Home Forums Reloading Big Game Rifles Pls help me understand high temps and increased pressure

I know heat can cause an increase in pressure. My question is, by how much. Say I have a medium warm load that shoots well at 65 degrees. Then I go hunt somewhere and it’s 100 degrees. Is my same load now potentially unsafe? At what point does this become a concern?

Different powders respond differently to specific temperature changes. Some show a very pronounced pressure increase.....while others are relatively stable! memtb

It will vary depending on the powder. Some powders pressure spike more than others in hotter temps. I would imagine a "medium warm" load will be fine. It usually the guys running on the hot side of things that would need to worry. That being said, its reloading and anything can happen.

For this very reason, I pretty much only use the Hodgdon Extreme powders now. I may be able to squeeze another .2 off a group with say Reloader but the lack of temp stability is not worth it. Invest in a chrono and cheap laser temp gun. Leave your gun and ammo in the sun one day and shoot your loads while recording temps. Ive used H4350 and IMR 8208 XBR in single digits up to mid 90s and saw less than 10 fps swing. My factory 45-70 Hornady Leverevolution ammo saw 100fps swings.

In my experience.... temp sensitivity has more to do with load density, than it does with the actual powder in question. The exact same powder can show different velocity swings under identical temp deltas.... depending on the cartridge/load. I seem to remember JB mentioning this same thing years ago in an article on the subject of temp sensitivity.

Interesting. I don’t shoot any compressed loads. Most of my handloads us RL 22, TAC, and H4350.

I bet you'll see a lot of velocity variation with RL22 and very little with H4350 and varying temps

I’ve seen times of both.... with both....

Right, there are no absolutes in this game. Just the probabilities.

The challenge is, I live in Southern California where the temp doesn’t change much at all. But I travel to hunt all over. Got an Axis deer hunt in TX mid summer. Hence my question... should I load some rounds down to be safe? Or is there a generally accepted safe “rule of thumb” already? Say 1-2 gr below max, which is where I am now for the most part.

Some of the old Speer manuals had a chart . This showed the velocity changes at different temperatures. More modern powders have caused these changes to be minimal. Hasbeen

“Available case is wasted space”! If it don’t fit....force it! memtb

Same here, hence why I just chose to go with a temp stable powder. I don't know of any rules of thumb but 1 or 2 grains below max I would imagine would be fine, especially if youre talking about a book "max"

Similar info on the R26 thread. As MD and others have posted all powders will show some increase in hotter temperatures. Many of the newer powders will show little variation in the 0-70 degree range but they all will gain velocity and pressure at over 100 degrees. Most of my hunting is in the 10-80 degree range which is not significant with most powders even some of the worst offenders. That and I don't shoot game at extended ranges where it could make a difference.

It would seem that the thing to do is to develop loads for a given round at varying temperatures (not sure what increment would be best), then segregate them and carry an assortment when hunting. When game is spotted, check the AMBIENT temperature (not some temperature a thousand miles away or in a heated building nearby), get harnessed into your sling, set up your shooting sticks, set wind flags at appropriate intervals between you and the animal in question, spin dials as dictated by distance, then select a round appropriate to the temperature, load rifle, and shoot.

It depends completely on the powder and the load.

Just to understand how bad the situation can be in the worst case, it's entirely possible for a non-temp stable load worked up at 70 degrees F to gain +10KPSI and a couple hundred feet per second fired at 140 degrees which is very possible for a dark colored gun in the hot sun.

To give you an idea, most guns are designed to be proofed with loads that are 25% over pressure. So a .30-06 that normally fires at about 60 KPSI would be proofed at 75 KPSI. That's enough margin that a load that was not over pressure to start with will typically not exceed proof pressure fired hot. So a kaboom is unlikely. However it may very well impede the function of the gun, sticking the bolt shut or blowing a primer for example. A load that was just a "little" over pressure to start with may very well be past the strength of the gun when hot. Which is a good reason to load to velocity with QuickLoad rather than trusting frequently erroneous pressure data from other sources.

The more recent Hodgdon Extreme powders, the new IMR Enduron powders, and Alliant RL-16, RL-23, and AR-COMP are the most temp-stable powders that I've got available. I almost always use one of the Hodgdon or RL-16/23/AR-COMP series (the IMR ones are slow and useless as far as I can see). If you load on a velocity node with one of those powders at 70F with a high brisance pimer, you will see essentially no velocity change between 140F and -20F. The velocity node part is key.

Or you could just use a temp-insensitive powder and load on a velocity node.

I think he was making a point that people are overthinking it.

Preach on, in spite of the fact you didn't recognize RL26 as a very temp stable powder. Keep up the good work.

I don't have any personal experience with it but from what ive read, its still not on par with the Hodgdon Extreme line?

I've got limited experience with it myself. Pay particular attention to the posts by Jordan and Mule Deer.

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