i was at the range today clocking some load and accuracy testing a few loads. i had my loads in a plastic ammo box on top of the bench. my loads seemed to get more consistant with velocityas the session went on, the temperature was about 90 and the sun was out full. when velocity testing the loads showed no obvious sign of pressure, but when i group tested, the primers got a little flat, not fill the pocket flush and push the primer back around the pin flat, but take the radius off the primer flat. This group was phenomenal, 3 @ .14 on center and 5 at .52 on center at 100 yards. what should i make of this, i know this probably isn't enough info but i know you guys know the questions to ask to help me out

Don't let your ammo get hot, it raises pressures, that is the lesson for the day!!!

Lesson Learned! what is the possibiliy that the increased pressure resulted in the tight group? is it likely that i can get the same performance with lower temp ammo? i know i will probably have to test to find out but should i be expecting the same size group or would my expectations be unrealistic

Probably not the pressure, exactly, but rather the increased velocity changes the barrel harmonics a bit.

Now, if you increase the powder charge, you might get better accuracy. But if you leave the cartridges with more powder in the sun, you might get even higher pressure.

So..... does that make sense?

Yeah, that makes sense. I will be retesting the load and keeping my ammo shaded from now on.

Yeah, that makes sense. I will be retesting the load and keeping my ammo shaded from now on.

In some guns for some loads, even holding the rounds in your hand on a cold winter day (well, it doesn't get THAT cold where I live, so let's say a COOL winter day) will move the POI over a round sitting in the ammo box at air temp. It's neat to see the difference. Doesn't work as well in all of my guns - at least not with factory loads.

KJ

I was using hodgdon benchmark which is supposed to fairly insensitive to temperature, but when the loads are getting real warm to the touch, i can understand the fluctuation