IMR4350 Temperature Sensitivity

[Tony k]

Today I tested some IMR4350 with 130 grain Sierra Game Kings in my Savage 111 in 270win.

Best groups were 54, and 54.6 grains of powder, which is near max listed in my Sierra Manual (55 is shown as max)

Temperature at the range while I was testing was about freezing. I didn't get any over pressure signs at these temps, even at 55 grains. Yes, there was some primer flatening, but no cratering, blow-by, or bolt face marks on the headstamps.

My understanding is that IMR4350 is somewhat temperature sensitive. What are the chances that I'll experience over-pressure with the 54.6 grain load when the temp is in the 80s or 90s?

Thanks

 

[jwrowland77]

On the loads that I have for my 7mm RM for hunting, I tested originally in 100 degree weather. Then I tested again in 30 degree weather due to hearing that the powder was temp sensitive. I saw practically 0 change in performance and MV. There was only a 6fps difference between the hot and cold weather, and that could be simply the way I held my rifle that day. I never saw a difference in my rifle or load.

 

[rcmodel]

IMO: If you are loading so close to the bleeding edge with IMR (Improved Military Rifle) powder that you have to worry about it?

You are loading too close to the bleeding edge in any kind of weather.

rc

 

[243winxb]

http://www.hodgdon.com/smokeless/extreme/index.php#top Hodgdon should know. They sell both. I have never had a problem with IMR4350, but never really heat/cold tested it. Having shot both H & IMR in 243, i wll buy the H next time i see it.

 

[jwrowland77]

That's a pretty large extreme they used in testing. How many of us actually shoot in a difference of 125 degrees in a given year? Probably not many.

 

[jmr40]

IMR-4350 can be expected to change about 1-2 fps for each degree temperature changes. Unless used in extreme conditions, hot or cold it will rarely be a problem.

I've used both IMR4350 and H4350 in my 30-06. Accuracy and velocity with both powders is almost exactly the same, with a very slight edge in speed going to the IMR version. Not enough to worry about. I've settled on H4350 simply because it is far less sensitive to temperatures. But it isn't something I worry a lot about. If the IMR4350 proved to be considerably more accurate then it is what I'd use. As it is there isn't any accuracy difference so I figure why not use the powder that is less sensitive.

 

[Tony k]

IMO: If you are loading so close to the bleeding edge with IMR (Improved Military Rifle) powder that you have to worry about it?

You are loading too close to the bleeding edge in any kind of weather.

Are you saying that you consider 1 grain and .4 grain below published max, with no over pressure signs, to be the "bleeding edge" in this case? And why are you pointing out that IMR stands for "Improved Military Rifle"?. I'm not trying to be snotty; I'm just not exactly sure what you mean.

I don't necessarily see it as the bleeding edge, but that could be the foolhardiness of someone who's only been reloading for a little over two years .

This is intended as primarily a hunting load in temps ranging from the 80s in august, down to the teens in November. If it proves to be as accurate as it seems to be so far, I also want to use it in local matches.

 

[rcmodel]

I wasn't trying to be snotty either.
Sorry if it came across that way in print.

I was pointing out the meaning of IMR, because that is the initials of the full name of it when various burn rates were developed years ago for military use.
In all kinds of hot & cold weather, world-wide.

I took from your OP that you had concerns about being close to a hot load in 'your rifle', not the book, at summer temperature?
Guess not.

My mistake, again.

Sorry!

rc

 

[Tony k]

IMR-4350 can be expected to change about 1-2 fps for each degree temperature changes. Unless used in extreme conditions, hot or cold it will rarely be a problem.

I've used both IMR4350 and H4350 in my 30-06. Accuracy and velocity with both powders is almost exactly the same, with a very slight edge in speed going to the IMR version. Not enough to worry about. I've settled on H4350 simply because it is far less sensitive to temperatures. But it isn't something I worry a lot about. If the IMR4350 proved to be considerably more accurate then it is what I'd use. As it is there isn't any accuracy difference so I figure why not use the powder that is less sensitive.

I can deal with 100fps difference between winter and summer shooting I guess, but that seems like it could also come with significant pressure differences.

Amazingly, I actually had a choice between H and IMR when I bought this. I knew they were both supposed to be good in .270, so I just randomly chose IMR. Darn it, it didn't even cross my mind that temperature sensitivity was one of the differences. I ASSUMED that IMR4350 was temperature insensitive because it's not a ball powder. I still have a lot to learn....

Thanks everyone!

 

[Tony k]

I see what you mean RC. IMR intended their powders to have relatively consistent performance across a broad range of conditions. Compared to ball powders, they succeeded. Hence they are "Improved."

Yep, I'm just trying to be cautious and avoid "surprises." I really don't think I'm pushing my rifle or my luck. I just don't always believe what I think

For the record, your sage advise is always helpful, and I always appreciate when you chime in. I just needed clarification in this case.

