Chamber pressures

jmwyoming

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Feb 28, 2013
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Lost springs wy
Hey guys, where can I find out what the different chamber pressures are for my 300 Weatherby mag. I'm using IMR 7828 trying out loads from 80.5 grains up to the max of 84.5 grains as per nosler reloading book. With a 180 gr accubond. Thanks, John
 

Colorado Cowboy

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Jun 8, 2011
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It is almost impossible to find out chamber pressures on reloads. The various reloading manuals will list max loads which will be below max pressures. Why do you want to know? Are you having any problems....eg. blown primers, stiff bolt, etc?
 

jmwyoming

Active Member
Feb 28, 2013
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Lost springs wy
No, just wanted to keep them below 65000. A rep from nosler said that the max load of 84.5 would be below that. Just being cautious. I was hoping to hear from you C.C.
 

Tim McCoy

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Dec 15, 2014
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Oregon
I recall a gun writer getting some contraption to measure pressure, so I did a quick search. May have been Jamison, can't recall. Know nothing about it, and there may be other better systems. https://www.shootingsoftware.com/index.htm You can have higher than desired pressure without the traditional signs, happens, but the traditional signs are a warning to back off. I have had flattened primers and sticky bolts in two guns with factory loads, happens. Guns can be weird. When I reloaded, as long as I was under the book, without traditional signs, I called it good.

I read another expert say to use a chronograph, his contention was stop at the max book charge or max velocity in the book for that load. Not advocating that, as I'd be concerned about temp etc. Can't remember the guys name.

Might be fun to buy a pressure measuring toy and use it with a chronograph...
 

JimP

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Mar 28, 2016
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The big problem with chamber pressures is that what is a safe load in my rifle may not be a safe load in your rifle with the load being equal.

I have seen gun writers go as far as setting up a pressure gauge on their firearm to measure the pressures but that is going way too far for me. I stick to the usual means of measuring cases, primers, brass flowing, and sticking bolts to determine when I need to back off.
 

Colorado Cowboy

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Jun 8, 2011
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The big problem with chamber pressures is that what is a safe load in my rifle may not be a safe load in your rifle with the load being equal.
You are entirely correct. There are min/max dimensions on everything. While modern machining methods are very accurate, you can't make everything to net designed dimension. I'll give you an example. My Dad had a 03 Springfield and so do I (I have his now as he is gone). His gun has a chamber that is very loose (near max dimensions) while mine is just the opposite, very tight. His fired brass is so large that I can't close the bolt on it in my gun.

This size/tolerance band is why factory loads are pretty conservative. They just don't know what type of gun they will be fired in. This is whey reloaders can tailor their loads to their rifles and get great performance.
 

dan maule

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Jan 3, 2015
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Upper Michigan
Hey guys, where can I find out what the different chamber pressures are for my 300 Weatherby mag. I'm using IMR 7828 trying out loads from 80.5 grains up to the max of 84.5 grains as per nosler reloading book. With a 180 gr accubond. Thanks, John
Is your 300 Wby a Weatherby Mark V. The Mark V typically has a ton of free bore which I am told helps to reduce pressure spikes.
 
Yup, every rifle is a case unto itself. All you can really do is start at a known safe level and work up until the visible signs of pressure on the fired case are seen. This is the obvious without putting a mic on the case head. Chronos can be a very useful tool in disclosing a warning of pressure. If you notice a quick, substantial increase in velocity chances are you're entering the danger zone.