Thread: .270 muzzle speed

Here's what Sierra says for their 30 caliber 168 grain HPMK G1 BC:

.462 @ 2600 fps and above
.447 between 2600 and 2100 fps
.424 between 2100 and 1600 fps
.405 @ 1600 fps and below

Originally Posted by Woody

Here's what Sierra says for their 30 caliber 168 grain HPMK G1 BC:

.462 @ 2600 fps and above
.447 between 2600 and 2100 fps
.424 between 2100 and 1600 fps
.405 @ 1600 fps and below

So the issue is that the magnitude of these effects is so much smaller than the realistic uncertainty and precision of all the measurements in your system.

Using a .4 G1 270 bullet at 2800 fps, a 5 metre ranging error (395m vs 400m) the difference in POI is 3.5cm (about .1mil).

Comparing that bullet at 400m to the same parameters but BC of .42 G1 (a higher difference in BC than the example provided from >2600 cf 2100-2600 which is only a .15 change) gives only 1.9cm of difference. You cannot meaningfully measure this in the systems we're talking about with the precision of the measurements available.

"Truing trajectory" is a way of fudging some of the numbers to make your model with all it's various imprecise measurements fit observed reality, but it is not accurately measuring BC.