Overpressure Signs ?

Discussion in 'Reloading' started by Nvhunter, Sep 15, 2008.

  1. Nvhunter

    Nvhunter Well-Known Member

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    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.
     

  2. AJ Peacock

    AJ Peacock Well-Known Member

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    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
     

  3. eddybo

    eddybo Well-Known Member

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    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.
     
  4. royinidaho

    royinidaho Writers Guild

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    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.:rolleyes:
     
  5. davewilson

    davewilson Well-Known Member

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    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.
     
  6. Clark

    Clark Well-Known Member

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    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: Sep 21, 2008
  7. seidersjoden

    seidersjoden Well-Known Member

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    I have a 30-378 Weatherby. This was shot with 110.5g of 50 BMG with 230g Berger TGT Hybrid bullets. The primers have craters but there are very light to no markings of the extractor and the bolt wasn't sticky. Is this acceptable or not?
     

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  8. Gunpoor

    Gunpoor Well-Known Member

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    I have only pushed one rifle to the point of seeing over-pressure indicators (plural). A little cratering can be a sign of too much chamber pressure but by itself doesn't even get my attention, what really gets me to sit up and take notice is a shiny case head and sticky extraction. When you have these you are on the very threshold of DANGER. As I said before I pushed one rifle to this pressure point and I was about 2 grains over max published load in the manual I was using. BTW, I saw the primers starting progressively getting flatter as I shot increased charges.

    I don't consider a chronograph a very reliable machine to measure chamber pressure, though I am sure I am in the minority. I have and have had rifles that if I were to push them to the published velocity could very well have had a kaboom. There are too many variables and variations in barrels that contribute to velocity.
     
  9. mustang58

    mustang58 Well-Known Member

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    Many signs of pressure have been mentioned. I watch the above along with checking the web. If it expands .002 in my opinion it is time to back off a little.
     
  10. seidersjoden

    seidersjoden Well-Known Member

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    If what expands, case diameter, neck diameter, or length?
     
  11. Barrelnut

    Barrelnut Well-Known Member

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    They explain this in detail, and how to measure it, in the Hornady reloaders guide. Not trying to be rude, but it is highly recommended to read the standard reloading bibles and then ask questions about what is not understood or that you disagree with. You will be more knowledgeable and safer in the end. Probably more accurate too. :)
     
  12. seidersjoden

    seidersjoden Well-Known Member

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    Although your not trying to be rude, you were by assuming I haven't read reloading manuals, just finished the Berger one last weekend. Lets see if you like your own medicine: Not trying to be rude but it's highly unlikely you have the experience and background that I possess. That being said I normally don't say that to others being that is simply not humble and a very assuming thing to say. Back to gun stuff, I know of the signs of overpressure but I wanted to get peoples opinions, reloading manuals always error on the safe side and forums can't always be trusted, I like to find a middle ground. Now why don't you play friendly and be a mature adult and tell me what the Hornady manual says, since again, you assume I have a Hornady manual; after all, this is why were on forums, to talk.

    Joden
     
  13. seidersjoden

    seidersjoden Well-Known Member

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    Were you 2.0g or .2g?

    So far with 50BMG and Retumbo I have found I can go over 2.0g-4.0g and maintain safe pressure, that 115g and 101g of powder respectfully.

    Thanks
    Joden
     
  14. Kennibear

    Kennibear Well-Known Member

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    Reading pressure signs from cases and primers is somewhat of the black arts. If you load long enough you get a feel for high pressure. I personally feel if the bolt handle starts binding you are probably too hot. One of my tests using a bolt action is to point the muzzle straight up after firing and unlock the bolt. Without pulling back even the slightest amount I release the bolt handle and see if the bolt will extract the case fall from it's own weight.
    Yes, I know there are variables even with this to include chamber dry or lubed, FL sized cases or neck only, etc. But my reasoning is:
    The force to extract is pretty consistent compared to my subjective "feel".
    If the case is binding enough to resist the bolt's weight then I should check things out.
    If I am hunting I want the gun to work no matter what, etc.

    I do not measure case head expansion because of the great variation of brass hardness between makers and, in some instances, differing lots from the same maker. That being said, too much head expansion across the web is bad ju ju. If I find it I back the load down.

    I have always read primers because they have been the first thing to let go. A system fails at the weakest link and overloads have always hammered the primer first for me.
    cropped primer.jpg
    In the photo above are two Federal #215 primers that are known to have hard and thick cups. If the #215 is showing pressure you got issues. The left is an unfired primer seated in a 375 Ruger case. Two things to notice:
    1) The radius at the perimeter of the primer is pronounced. That is, it is a larger radius than the other fired primer.
    2) you can make out the seating punch indent in the surface. Primer surface condition can tell you a lot, including how rough the machining is on the bolt face. These primers measure 0.210" to the nearest 0.0005".
    The right primer is from a 300 WinMag load of 150gr TTSX/ 79gr RL 19/ Fed #215/ 3.500" COAL. Velocity = 3349fps, SD= 9fps.
    If you click on the photo and look at the radius of the outer edge of the primer it has sharpened up a lot. The slight cratering is from a light firing pin spring because every load in this Rem 700 craters to that amount, even the light development loads. Note the imprint of the bolt face on the primer surface. This gun has a rough bolt face and it makes reading the primer easier because the imprint sharpens up very progressively with increasing pressure. The tool marks are very well defined.

    Back to the primer edge radius. If your head space is pretty tight this only occurs with high pressure. It is progressive. When punched out carefully the primers show a mushroom shape with the diameter at the radius measuring 0.212". 0.002" increase is the max I will allow with the #215. But if the radius forms a sharp 90 degree edge I take that as a touch too much. Usually at that point the bolt will not extract freely when the muzzle is pointed straight up.

    This rifle is equipped with a PT II strain gauge and that load tests to 62Kpsi. The primer appearance is consistent with the "feel" I have developed over a 40+ year reloading career.

    Just my two cents and a picture.

    KB