POI question

[K3]

I loaded .300WM rounds 2 ways.

1) 180gr Sierra SBT, Win LR Primer, Remington Brass (new), 58.5gr IMR 4895

Group result was 1-1/2 high at 100 yards. Muzzle velocity averaged ~2805fps.

2) 180gr Sierra SBT, Win LR Primer, Remington Brass (new), 71.0gr IMR4831

Group result was dead on zero at 100 yards. Muzzle velocity averaged ~2870fps.

I made no adjustments to the scope.

Can somebody explain this? I would think that with such similar muzzle velocities that the POI at 100 yards would be roughly the same. What gives?

 

[R.W.Dale]

Powder burnrate barrel harmonics and many many other variables other than velocity can effect POI quite dramatically. Your observations don't surprise ma at all.

 

[USSR]

Using a faster burning powder at a slower velocity will always result in a higher POI at close range. It has to do with the earlier pressure spike and the longer time that the bullet is in the barrel.

Don

 

[K3]

krochus:

As I'm new to reloading, it doesn't surprise me there's more to it than a simple equation. At least I make accurate ammo capable of better groups than factory loads, though I am ridiculously slow when reloading.

Do you know of any sources that would be good reading so I could learn a little more about this sort of thing?

 

[K3]

Using a faster burning powder at a slower velocity will always result in a higher POI at close range. It has to do with the earlier pressure spike and the longer time that the bullet is in the barrel.

Don

Would I be correct in applying the usual ballistics tables after the bullet leaves the muzzle in both cases? I would think so, but I've been knwn to be wrong a time or three.

 

[R.W.Dale]

http://www.the-long-family.com/OBT_paper.htm