POI vs powder load


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tt5
April 21, 2013, 09:26 PM
I've often read that POI will be lower with a faster bullet or heavier charge. I figured I'd post today's results as an example.
-Each green triangle is the average height above or below POA for a 5 shot group.
-The red squares are the averages for all 5 shot groups at a given powder load.
- The blue line is a linear regression of the whole pile of data.

https://sites.google.com/site/timgtaylor5/rfcstorage/poivspdr130421.JPG

This evening I processed the results of a pleasant afternoon testing WSF behind the Missouri Bullet Co's 9mm 125g LSWC. I use the "On Target" program to measure 5 shot groups, then punch them into excel to make sense of the numbers. The graph above was surprising in how clean the relationship is between POI and grains of powder (at least for this batch of data). Actually this is 2 days of testing. I ran the low end of the range a few weeks ago and figured out that I needed more powder. Today I ran 3.8-4.6g.

I had ejection problems at 3.6g and below.
Primers had a bit of a crater lip at 4.6g.
Group size and POI are both pretty good at 4.0-4.2g.

Now I'll see if any of the holes in my powder measure throw in that range, or if I have to make something.

Other details are OAL 1.075, cci500 primers, CZ75-SP01 pistol.

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