Reading Group Shape

Just thought I would check back in. Was at the range today, er, I mean I left work sick at lunch........ Off the bench at 100 yards, the handloads found a sweet spot. From a previous session with the CHRONY, the 142 SMK are averaging 2832 fps with 50.5 gr of H4831. Today, I was going to shoot 11, 4-shot groups. I worked up starting at 48.6 and stopped at 51.3 with the groups opening back up, some firing pin splash, and early signs of flattened primer. 51.0, however, was the best I have ever shot, and that 4-shot group makes a nice little triangle that is 0.545" across, outside edge to outside edge, and 0.384" center to center, as best I can measure. My thinking about group size is that the outside to outside distance minus one bullet diameter should equal or be the same as the center to center measurement. It is not in my case. What gives ??

I'll try the 300 and 600 yard ranges next week with loads in this vicinity.

How, exactly do you all measure group size ??

Thanks.
 
One Possibility

Flouncer:

Both your groups have that 10 o'clock to 4 o'clock pattern.

That "could" mean WIND.

With the right hand spin of the bullet, a wind from 9 o'clock will drift the bullet down a little (about 25% as much as the drift to the right).

A wind from 3 o'clock will drift the bullet up a little.

Same idea as the spin put on a baseball by a pitcher. Same thing that causes an airplane wing to lift the plane. Some folks call it the Bernoullii effect. Others say it's got to do with the bullet pointing into the wind.

Anyway with only two groups, it just one of may possibilities. If you see that 10 o'
clock/4 o'clock pattern on several groups, it might be telling you ya better learn more about wind drift.

Ya got some wind flags out there when ya practice?

Joe Haller :)
 
Thanks Joe. Here are pics of the above firing...... Yeah, there's flags all over the place, and in this case, I could feel it .. .. .. COLD !! Maybe 5-10 mph left to right, almost 90 deg and perpendicular to the axis off flight. But it's only 100 yards and I tried to time the wind .....

IMG_0128.jpg


IMG_0129.jpg


.. .. .. and here is where I called it a day, and the primers looked abused. Not able to get a decent closeup of the primers with $100 Fry's camera.

IMG_0131.jpg
 
You must log in or register to reply here.
Back
Top