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Overpressure Signs ?

 
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  #1  
Old 09-15-2008, 10:28 AM
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Overpressure Signs ?

I have been reloading for quite some time. I have always produced loads that were in the lower 50% range relating to powder charges and have chosen mid grain bullet weights for any given caliber.

Lower power loads have contributed to a long life of my armory. I have a need to push my 30.06 for the up-comming season. Published grain charges for 30.06 w/ 165 spitzer point, H414 are from 50 grains to 56.5 grains. I will be reloading the higher end of these charges - 54, 55 grains.

My question, What are the signs of overpressure when loading high power for a non belted cartridge. I have read books on the matter, but think I may gain a better perspective of what to watch from the group.

Thanks for your input.
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Old 09-15-2008, 12:38 PM
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Re: Overpressure Signs ?

Some reloaders measure the cartridge and watch for excessive stretching. This has been statistically shown NOT to be a good indicator of pressure. It is more an indicator of brass alloy and how much the brass has been worked in the past.

Others will point to primer pockets opening, same issues as above.

Some will watch for ejector marks and load ammo that is below that level.

The amount of flattening and cratering of primers has been pointed to as a good pressure indicator (even though it can really be a sign of other things, like firing pin spring strength, primer softness, firing pin hole clearance and headspace issues).

All of the above 'CAN' be signs of pressure and they should ALL be watched.

In my opinion, the best thing you can do is shoot your loads over a chronograph. Do some research and get an idea of the velocity you should get for your '06, barrel length and powder. Then you will know where you are on the pressure/velocity spectrum for your combo of components.

Hope that helps,
AJ
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Old 09-15-2008, 02:39 PM
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Re: Overpressure Signs ?

Yup, I would say get a chronograph, pick a velocity and work your way up watching for the traditional pressure signs. I think in some instances such as case expansion and cratering that the signs may not tell you anything except that you have a gun problem. I have seen instances where factory guns will have terrible looking cratering with even low pressure loads. (bushing the bolt to a smaller firing pin will usually rememdy this)

I do put some stock in primer flatening. I do not think I have ever seen a primer flatten on a low pressure load unless there was some oil in a chamber, nor do I think I have ever seen a high pressure load that did not flatten the primer out to its edges.

I also look for extractor marks and heavy bolt lift, just my 2 cents but I an no expert.
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Old 09-15-2008, 03:26 PM
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Re: Overpressure Signs ?

I've gone through most all of the pressure sign reading. It's pretty much witchcraft.....to me.

I've settled, if I want long case life, which I don't care about any more, I increase powder to the point where the Remington bolt "clicks" on the up lift. Pressure is getting there. Two clicks, the second when arriving at full bolt lift, the pressure is getting really up there.

Finally if I have to hammer the bolt back with my hand, pressure has increased a bit more. If I have to use any sort of "tool" to get the bolt back, I'm in territory that I shouldn't be treading.

All of this is with an alcohol cleaned chamber and brass.

I also use an RSI pressure system which is pretty nifty once calibrated. Which, in my case, from the above descriptions, has probably been a life saver.
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Old 09-16-2008, 01:49 PM
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Re: Overpressure Signs ?

the only true way to tell is if the bolt starts lifting harder. this means that brass is flowing and that's too much pressure. primers are indicators at best for the reasons already mentioned. brass is simply a gasket. when the gasket starts moving it's a red flag. the height the flag is raised are dependant on reasons Roy has explained. my red flag is any change in bolt lift.

i was loading 62 gr of 414 in my 06 using 168 TTXS 's with no change in bolt lift. this is supposed to be a VERY hot charge but the bolt lift will tell you everything you need to know.
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  #6  
Old 09-21-2008, 07:20 AM
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Re: Overpressure Signs ?

I have overloaded to case failure with 22-250, .243, .243Win, 257 Roberts AI, 270, 7x57mm, .308, 30-06, and 8x57mm.

Most of these cartridges have different max pressures ranging from 37kcup to 65kpsi per SAAMI registration in the USA, but they all have the same real pressure limitations in modern strong bolt actions.

These cartridges and many more descended from the 1889 parent cartridge: 7.65x53mm Mauser.

If you are good with Quickload, and change the start pressure from 2,000 psi to 5,000 psi when the bullet is jammed into the lands, then a very accurate velocity and pressure prediction can be made.

The above Mauser case head cartridges, your 30-06 included, will have long brass life [the primer pockets will not get loose] at ~ 62,000 psi.

If you don't mind still bolt lift and loose primer pockets after one firing, you may shoot at 72,000 psi.

If you shoot at 90,000 psi, then the primer will fall out, and you have escaping gas on the bolt face.
I have overloaded lots of ammo until the primer pocket doubled in size, but that is not a useful practice toward practical ammo, other than a lesson in upper safety limits.

The exception to this is the 6mmBR and 6.5x47mm brass that has small rifle primer pockets.
The limitation to pressure with this case head [although shaped like an 1889 Mauser case head, it is much stronger] is the CCI450 magnum small rifle primer piercing. To get higher pressure, the firing pin should be bushed. If the firing pin is .062" and the firing pin hole is .063", then the pressure can go to the next level.

Last edited by Clark; 09-21-2008 at 07:26 AM.
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