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excess pressure?

 
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  #8  
Old 02-08-2012, 01:09 PM
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Re: excess pressure?

I've reloading for a very long time and usually load pretty 'hot' but have never blown up anything nor had a head seperation. Some things I've learned about pressure are:

* primers are such poor indicators of pressure I hardly pay them any attention. Excessively flat primers are most often a sign the case shoulders have been set back too far. Pierced primers most often signify a bad firing pin or one that's too small for the bolt hole. Primers that blow out at the edge of the pocket usually have defective cups OR the hole's radius is too large.

* ANY visable sign of high pressure on the case head is too hot, it takes a lot of pressure to make even a faint impression at the ejector/extractor location.

* Any measureable expansion of the head diameter just forward of the extractor groove says the load is too hot.

* A case with no obvious sign of over pressure but the primer pockets get looser each firing IS over loaded.


There's no magic 'back off' number for the charge; back off until you're consistantly below where the signs appear.
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  #9  
Old 02-08-2012, 02:33 PM
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Re: excess pressure?

I start load development by finding MY 'max load' with given components.
This has nothing to do with any load manual or velocity goal.
It's based on max load being a reloading problem, or not.
A defining line.

Bring calipers to the range when working up to find max. Pick a spot nearest the webs that you can consistently measure at(I use the webline ~.2 forward of extraction groove).
As you go up in pressure this datum will step change to a larger diameter that represents chamber minus springback. It'll hold at this diameter for further increments, but at some higher charge will step change again another .0005"(1/2thou). This represents the point of brass yielding and where FL sizing will be required. Barely above this you get popping extraction as the brass is left at an interference fit because the chamber sprung back fully, while the brass did not(yielded).

Primers,,, bolt turn,,, head marks,, brass life,, could do anything, or nothing, through the range -with your action, your chamber, your dies, and what you're willing to accept. Many point blank BR shooters accept only 2-3 firings of brass life with extreme pressure loads. But you can't accept their pressures with hunting cartridges. Too much area for pressure applied. You will run into real problems way lower in pressure.
Your chamber is your best die, and you're sizing in it (upsizing). So this will show any real problems, or not.
That's what you wanna watch.
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  #10  
Old 02-09-2012, 10:33 PM
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Re: excess pressure?

could the oal be a factor in the pressure? Ryan
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  #11  
Old 02-10-2012, 09:00 AM
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Re: excess pressure?

A lot of things combine to produce different pressures with a given load.
OgvOAL matters in that pressure step changes upward as a bullet contacts the rifling lands.
Bullet seating depth matters in that deeper seating increases load density a small amount, but in an extreme can compress a load. Also an extreme is seating to put bullet bearing into the neck-shoulder junction, where tension(bullet grip) sharply increases.

These are not always 'problems'. Many develop great loads with bullets jammed into lands, or seated deeply due to magazine restrictions.
But they can cause your pressures/velocities to differ from book listed.
Many other things can as well.
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  #12  
Old 02-10-2012, 09:13 AM
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Re: excess pressure?

I have pretty much ended up doing the same thing as Mikecr with measuring the cases.

FWIW, I measure the case head expansion on factory loads and then I usually end up with slightly less expansion in my hunting loads.


I have a rifle that makes a ring around the primer with loads that are not overpressure. I found that it is very sensitive to case length and likes cases to be closer to trim length than the published length.
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  #13  
Old 02-12-2012, 11:57 PM
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Re: excess pressure?

I asked SAAMI about this some years ago when I started reloading for my first belted magnum. The rep said most cartridge brass starts extruding into bolt face cutouts (ejector holes, slots, etc) at about 65,000 CUP. If any signs of it happen, you're near the edge of the safety cliff and you better back your charge weight off if safety is any concern whatsoever.

The picture clearly shows signs of it.

Cutting your charge back 2 or 3 grains may be all that's needed. Maybe more. Depends on how much of a safety margin you want.
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  #14  
Old 02-13-2012, 01:41 PM
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Re: excess pressure?

If i dont get at least 5 firings out of brass before the primer pockets open up to much i will back it down till i do.
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