When Rolf and I shot the ASI match last month I commented:
My powder puff loads failed to reliably cycle the action. The cool weather probably contributed to this. In the hot (for the Seattle area) summer the loads cycled the same gun just fine. I think I need to add another 0.1 of a grain to the load to make sure they work in the cooler weather.
I tested my new loads today. They worked great. I tested them in two different guns and also tested the old load. Both guns cycled the action without a problem with the new loads. The old loads had a few problems in the cool weather.
The 0.1 grain increase in charge also decreased the standard deviation:
|Gun||Bullet Weight||Powder charge||Mean velocity||PF||Sdev||ES||Min||Max|
The group size was significantly smaller as well. This may have been because of the decreased standard deviation. A 140 PF is still very pleasant in a .40 S&W gun.
The bullets were polymer coated lead bullets. The powder was Hodgdon Clays.
Have you ever tried throwing a few loaded magazines into the fridge or freezer for a couple of hours just to see if they’ll still cycle your action when they’re cold? Just a thought.
I have not.
It’s a good thought. It would be a bit tough to get them to the indoor range while still at a known temperature. But I could do it at my range in Idaho. I’d run them over the chronograph for the definitive answer. It could be the temperature is affecting the lubrication of the gun rather than the bullet velocity.
Cooler bag with some cold packs?
Or just heat them up to 80, before you shoot them? The 1/10 grain powder addition seems the most positive solution.
And not having to ponder weather conditions to go shoot.
Looking at it in terms of the moniker, “practical shooting”, operating on the ragged edge of mechanical failure, necessitating a tweak in powder charge to compensate for weather, doesn’t seem to be all that “practical”.
It brings up the next question, which is the ES of your charge weights when progressive loading large numbers of cartridges. Only a few of the very best metering powders will generally hold to an ES of 0.1 grain, with double that variance (+/- 0.1) being a general claim in the loading industry. I haven’t used Clays, but it must be an awesome metering powder.
The charge weights are less than +/-0.1 (the resolution of my scale) for sample sizes of 10. The sport is “practical” in the sense that you are learning to move and shoot accurately (much more so that USPSA) and quickly. They allow, and I have used, a .22 for the matches with no scoring penalties.
Recoil management is better learned in USPSA where there is a minimum Power Factor.
Even though they are related the ES of the velocity is more important than the ES of the charge weights. The ES of the 3.1 charge noted above is well within acceptable values. That was with a 20-round sample.