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Too much pressure in the 300 RUM?

 
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  #15  
Old 03-31-2005, 12:15 PM
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Re: Too much pressure in the 300 RUM?

3sixbits: Are you sure you want to use .003" as a measure of case head expansion? That's a whole lot more than I'd want to see in any of my rifles. Maybe you missed a zero? I do agree with your statement: "If the head expansion is in excess of .003 you have exceeded the limits of safe pressure". I'd say that at .003" expansion it would vastly exceed the safe pressure limits.
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  #16  
Old 03-31-2005, 01:07 PM
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Re: Too much pressure in the 300 RUM?

[ QUOTE ]
3sixbits: Are you sure you want to use .003" as a measure of case head expansion? That's a whole lot more than I'd want to see in any of my rifles. Maybe you missed a zero? I do agree with your statement: "If the head expansion is in excess of .003 you have exceeded the limits of safe pressure". I'd say that at .003" expansion it would vastly exceed the safe pressure limits.

[/ QUOTE ] And a BIG THANK YOU ss7mm to you! You are correct and the post has been edited. Damn my computer for making such a mistake. NOTE one and all that reads @ .0003. This is and should be considered as having reaching above max safe working pressure. [img]/ubbthreads/images/graemlins/blush.gif[/img] [img]/ubbthreads/images/graemlins/blush.gif[/img] [img]/ubbthreads/images/graemlins/blush.gif[/img]
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  #17  
Old 03-31-2005, 01:13 PM
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Re: Too much pressure in the 300 RUM?

3sixbits: No problem. I just didn't want anyone to get hurt. Most listings you see for expansion list .0003" to .0005" at the most as maximum expansion to look for.
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  #18  
Old 03-31-2005, 01:23 PM
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Re: Too much pressure in the 300 RUM?

I think it's .0005" CHE, that's "ten thou" not thou.

Of course this is all relative and can vary a significant amount even if using the very best techniques. For decades this was considered a very good indicator of pressure but even the greats dissuade its use unless the inherant large margin of error is factored in.

.0003" CHE may tell you that your load is reaching/reached or beyond a max load, and that's the problem, you don't know where but you know it's in the area. I have measured loads that were near .001" CHE and then and only then were they approaching 65,000 psi on actual test equipment, then there were others that never even approached .0005" and were already running 65 kpsi. The baseline measurement was taken on once fired brass, not virgin, but once fired with medium load. The baseline case average diameter was then compared against the diameters from the same cases fired a second time. Beltless cases were measured immediately above of the extractor groove, or on the belt for a belted case. All case were measured relative to a specific mark on the casehead so measurement were always taken in the same place.

Pressure ring expansion is even a more accurate/consistant method but requires a blade mic and a method to control distance from the case base and where the measurement is taken in order to be accurate. A proper baseline etc.

Southwest Products PressureTrace is a very inexpensive method to attain the real pressure numbers, no guessing game. If you can test fire next to a computer (laptop most portable unless you shoot out the back door), this will work for you.

Here's a load I worked up using PT. Can you spot where the blast from my rifle shook the 5.0 gr slider weight on the beam scale I was using over one notch as it sat in the warm up shack three benches away where I was loading one round at a time? When I spotted the pressure increase and also the MV jump I went to investigate the scale. From that shot there, it had just jumped another 5.0 gr! Thank God I caught it when I did.


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  #19  
Old 03-31-2005, 01:41 PM
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Re: Too much pressure in the 300 RUM?

Thanks for the info guys. I see that the measurement goes to 4 decimal places. The caliper that I have only goes to 3 decimal places. So I don't think that I can get an accurate enough measurement of the case head expansion. Even if the numbers are the same, they could still be above the recommended .0005" Is there any other way that I check for exsessive pressure?
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  #20  
Old 04-01-2005, 02:33 AM
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Re: Too much pressure in the 300 RUM?

I once asked the same question to a tech st sierra, his response was that if all I had was slight primer cratering (in my stw) when using a fed 215 primer, it was no big deal. Federal primers are known to have a soft cup, if there are no other pressure signs then your loads not that hot, chances are you'll have cratering with loads that are below max pressure. Just check the casehead expansion as long as its below .0003 it will be fine.
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  #21  
Old 04-01-2005, 08:42 AM
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Re: Too much pressure in the 300 RUM?

As far as I can tell, there are no other pressure signs. I looked for extractor marks and didn't see any. The bolt opened fine, and that cases didn't seem to stick in the chamber. The only signs that I could see we in very slight cratering of the primers. The caliper that I have can only do 3 decimal places, so I don't think that I will be able to measure case head expansion very well.

Thanks for the tips!
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