Originally Posted by Bub10x
Really was a bit of a let down... Now I know it was cold and that showed from the early groups about a 20 fps drop but the box quotes 1275 a 225 diff.
One thing to consider regarding the DT loads is the altitude and temperature at which they were tested. We know Cedar City is at 5900 feet and while we don't know the temperature, elsewhere on Glock talk there are references to Doubletap loads being tested at 86 degrees F.
At a standard pressure and dew point this would yield a "density altitude" of about 8900 ft. Since you are at only 300 ft and 30-40 degrees F, I would wager that you would see a significant increase in recorded velocity in your loads if you were testing them at 8900 feet!! Incidentally, the density altitude for your location and temperature is roughly negative 1300 feet.
I have no idea what Doubletap does or doesn't do regarding testing so we can only speculate based on varying environmental conditions, but pressure and temperature are important parts of the equation to consider, and the difference between (-1300 feet) and 8900 feet is quite significant. I believe the difference in velocity is roughly 18%, and 82% of 1275 is equal to 1045.5 fps. You recorded 1050 fps.
I reserve the right to be incorrect as it's well past my geezer bedtime.