I did a little experiment with Retumbo the other day up here in Wisconisn. I have a fussy 300 wby ultralight and found a load that works great (fairly compressed) with retumbo and 180tsx's.
Anyhow shooting in 20-30 degree weather the load was doing 3200-3240. I was worried it might get a little hotter in say 70 degree weather.
I put some ammo in a 6 pack cooler with a zip lock bag of warm water in the cooler. I took a thermometer along and by the time I stopped for lunch and got set up the temp in the cooler was 60 degrees.
It was 10 degrees outside. I got my chrono and gun all set to go. I put the ammo in my pocket and the thermometer in there too. The thermometer said it was 60 degrees in my pocket. I sat by the gun and fired off groups of 3 shots. I'm not sure how fast the chamber of the gun could cool down a shell that was in there for about 15 seconds but by the 3rd shot of the string the chamber should have been at least room temp I would think.
Anyhow....the bottom line in my experiment was that all ammo was still doing right around 3200 fps. From what I saw it would appear to me that Retumbo was pretty temp tolerant from 20 degrees to about 60 degrees. Even if it lost a bit of zip in colder temps or gained just a tad when warmer I think I've proved to myself that in the temps that I would hunt in this powder will be consistant.
