temp sensitivity

[cnote]

If a known powder is temp sensitive and shoots to a 170 PF at 65 degrees F, does an increase in temp up to the 90's (you don't shoot all the reloads again until the middle of summer) make the rounds potentially dangerous.

I'm just wondering if it is safe to reload my rear-end off during the winter months to prepare for next season.

I guess I could just go with a set formula that I already have, but then I may not be able to experiment with new powders/loads.

AM I just paranoid?

Thanks

[shred]

Every powder is different in that regard. Most of them get hotter as it gets warmer, but by how much when varies. I don't know anybody currently publishing that data. Vitavuori had some text along those lines in one of their early early pamphlets, but it's since been deleted from later versions.

Best bet is to chrono some that have been kept in a warm spot to be sure.

[G-ManBart]

If you tell us exactly what powder someone might be able to tell you whether it's positive temp sensitive, neutral or negative temp sensitive. For example, IMR 4756 is reverse temp sensitive....the colder it gets, the higher the velocity.

[cnote]

I live in the Midwest with crazy temp fluctuations and also all 4 seasons.

I am thinking of going with tightgroup ( for plated bullets), which i read/hear is very positively sensitive. I am also looking into moly coated bullets, which recommend WST which is inverse and people have gone minor with it due to the weather. The VV320 is hard to find and expensive.

So, would the tightgroup be potentially dangerous and the WST be putting me in a bad spot for scoring purposes?

Info for Universal Clays and HP38 would be some other options,

Thanks

Edited October 6, 2008 by cnote

[MichiganShootist]

Your summary is dead on regarding TG and WST.. I use only TG and a good shooting buddy uses WST. The TG gets slow when it's cold the WST gets fast when its cold.

Edited October 6, 2008 by MichiganShootist

[kevin c]

As mentioned above, many if not most powders are temperature sensitive, including the ones used in commercial ammunition. You'll see a little of that with change in environmental temperature, but also just from the round heating up in the chamber as the barrel heats up from being fired. For instance, with the very reproducible VV loads I use, I see the first round out of a cold barrel is significantly slower than the ones that follow.

Anyway, all that to speculate that the amount of heating from 60 to 90 degrees change in environmental temp is probably a lot less than that from a cold round cooking in a hot barrel, and that I've not heard of pistol ammunition going from reasonable to unreasonable pressures from either (rifle maybe?).

Like Shred says, chrono a few rounds to be sure, and don't start with some crazy-axx super high pressure load to start with.

[chirpy]

I have used WST in .45 for years and WW452AA (replaced by WST) and loaded to 180+pf and never had a bit of trouble keeping above major pf which was 175 early on. I have since dropped to 170+ and the same applies. After Winchester found out 452 AA was temp. sensitive the brought out their replacement powders which were supposed to be non-temp sensitive but that didn't prove to be the case.

Richard

[double_pedro]

There's a quick and dirty way to find out....put a few rounds in a zip lock bag in a cooler with ice & water (which will be at 32 oF as lonng as there is ice in the water). Leave 'em in there for a couple of hours and then chrono them. Compare that with chrono data from rounds at (known) ambient temperature. This will give you an idea of how much change per degree F you can expect and what the direction of the change is.

[cnote]

Thanks to all for the help. Keep it coming if you think it could help. Does anyone have any HP38 or Univ. Clays opinions v's the WST.

[shooterbenedetto]

IMR powder are very temp sensitive.

[cnote]

Anyone on HP38/ win231 forward or reverse sensitivity??

Edited March 5, 2010 by cnote

[Action Pistolero]

In my experience 231 gets faster as it gets hotter.

I've been using WST in my 9x23 minor loads for the past 6 years. I finally had a problem last year at Bianchi making the 120 pf. Turns out they were using a commander to test the loads and the rounds had been sitting out in direct sunlight. It was also a bit warmer than it had been in years past. Got called to the chrono and easily made it with my 6" barrel.

Put a box of rounds under the heater vent in the truck and make them warm to the touch. Shoot them over the chrono and see what you get. This would be a worse case scenario. In the hot months I leave my ammo in my shooting bag or loaded in mags but they are always in the shade.

[MichiganShootist]

I wouldn't recommend heating your ammo in the microwave.... but that's just me

[G-ManBart]

I've not heard of pistol ammunition going from reasonable to unreasonable pressures from either (rifle maybe?).

I think you could do it with 7625 (reverse temp sensitive) pretty easily. Come up with a nice 172-3PF load at 70-80*F and then shoot a match when it's in the 20s or 30s (we did that in NM). That would bump up the pressure a lot, and enough to start melting primers...probably because 7625 is on the fast side (for Super/SC) to start with. R,

[goat68]

Nitrocelulose based powders are reverse sensitive. IE faster burning at lower ambiant air temperature. Nitroglycerine based powders forward sensitive. IE faster burning at higher air temperature. Some companies have this information listed on their MSDS sheets.

[cnote]

Nitrocelulose based powders are reverse sensitive. IE faster burning at lower ambiant air temperature. Nitroglycerine based powders forward sensitive. IE faster burning at higher air temperature. Some companies have this information listed on their MSDS sheets.

so this if from Clays, thus it should tend to be reverse sensitive, opposite of searchs on here

cellulose >85%

glycerine 10%

additives non hazardous <10%

[cnote]

There's a quick and dirty way to find out....put a few rounds in a zip lock bag in a cooler with ice & water (which will be at 32 oF as lonng as there is ice in the water). Leave 'em in there for a couple of hours and then chrono them. Compare that with chrono data from rounds at (known) ambient temperature. This will give you an idea of how much change per degree F you can expect and what the direction of the change is.

This may be the only true answer, back to the basics "Rocky IV" style, because

Based on a call to St Marks in florida about their general MSDS sheets for the powders they make (for a lot of names/brands) on Hodgons site, they group them into one sheet. Individual powders recipes are proprietary secrets but he said all of them are Nitrocellulose based with differing ammounts of nitroglycerine included

Other sheets are not as general, like Clays

excuse the spelling

[SA Friday]

I personally view all powders as temp sensitive. I usually see the terms temp sensitive as the rounds get hotter as the outside temp gets hotter, and reverse temp sensitive as the rounds get hotter as the outside temp gets colder. Even though I view all powders as temp sensitive or reverse temp sensitive, I also believe the various powders have different degrees of temp sensitivity. Some I have tests have fluxuated much more than others. In some of my testing, WST fluxuated in the range of 5-6 pf. Universal clays was virtually unmeasurable in 40 cal when I was using it. Results vary for everyone and every gun based on all the variables of the load, the weather conditions, and powder lots. Chrono'ing your ammo under the varying weather conditions over a year of shooting and charting out the results in a data table is the best way to see just how sensitive the powder is to temp. Doing an initial test of reloads where one set is kept at a freezing temp and another set is kept at 80-90 degrees F is a good way to get a base line of sensitivity. IMO, as long as your pf isn't fluxuating below pf requirements or above pressure allowances, and is maintaining accuracy and POI, the powder is fine. I avoid powders I have to change the load for the seasons.