Wind question

hadjii

Ok, so I've worked up a load for my 338 marlin express. 46.2 grains of LVR, pushing a 200 grain nosler accubond. 3 groups of 3 shots on 3 different days has yielded groups of 3/4", 1 1/4", and 1 3/8". Good enough for me. It has been dead nuts on @ 100 yards for these 3 groups. The wind was calm, or close to it for the 3, 3 shot groups. My range is oriented to where I shoot straight north. Today, there's an 11 mph wind out of the SSW. Also today, I shot another 3 shot group, and poi was 1 1/2" to the 6:00. My question is whether the SSW wind can be causing the change in poi.

On a side note, i bought a box of factory 338 max ammo. 1 3 shot group showed poi to be about 3-4 inches high from my hand loads, so I took one apart, and the powder charge was 51.1 grains. So I unloaded 3 more, reduced the powder charge to 46.2, which is what my hand loads are. POI was now 8" lower than my hand loads. Not sure what powder hornady is using, but I know this, it isn't LVR, which is what I assumed it was.

charliemeyer007

I think its what an 18 mph cross wind has the same effect on a bullet as gravity? Play with one of the ballistic programs to see.

Factory ammo as a rule isn't loaded with stuff they sell to us. Well that was the way it was, who knows what they do now.

62fuelie

Factory loads are done with bulk blended powder that is balanced by the manufacturer to produce consistent ballistics batch after batch. The available powders we buy over the counter are manufactured to produce the same, or nearly the same, burn rate and pressure yield lot after lot so we can be assured the loads we assemble, if we do our part, are also consistent. The two are not directly interchangeable in most cases. I don't know what loading data source you are using and whether you have chronographed your loads, but most load tables will offer one or more loads that come very close to duplicating factory velocities. Once this is found, if possible, then you should be able to find a hand load that will print with the factory load.
One thing I found when working on selecting a duty load for our P.D. was that Hornady's published velocities where somewhat slower than the chrono read them. This could mean that the bullet is in the barrel during more of the recoil rise as it is moving through it more slowly and result in a higher strike on the target.
FWIW
B

charliemeyer007

This program looks interesting to play with.

https://www.hornady.com/team-hornady/ballistic-calculators/4dof-ballistic-calculator/overview