Posted 17 June 2007 - 07:24 PM
Well, the 760 load development experiment, Phase I, is complete. I assembled six more load tests for firing and proceded to the range with chronograph, rifle, notepaper and targets. The test loads were assembled with three rds for each load level. The powder charges were weighed in 0.5 grain increments. Tip of the Day: You can judge when your powder charges are starting to be excessive by measuring the case just in front of the extractor cut. The procedure is to measure the case before and after firing. Excessive expansion in this measurement is an indication of extreme pressure. Supposedly this only works with brass that has already been fired at least once. An increase in the base measurement of 0.001" is considered excessive. Note: Excessively annealled brass will also result in excessive base expansion and is still a danger sign, just the cause is different.Tip of the Day #2: If you have heavier than normal bolt lift after firing, you are probably experiencing excessive pressure. Tip of the Day #3: When your primers seat with very little or no force after two or three firings, it probably means you are in a high pressure situation. Dump those cases with loose pockets and start over. Don't do like one fellow I heard about and just use a little scotch tape to hold them in. Back to the load test. All the cases were once fired Hornady brass. The bullets were Berger 50 gr Match/Varmint. The case expansion measurements were taken at home after the test firing.Load #1: AVG - 3460, SD - 32, Grp - .57, Expansion - .371Load #2: AVG - 3503, SD - 15, Grp - .95, Expansion - .371Load #3: AVG - 3567, SD - 33, Grp - .58, Expansion - .372Load #4: AVG - 3628, SD - 33, Grp - .67, Expansion - .375Load #5: AVG - 3689, SD - 27, Grp - 1.26, Expansion - .375Note: Heavier bolt liftLoad #6: AVG - 3748, SD - 29, Grp - 1.04, Expansion - .379Note: Heavy bolt lift. Blown primer on last round. Too much! Last case stuck in bolt, had to beat it out.Lessons learned:1. Take calipers to range for load tests.2. After you get high pressure signs, stop.3. You can get too much 760 behind a 50 gr bullet in a 204 Ruger.4. Powder particles in the face sting, wear safety glasses!5. Load #2 has possibilities. Two of the three made a small figure eight.6. Not likely to get 3700 fps with the 50 Berger as a safe load with 760.Just thought I'd share this experience as what not to do, since some people have been talking about starting to reload.
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