I am reloading for a trip to Africa on Saturday and have a load using 73 grains of IMR-4350 in my .338 WM that gives me .443" groups, but opens up to 1.125" with 74 grains, and 1.5" with 75 grains. The 75 grains load also gives me sticky bolt lift. All this is with a temperature of 9 degrees celsius. Since Namibia will be around 30 degrees clesius during the day, I am concerned about pressure fluctuations due to the temperature change, and would like to load down a bit to duplicate the .443" load at that temperature. I was think of dropping my load to 72 grains, but I'm not sure if that's enough, or even if it's necessary. Can anyone advise? I am under the impression that IMR-4350 is one of the worst powders for temperature sensitivity, and want the most accurate load possible, especailly since this rifle will most shoot smaller African critters and varmints at night under lights.



Thanks!

Unless you are loading past book max, you will not have a problem, or at least I never have. I think that's mostly bunk, and when it happens it is the result of poor handloading practices for the most part...A couple of grains below max makes little practical difference in anything as far as trajectory and killing power goes...

Use at your own risk....

If you REALLY want to see how your loads will perform at higher temperature, shoot several rounds to get your barrel good and hot, then chamber one and let it sit. When all is good and warmed up, let 'er rip and see where it goes. Repeat as necessary, watch carefully for pressure, etc. etc. etc.

Well, for starters, you did not tell us what bullet you are loading!!!!

But if that darned load of 73 grains of IMR 4350 shoots so good and has not blown up your rifle, those must be pretty light bullets, as in 200 grains or maybe 210's.

If the 73 grain load shoots so good, it seems like the best choice.

If the 75 grain loads have been safe, then a load of 73 grains should be safe at darned near any temperature!

Based on the information provided, I would go with 73 grains and call it good.

R F

If you are shooting anything other than a 200-210 grain bullet with 73-75gr bullet I think you need to back the load down to 70-71grs. 71grs has been my max load for 225s in 3 different 338 Win Mags. I have load tested this in hot weather Up to 42deg C (over 100deg F).........DJ

What bullet are you shooting and is it touching the lands?

When something big and fangy is about to eat your ass, it is no time to be dicking around with a sticky bolt. Perhaps they could put on your tombstone: But his bullets were going really, really fast."
Just kidding. Listen to Ray.

Give Reloader powder a try, they give excellent results in large capacity cases. Rel- 19, 22, 25, should produce excellent accuracy and are more tempurature tolerant. It is always best to work up your load at the tempuratures your going to be hunting. One thing is certain it won't be snowing in Africa and the heat is your number one concern. You would be making a big mistake considering any load that produces hard bolt lift in any actual hunting scenario.

I would concentrate on producing the most accurate smooth working bolt lift load I could get. Bullet placement, along with proper bullet selection is the key to success in Africa. Accuracy first and velocity will take care of itself. It is certain not one of the animals you harvest will ask you how fast the bullet was traveling when it struck them. It is not likely you will be taking any long range shots. Most should be under 200 yards and probably average 100 or less yards using long shooting sticks.

Sheldon -

With the older powders velocity/pressure is clearly a function of temperature. I don't have my IMR data at hand, but with AA 2460, 2230 and 2015 as an example it's clearly the case (and if memory serves me the I4350 data wasn't that much different). (Some powders are much less sensitive - vv and hodgdon extreme.) We were testing for this a couple of years ago: in the context of a 444 marlin, 240gr jsp, where the chrono/ambient was in the 66-72degF range, but the reloads were heat/cold soaked for 30mins before shooting:

aa2460 50gr: 112F 1807fps, 66F 1747, 32F 1711
aa2230 55gr: 116F 2129fps, 66F 2117, 32F 2075
aa2015 52gr: 116F 2191fps, 72F 2106, 32F 2010

The generated velocities are the average of 10 shots.

hope that helps, and do shoot straight,
greg
www.gmdr.com

I ran a test on Hodgdon "extreme line of powders" for a college science experiment and found that on average of the powders tested, when the rounds match the ambient temperature, there was a 3 FPS difference in velocity per degree from 40 - 80 degrees F. The hotter the ambient temperature got after 80 degrees, the greater the difference. The colder the ambient temperature got under 30 degrees, the less difference in velocity change between the temperatures.



For my calculations I say there is a 30 FPS change in velocity per every 10 degrees of temperature change. I've been using this rule for the last 3 years in load development and it hasn't dissapointed me yet. The biggest factor is finding from the powder manufacturers what temperature was used for their listed data. I know Hodgdon uses 70 degrees F for instance for all of their listed data.



I have a book that lists the temperature change rate for IMR powder, but don't have it with me at this time, though I will come back and post if you want me to.



My suggestions: You need to back down your grain charge. If your load is pushing max velocity, or exceeding the max in the colder temps it will be dangerous in the hotter temps, especially the temps common in Africa. Besides, when we load our rounds to near max we are almost always exceeding the velocities of factory ammo.

I get about 40-60 more fps in the summer than in the winter here in Alaska. It's usually around 0-20F. when I work on most of my load data, and 50-70F. in the summer.
Oh yeah it's a 375 imp with IMR-4350 no where near max.