

my observation is given the conditions i don't notice much difference.

hs4570 seems to have scientific info to support that.

my testing temperature range was only from +30 to -28 C
 
Mr brother reloads using Hogdon's Varget, part of their "Extreme" powder line. We both hunt with them and they are very consistent in terms of velocity and performance regardless if its a late season Moose hunt with minus 20 degree weather or punching paper in the summer when its 25 degrees out.
 
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