Finally got in a range trip today. It was 61*F. Still cool, but better than the 40s. Today I compared 57.5gr vs. 59.0gr of H1000 with 153.5 bergers in virgin ADG brass with CCI BR2 primers. The brass was chamfered, neck lubed, and expanded with a .262" mandrel before loading. Rounds were seated to a CBTO of 2.246" +/-.001". This results in a COAL of 2.950"-2.960". I ran everything out of an AICS short action mag today and had zero feed issues.
First off, I measured the capacity of my brass. Once fired, unsized brass has a capacity of 68.7gr of H20.
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These rounds were loaded about a month ago. Since they are compressed, I was worried the compressed powdered may push the bullet out with time. I checked the CBTO before I left for the range and everything was 2.246" +/-.001" as it should be.
I ran the same test with each charge weight before moving onto the next test. I have a temperature sticker on my barrel and I left it cool down to this point before each test.
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The order of my tests:
- 1st test: 5 shot group. I shot slowly and inspected each piece of brass as I shot it.
- 2nd test: 5 shot string. I broke a shot every 10 seconds to simulate a match-like environment.
- 3rd test: 8 shot string. Same as before. 1 shot every 10 seconds.
First off. Holy shit. What even is the point of seating depth tests. These were my two 100 yard, 5 shot groups from the 1st test. 57.5 gr on the left. 59.0 gr on the right.
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57.5gr averaged 2927 FPS over the day and 59.0 gr averaged 3002 FPS. This is out of a 28" barrel that after today, has 80 rounds on it. Both of these averages are at least 50 FPS faster than when I ran my velocity ladder a few months ago in 40* weather.
I saw no pressure signs on the brass. For the most part, the bolt lift always felt fine. This is very subjective, but the bolt lift may have got slightly stiff towards the end of that 8 round string with 59.0gr of powder. This is anecdotal evidence at best, but I will still probably play it safe and stick with 57.5gr of H1000. The barrel will probably speed up a bit more, and on a warm day, 2950 FPS will be sufficient. If that sticky bolt lift does become a problem, I don't want to risk it with the 59.0 gr charge. 50 extra FPS isn't worth having problems during a match.
Here's the velocity data. The SD and ES of each charge weight was a bit sporadic. I am hoping this improves with time. The barrel is young and I've had past barrels behave similarly. Also, with other cartridges, it seems like my velocity data got more consistent after the brass had 1x firing on it, but I have never collected data on this. 57.5gr had an SD of 14 and ES of 47 for the day and 59.0gr had an SD of 10 and ES of 38 for the day These are close enough in my opinion to be treated as the same.
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And here is the fired brass. This all looks fine to me:
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