WLP primers used up to 49K psi

Discussion in '10mm Reloading Forum' started by preventec47, Mar 27, 2012.

  1. I was talking about the relevance of reading primers in another thread and found that the .475 Linebaugh uses
    WLP primers at max pressure of 49K psi in the latest ACCURATE load data. I am still perplexed at how
    we are supposed to read primers for signs of pressure.
    If I was using WLP primers, unless I have a head space
    issue, I think these primer pressure signs would be indicating mid 50s K psi.? ? ?

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  2. Taterhead

    Taterhead Counting Beans

    You are exactly right. Any loading manual will explain that reading primers is fairly dubious for predicting pressures. Flattened primers can be indicative of heavy pressures, but can also result from unrelated causes.

    I see posts where guys seem to use this as the single indicator of load safety. "Primers look round so I will keep working up..."

  3. yep! It's also my understanding that primers are a bad indicator of pressures. in pistols particularly.
  4. In general I agree, but I still do look to the primers for feedback with what is going on.

    How useful the primer might be to me depends a lot on the caliber, gun, the brand of primer, the powder, etc. For instance, if I am shooting my Model 29 with Federal primers and AA#9, I don't bother to look because I know they look like fish scales, regardless of the load.

    On the other hand, I have a couple of 9mm guns that I shoot some particularly hot loads out of and with Winchester primers and a couple of the VV powders I like to load, I can tell when I have entered the twilight zone, just by what is going on with the primers.

    I think to some degree the value of the information available by looking at the primer is an experience thing. By that I don't mean how much reloading experience you have per se, but experience specific to all the ingredients of a given load and the gun you are using it in, and then it is more of knowing when it will give you some good feedback and when it is not going to tell you anything.

    Of course, then again, it could all just be one big misconception on my part, it wouldn't be the first time for me and things that go bang. :whistling:
  5. Hmm, that would be me...:)

    I don't think they can tell me exact pressure, but haven't seen a 36K PS I load that didn't flatten the primer some, at least in the stuff I shoot. That being the case, if the primer is still round, I doubt the pressure is very high. The primer can be flat without high pressure, but I don't think it can stay round at high pressure.

    I shoot few factory loads, but most of them flatten the primer some as well, so I don't think you have to get to 50kpsi to see pressure signs w/ pistol primers. Not saying it is an ideal way to check pressure, just that in some guns it can tell you something(though I can't say for sure exactly what that is...).
  6. 1st in a polite way, I'd like to know why you think you have
    seen a 36K psi load. Are you saying your load recipe
    was indicated in a load data table and they said it was
    36K ?
    2nd- if you are seeing all those signs, I think you have
    a head space problem where the case moves forward
    when firing pin hits then case expands and pushes the
    primer out a bit and then pressure pushes the case back
    and deforms the primer.
    Like I said, how can we be seeing primer deformation
    at mid 30 Ks pressures when they are prescribed for
    other 49K psi ammo ?

    This is the whole reason I wanted to try to get four other guys
    together who wanted to pressure test their ammo choice
    at a certifired pressure testing lab that ammo suppliers
    to the military use.
  7. I don't believe everything I read on the internet, nor do I think every gun writer is infallible, but when I see writers like Charles Petty repeatedly suggest that by the time you see a flattened primer you may be at 70,000 psi, I do have to at least file that away in the old memory bank.

    You Can Learn A Lot FROM A PRIMER

    The MYTH Of Flat Primers

    Or noted gunsmith John Linebaugh:

    "Straight cases handle pressure differently than bottle-neck cartridges and often show no excessive pressure signs. We have blown a few guns up here, on purpose, and in all instances upon recovery of the cylinder fragments and case remains, the primer has shown normal pressure. Pressures in these instances have run from 70,000 to over 100,000 psi in our estimation. Do not depend on case pressure signs for danger signs in a sixgun. In most cases the first sign of high pressure you will have, other than excessive recoil and blast, is a bulged cylinder or cracked bolt notch."

    A flattened primer can simply mean the primer pocket was loose, or a smaller diameter primer was used in a larger primer pocket.

    Having said all that, yeah, I still look at my brass, particularly if I am working up a load in virgin Starline with Federal primers, because I'm very familiar with that combination, and can make some very rough judgements with it, having been first informed by book values and QuickLoad. My father-in-law has been loading for 60 years, and he indicated that he places little faith in reading brass, except for large issues, like "this gun will blow up if I shoot this round many times".
  8. Alright, here are the reasons for my biases. Pictured below are two pieces of brass, one from a recent load w/ 7g of 7625 under a 240g bullet, the other is most likely 22g of H110 under a 300g bullet. The gun does not seem to have any issues, and shoots well. I have other primers that read similarly with the same loads.


    I see similar progression of primers in other loads as well, so at this point stand by the statement that a primer will go flat under a lower pressure than 49Kpsi. Realistically, it is probably a function of pressure AND time, so it could very well be that a fast powder (shorter pressure curve) or a shorter barrel (less time under pressure) may not show signs as quickly.

    Here are a couple more... The first set is a 218g bullet @ 1100, this load did not smile in a factory G20 barrel, so I am assuming the pressure is somewhat reasonable. The second is a 225g @ 1200, this one showed a noticeable smile in the factory barrel. Though this particular piece of brass was shot in a different barrel, the primers look the same. This one is well over SAAMI max. Notice the difference?


    #8 Any Cal., Mar 28, 2012
    Last edited: Mar 28, 2012
  9. The first article says primers start falling out as pressure approaches 70Kpsi in a particular rifle. OK, primers falling out are bad. Of course, in the specific case mentioned, it is a fairly mild overpressure situation...

    The second says that "marked" flattening CAN mean pressures over maximum have been reached. A rather vague statement, but basically severely flattened primers can be bad. I think everyone already understood that.

    John Linebaugh's quote is worthless. Look at the 3 pics I posted. I am seeing a variety of pressure signs in the primers, and no blown up guns. According to him, he blew up guns and the primers looked normal? I seriously doubt that is possible.

    I don't have any issue with you, or your position, but rather the articles themselves.
    #9 Any Cal., Mar 28, 2012
    Last edited: Mar 28, 2012
  10. There's plenty of room for honorable gentlemen to disagree in a civil fashion. To clear and honest, despite what those articles say, I have on more than one occasion seen progressive change in primer flattening, then flow, and finally headstamp obiteration and a black ring around the primer in virgin 10mm Starline ladders that I am reasonably certain stopped below 40,000 psi. Indeed, I have such cases in front of me, still labelled in baggies. Starline brass is soft, I believe, and as Clark has noted, the LPP in 10mm weakens the case base compared to 40S&W with its SPP.

    The point I was trying, perhaps too hard, to make is that there are various methods of estimating overpressure conditions. I choose to use them all, because none is perfect in all situations. When I'm on the line, I typically do not have micrometers to use the Waters Method or a PC to run QuickLoad (which I always run before loading), so I tend to look at brass (for nicks, extractor marks, shiny spots, and fading headstamps) and primers (for flattening, flow, and black rings). Any of these methods has limitations (including QuickLoad), but I do not have to choose just one, I can use them all. Since it's my gun, hand, and maybe face at stake, it's not too much trouble. Hopefully I shoot more rounds for practice than doing load development anyway (although that has not been the case lately, as my recent freehand marksmanship indicates).

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