 

[gamestalker]

I'm pretty well known around here for my full tilt work ups, IMR-4350 has been a long time powder of choice I used for .270 win, still use it, and I use 130 gr. projectiles nearly exclusively. So maybe I can shed some light on this, though RC pretty much covered it all in a nut shell.

Depending on the brass, which makes a major difference regarding pressures, I run a load of between 54.0 grs. and up. I won't specify the max charge I run, lets just say I do push the ragged edge, yet still within published data. IMO, the single most common pressure factor to be considered with high pressure bottle neck cartridges, is the brass.

Now to address the effects of temperature. I lived in N. Az. for about 7 yrs., so winter temps would often be well below freezing, any where from 5 or 10 degrees, to low 40's. Then after moving back to the S.W. portion of the state, summer temps would very commonly run triple digit, 100-115 degree's. This said, I think it's safe to say I have experienced both ends of the spectrum and can provide realistic assessment, with my rifles, brass, and seating depths. Since I also usually seat up to, or into the lands, the effects of temperature are often very noticeable.

So, with max loads that had been worked up in the cold weather, that when fired in temps at or above 100 degree's, I did experience some obvious, multiple pressure increases. Signs of excessive primer flow, bolt face / extractor button transfer marks, an obvious increase in velocity, and stiff bolt lift were all very discernible and present.

And in cold weather, the loads that were developed in very warm weather displayed some very obvious and multiple signs of significantly lower pressures. Collapsed shoulders, decreased velocity, gases blowing back over the shoulders were all present.

All my finding were assessed using multiple methods, including velocity (chrony), case head appearance, primer flow ( I only use CCI's), and bolt lift.

BTW, without looking in my log book, I may have the temperature effects reversed. It could be that I experienced higher pressures with high temp developments being fired at extreme low temps, and low temp developments producing lower pressures in high temps.[/B] But unless my recollection is flawed, and it could most certainly be, but I'm fairly certain I had it right the first time.

All this said, it's always best to develop loads in, and for the temperatures you intend to shoot them in. And as I mentioned, use matching head stamps, sorted by weight when possible to avoid large variations. If matching head stamps are unavoidable, then at least try to sort them by wight.

GS

 

[Captcurt]

I have loaded IMR-4350 for over 40 years. It is my goto powder for many calibers from 243 to 300 WSM. There have has been times when I developed loads in 30 degree weather and found pressure signs when I shot them in 90 degree, but I was loading at or near max in those instances. I think that a lot of it hinges on the particular gun that you are using. Chambers vary, bolt faces may not be true, leade may be too short forcing you to seat your bullets deep. Now I test loads when the weather is moderate with temps in the 70's and I don't try to make a 270 mag out of a 270 win. The 200 or so whitetails that I have taken never knew the difference.

BTW, the 54gr load of IMR=4350 and a 130gr Speer is "MY" load for my 270.

 

[Tony k]

Thanks GS and CapCurt. I see many people settling on 54 grains as their "go to" with 270/130gr. My suspicion is that I'll end up right about there, but I think I'll continue with load development as I normally would at this point. However, I think I'll redo the upper end of the work ups (say 53.5-55 grains) in warmer weather just to be sure I'm not overpressure with this gun. That happened when I was working up loads with Hybrid 100v. Found a good load in January when temps were about 10 degrees, then used it on a Bear in August when it was 80 degrees. The three rounds I fired all had obvious bolt face extractor button marks. That experience has made me leery.

GS, I was using 1x fired hornady brass. While the brand was the same, there were some variations in the headstamp and rim shape (brass acumulated over several years). I didn't sort the brass by weight or volume. I've set the OAL to 3.31, which,is about .06, or .07 longer than Lyman and Sierra have listed. I used a hornady OAL gauge to set the bullet to be about .020 off the lands.

BTW, without looking in my log book, I may have the temperature effects reversed. It could be that I experienced higher pressures with high temp developments being fired at extreme low temps, and low temp developments producing lower pressures in high temps.[/B] But unless my recollection is flawed, and it could most certainly be, but I'm fairly certain I had it right the first time.

When I first started researching this subject, I came across an old thread that mentioned that AA4350 had inverse temp sensitivity (higher pressure at lower temps). Maybe that's what you are thinking of?

Thanks again everyone.

Tony

 

[gamestalker]

Ya, like I said, I haven't referenced my logs to see which conditions increased pressures, but pretty certain it was when going from cold development, to warm shooting conditions.

But of all pressure effects, head stamp / case weight / brass thickness, has always been the biggest single factor over the years for me. Sorting, though timely and tedious, is worth the effort IMO, and especially so if working up into the upper end of the tables.

GS