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Old March 29, 2010, 03:33 PM   #1
.284
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Holy hot loads.

Just wondering if anyone had an opinion as to why the loads I shot today are so much faster than the published data.

I am shooting a S&W 629 8 3/8" barrel in 44 Mag. I got the load data from the Sierra manual. I loaded 23.7 grs of 2400 (not max load). I used RP brass trimmed to the proper length, CCI 350 Mag LP primer, and a Sierra 210 gr JHC. The published data says 1400 ft/sec shot from a Ruger with a 7 1/2" barrel. I corno'd mine at an average velocity of 1609 ft/sec. That seems like a considerable difference to me??
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Old March 29, 2010, 03:38 PM   #2
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Quote:
why the loads I shot today are so much faster than the published data.
Cause Sierra didnt use your gun to test their loads.
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Old March 29, 2010, 03:38 PM   #3
Brian Pfleuger
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How far were you from the Chrony?


Alliant shows a velocity of 1566fps with 23.5gr of 2400 under a 210 Speer GD bullet with a 7.5" barrel so I don't think that you're necessarily too far off considered the difference in barrel length.
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Old March 29, 2010, 03:58 PM   #4
.284
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Peet, I was about 10 ft from the crony. Maybe Sierra doesn't have the correct velocity. Your data makes a bit more sense. I have found that any firearm my partner and I test is off from Sierra's data but it's usually not that much and we chalk it up to different test weapons. I just thought 200 ft/sec difference might be something to be concerned about. Maybe not?
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Old March 29, 2010, 09:17 PM   #5
Brian Pfleuger
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Well, I ran the data in Quickload using generic cartridge/bullet lengths and although the pressure in QL doesn't match well (at all) with revolvers, it does show a velocity difference of about 60fps between a 7.5" and 8.75" barrel. I would suspect that the real difference in a revolver would be less, due to the gap, but considering that you've got an additional .2gr of powder, I'd say that the book numbers and your numbers are actually in excellent agreement.

Subtracting the 60fps from your numbers put you just 3fps off their numbers.
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Old March 29, 2010, 10:13 PM   #6
Jim243
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I thought min distance to the Crony was suppost to be 12 feet?

Jim
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Old March 30, 2010, 01:54 AM   #7
FrankenMauser
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I thought min distance to the Crony was suppost to be 12 feet?
It depends on the brand, model, and (for some) lighting.
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Old March 30, 2010, 09:14 AM   #8
Brian Pfleuger
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Quote:
Originally Posted by Jim243
I thought min distance to the Crony was suppost to be 12 feet?

Jim
Quote:
Originally Posted by FrankenMauser
It depends on the brand, model, and (for some) lighting.
It also depends on some factors with the gun and particular load combination. For instance, if there is a lot of unburned powder when the bullet reaches the end of the barrel, or just uber-powerful magnums cartridges, then there could be substantial muzzle blast, which could cause erratic and just plain wrong readings if the chrony is too close. Also, there is the issue of muzzle blast acceleration, which is caused by the bullet "uncorking" the barrel and the now rapidly expanding gases actually accelerating the bullet beyond "true" muzzle velocity. I've been told that it takes about 25 for the bullet to lose the additional velocity and return to true muzzle velocity. Certainly, this effect only matters under certain load development conditions but it is there, nonetheless.
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Old March 30, 2010, 09:38 AM   #9
RickV
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Does the load call for the Magnum Primer? That may be the culprit.
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