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Old November 9, 2010, 10:41 AM   #1
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Trail Boss in .357

I loaded 5gr. of Trail Boss under 122gr. 9mm lead trunicated cone bullets and also 158gr LSWC. I test fired 10 of each over the chrony and got an ave. velocity of 855 for the 122s and 720 for the 158s. The 122s were very accurate, the 158s not so good. I then went up to 5.9grs of Trail Boss under the same 2 bullets. Test firing 10 rds of each came up with 609ave. velocity for the 9mms and 774 for the 158s. Does this make sense to anyone? Same primers, same brass, same day. I can't figure out why the 122s were over 200 fps slower with 1grain more powder,
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Old November 9, 2010, 10:55 AM   #2
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Two possibilities. One is that you were too close to the chronograph. I always use 15 feet now. Too many folks trying to make 6 feet work get false highs or lows from muzzle blast.

Second possibility is that with the case more full, the primer developed enough pressure to unseat the bullet before the powder burn caught up, so it was like shooting in a bigger case and got lower peak pressure. Usually the velocities are inconsistent when that's happening.
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Old November 9, 2010, 11:04 AM   #3
Brian Pfleuger
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Do you know that those loads are WAY over max published by Hodgdon/IMR?

They show 4.2gr as max load under the 158gr LSWC.

I don't know the case capacity and all that right off but I suspect that your problem may that you are compressing those loads.
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Old November 9, 2010, 11:07 AM   #4
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way over charged....
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Old November 9, 2010, 11:23 AM   #5
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I'll check my records, I was going by memory and I had also loaded some .44mag with Trail Boss so I may have quoted the wrong powder weight on the .357s. I know that even the 158gr. bullets did not compress the powder.
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