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Old April 16, 2010, 08:40 PM   #1
.284
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Over pressure signs

I hear about over pressure signs all the time and I think I know most of the signs. However, I want to make sure.

What are all of know signs of over pressure loads? Are there differences between the signs on rifle brass and pistol brass? How about caliber?

I've been reloading for about 2 years now and not sure if I've had over pressure issues or not. If it helps, between my partner and I, we reload for 25-06, 280, 30-06, 22-250, 357, and 44 Mag.
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Old April 16, 2010, 09:28 PM   #2
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I think you will see the same over pressure signs in the .357 and .44 magnums as you would in rifle cartridges. Since the cases are fully supported you would see the tell-tale signs of cratered or flattened primers, flattened headstamps and hard to extract.
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Old April 16, 2010, 09:41 PM   #3
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UncleNick has a very thorough list... which I can't find a link to at the moment... he, or someone, will likely be along shortly to provide direction.
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Old April 16, 2010, 09:59 PM   #4
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The link is here:

http://www.shootersforum.com/showthread.htm?t=58763

Revolvers often do not share the same pressure signs as rifles, though they can. In particular, for reasons I'm not clear about, revolvers can sometimes actually burst without flattening the primer. Depends on the gun. In a revolver any kind of sticky or hard extraction means the cylinder steel is being stretched beyond the elastic limit of the brass, then grabs hold of the brass because the more elastic steel can spring back smaller than the brass can. That's a sign that you need to back the load off 5%. The pressure at which it happens varies from gun to gun, though, so there's no way to determine a safe load for all guns with the same chambering like that.
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Old April 17, 2010, 07:57 AM   #5
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Well, I almost just PM'd Unclenick instead of posting this thread. I didn't figure this would be 5 pages of answers and debated for weeks like some other threads. However, I hope it gets many many views. This is something every new reloader should know and experienced reloaders should be reminded of from time to time.

Personally, I knew the major stuff and was concerned because I do have primer flattening (if not darn near cratering) with my 44 mag. I do run mostly my hunting loads through the gun (Sierra 210gr JHC, W296@ 26 grs, CCI large magnum pistol primer, and RP brass). The gun is S&W 629 classic 8 3/8". I 've never had an issue with extraction and have not seen gas leaks around the primer. The chrono does not indicate higher velocity than what it is suppose to be.
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Last edited by .284; April 18, 2010 at 09:06 PM.
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Old April 18, 2010, 10:38 AM   #6
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handgun overpressure signs

The first sign is when loads exceed any published maximum, ay?

IME there is often NO sign that the pressure is unsafe, until your chrongraph tells you (although there WAS this one 44 Magnum case that required a big hammer to remove from the cylinder, once we'd hammered the cylinder open. The case looked a wee bit funny, and the headstamp was gone. Ruger service was great.)
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Old April 18, 2010, 03:17 PM   #7
Brandy
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CHRONOGRAPH is....

the answer. If you loads exceed published maximum velocity for THAT bullet, case, primer & powder, you are at risk.

You can do that and NOT have a hard bolt lift, cratered primers, hard extraction or any other "conventional" high pressure signs. Trust the chronograph!
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Old April 18, 2010, 03:59 PM   #8
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Watching for a published maximum velocity only works in theory if your barrel length is the same as the one the test data was taken with. So be sure you know the barrel length difference compensation for the bullet and powder you are using. But aside from that, for a given powder, if your gun's chamber and cartridge case dimensions are bigger than the test firearm's were, you will get to the same velocity at lower pressure than the test gun did. If they are smaller, you will get there at higher pressure.

That's why chronograph instructions almost always include a warning that you should not rely on them for determining powder charges by matching published load velocities. You see a lot of tales of false triggering and lighting and other issues that can affect the instrument's accuracy. So use the chronograph as another source of information input, but simply subbing it for keeping an eye out for pressure signs isn't safe. Pressure signs show up at different pressures in different guns or with different components. There's no reading an absolute pressure from them, nor guaranteeing you'll get to a published velocity before they show up.

Where the chronograph is maybe more useful is in checking your replication of another load you chronographed on the same machine under the same conditions, or in checking consistency of your loads. You might use it in a side by side with samples of your last loaded round to help you work up a new one using a new lot of primers, brass, bullets, or powder. But still keep an eye out for pressure signs.
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