For all the reloaders in the house... I found this today online. A lot of people are starting to use polymer coated bullets in their range ammo because they are, well cheaper, by a lot. There are also commercial loads available out there.

Then people started accusing Shooter's World Powder of being 'temperature sensitive' which is something that isn't exactly a compliment.

Here is the response from the company, which I found very interesting.

Hi Folks!

We have been recently inundated with questions about Clean Shot being temperature sensitive.

The predominant complaint involved Clean Shot and polymer coated pistol bullets. The claims were that as the temperature rose, velocity dropped. And conversely, as temperature dropped, velocity rose.

To a Ballistician, that's counterintuitive. Normally, as temperature rises, propellant pressures rise with it. It's part of Boyle's Law (PV=nRT).

So, with all due haste, we tested Clean Shot at 75 degrees F, and 125 degrees F. We shot Berry's plated 124gr RN, Hornady 124gr FMJ, and a polymer coated 124gr RN. All 9mm. We tested all these in laboratory conditions, from a test barrel.

Now, please bear in mind my history. I'm a competitive rimfire shooter from days-gone-by. I'm also an engineer, a tinkerer, a bullet caster since I was 17, and unverified internet rumors claiming "farmer" status. I digress...

I know a lot about bullet lubricant.

So, I theorized before the experiment: What happens to plastics when they get cold? (they get hard and brittle). What happens to plastics when they get hot? (they get soft and pliable). I wondered if this polymer attribute might have some effect upon ballistics...

The Findings:

When testing plated or jacketed bullets, between ambient and 125 degrees F, there is virtually no change in either pressure or velocity output. However, when using polymer coated bullets, I witnessed a SUBSTANTIAL loss in pressure at elevated temperatures. Likewise, I witnessed a loss in velocity at elevated temperatures. Keep in mind that my test barrel has a SAAMI min-spec bore/groove, lead and throat. Not so, with competition and production guns. With longer leads, more pressure can bleed off before gas sealing. I SUSPECT this might cause even more velocity loss when shot from a standard firearm.

How could this be possible? Well, it could well be that polymer bullets, because they're essentially coated in plastic, change their lubricity with changing temperatures. Jacketed and plated bullets seem to not exhibit this trait.

Could it be that there are some polymers out there that don't change their frictional coefficient with changing temperatures? Dunno. Do some polymers exhibit more temperature/frictional coefficient change than others? Dunno.

But what I can say today, right this very minute, is that polymer coated bullets dropped from 1072 fps at ambient to 1041 fps at 125F.

And plated or jacketed bullets changed no more than 10 fps between ambient and elevated temperatures. In fact, the Hornady FMJ changed only 5 fps between temperatures...

The truth shall set you free.


The bullet type and specific type of coating actually induced the problem, not the powder. Very interesting.

The source:

https://www.facebook.com/groups/2797...2/?__tn__=CH-R