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Some 30 Cal BCs Tested

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Unread 08-15-2006, 08:55 PM
Join Date: Dec 2004
Location: El Reno, OK
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Re: Some 30 Cal BCs Tested

Great info. Thanks a ton for sharing this. Just shows you that most manufacturers are a bit optomistic.
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Unread 08-16-2006, 03:13 AM
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Join Date: Dec 2001
Location: Mukilteo, WA
Posts: 1,092
Re: Some 30 Cal BCs Tested

Mike, I just needed to know how the chronos read relative to each other. If one read 20 fps higher than the other and I didn't know it, that would skew the numbers one way or the other depending upon whether I put it in front or back. The relative comparison between bullets would still be valid, but much less absolutely accurate.

As it turned out, Oehlers are good. [img]/ubbthreads/images/graemlins/laugh.gif[/img] One averaged 4 fps slower reading the same bullet than the other (accounting for the 1 fps the bullet lost between the two). I only shot three to come up with that, but they were all single digit differences with a max of 7 fps and an average of 4. So I simply added 4 fps to the readings from that one when figuring the BC's to put them on a level playing field. Had the difference been bigger, neglecting to do this would have had a larger effect. But the only way to know for sure was to find the difference in the first place.
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Unread 08-16-2006, 04:46 AM
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Join Date: Feb 2005
Location: USA
Posts: 2,598
Re: Some 30 Cal BCs Tested

Nice Jon thanks for info.............. [img]/ubbthreads/images/graemlins/wink.gif[/img]
range it,check the wind, dial in correction, aim and only one shot
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Unread 08-18-2006, 05:23 PM
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Join Date: Dec 2005
Posts: 181
Re: Some 30 Cal BCs Tested

Excellent work Jon, thanks for the effort. That's why manufactures and bullet makers hesitate to put a number on the BC of a bullet. I wish people would understand the number they are giving is a starting point or the number on that perticular day in that location they tested and don't critisize if they can't come up with a match. BP,humidity,temp,and altitude will certainly give different BC on a bullet. What powder or powders did you use for your testing?
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Unread 08-19-2006, 05:34 PM
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Join Date: Dec 2001
Location: Mukilteo, WA
Posts: 1,092
Re: Some 30 Cal BCs Tested

Here were the loads:

173 101 Retumbo
180s (all of them) 99 Retumbo
200 96 Retumbo
210 94 Retumbo
240 101 US869

Some of the velocities were higher than they should be. I was starting out the test with a dirty rifle and didn't realize I had forgotten to bring my cleaning stuff until I had everything set I said screw it and did the test anyway.

This makes a difference for some bullets because my throat is really tight and when there's a bunch of carbon built up in it some of the more pudgy-nosed bullets (240 SMK, 200 AB, etc) chamber with significant feel and marks will be on the bullets when removed. I think this sort of has a similar effect to jamming the bullets in the lands, increasing pressure and velocity.

Anyway, that's why a couple of the velocities are higher than they should be. For example, I chronoed the 240 load the next day with a clean rifle and it was right at 2970 where it should be.
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