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Thread: Primer pressure signs redux

  1. #1
    Member Yukoner's Avatar
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    Default Primer pressure signs redux

    So further to my past queries on excess pressure signs on primers.
    I was up at the range this AM. I had backed off my past load of 53 Gr of RL19 behind a 160 AB to 52 grains, and I observed the following:
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    On the left is a factory 160 Gr. TBT, the next 3 are from my 52 gr RL19, then the last 2 on the right are from 52 gr RL22, 160 Gr AB.
    My feelings on it are that the third from left has some flattening, and the 2 on the right have the same.
    Any thoughts on this?
    Both the RL19 and the 22 loads were shooting fantastically. 1" group with 6 shots. Easy to chamber, easy to unload.
    Now my handloads are loaded longer than standard COAL to fit my chamber better as per the Nosler manual. I wonder if the excess pressures would be resolved by shortening my COAL? The Federal TBT load is actually under COAL, but still shoots very well.
    Thanks again for the sage advice and tips.
    Paul
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  2. #2

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    Quote Originally Posted by Yukoner View Post

    Now my handloads are loaded longer than standard COAL to fit my chamber better as per the Nosler manual. I wonder if the excess pressures would be resolved by shortening my COAL? The Federal TBT load is actually under COAL, but still shoots very well.
    Unless your longer rounds are really jamming the bullet into the lands, I'd expect the reverse to be true: Seating the bullets further out "increases" case capacity and should result in a pressure drop, however slight.

    I see some flattening, but it doesn't look excessive to me. You can still see the original rounded edges, even on the flattest. I'm not quite sure why you'd have so much variation between rounds with the same load, though. That could indicate some wide pressure fluctations with the same load, and I just can't guess what would cause that.

    Do you have access to a chronograph? If the velocity varied quite a bit, and in synch with the differences in the primers, that would explain the primers, but not why the velocity was varying so much.

    Much food for thought.

    Anyone else with more insights or better theories?

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    I've got to get a chronograph. Period.
    Still kind of strange though, especially as all the rounds were grouping fantastically, no wingers.
    I'm being really carefull on my powder loads, trickling it in grain by grain.
    I wonder if slight variations in COAL might account for it?
    Hmmm.
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    How many loads in these cases? Different tension in the primer pockets can allow the primer to move slightly, which sometimes reveals itself as mild primer flattening. In all cases pictured, there is no flattening to be concerned about. When the primer is flat all the way across the primer pocket, and you can't see a rounded edge where it meets the case, then you have pressure signs. If you miss the flattening, the next think you'll notice is the ring around your firing pin strike will appear flattened as well. When that happens, you're a hair away from piercing the primer and making a mess of your rifle.

    When I get a chance I'll have to see what I've got in the "bucket of reloading reminders" that could better illustrate my point.
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    All of the primers look cratered to me, and the third from the left looks somewhat flattened. I think that Brownbear and you are both on track when looking at the COAL as the possible variable contributing to higher pressures (if any). Specifically, if the COAL is so long that the bullet is jammed into the lands when chambering, you will likely have additional pressures when fired. I once blew a primer doing exactly that with a powder charge that was well within spec's. Can you get your hands on a tool to measure your chamber distance to the lands across various bullets? I use a Stoneypoint, which works just fine for me, although some guys don't like them.

    Doc

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    Can't find any of my 6.5x55 brass that very aptly displays a flattened primer (I'm more responsible now, thank you for asking ). I did manage to find a factory comparison between range-fodder and high-velocity pistol ammo though. Notice how much larger the Norma primer appears, even though it is the same size. Both are still rounded on the edges however, the first pic shows how much more bevel there is in the primer of the Federal load than the Norma load. The Federal isn't even close to overpressure with a 180gr hardcast @ 1150fps while the Norma load is smoking a 170gr at 1322fps, and probably right near SAAMI max pressure.

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    And here's a pic of a .338 Win Mag that's approaching book max. Notice the primer is considerably flatter than yours, yet it still has a bit of bevel to the edges. Not much, but some. A truly flattened primer would fill the primer pocket completely, expanding all the way to edge. They also usually display boltface markings. This load is fast, but it's not unsafe, and the primer is normal.

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    All in all, I think your loads are fine, and your primers don't show any sign of overpressure. Get a chrony anyway (it's very useful after you get past the initial disappointment), but you've got no worries with what you're currently loading and shooting in your 280. Unless your 280 is a Sako. If it's a Sako it's unsafe with any load and you should send it to me immediately.
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    Thanks gents.
    Diesel Nut, great shots! Confirms some things I was thinking.
    Doc, I'm definately not right on the lands. I made up a dummy round with fired brass and took the average length of this rifles COAL measured right to the land, then backed off .030" (I believe it was ..030, I'd have to run out to the shop to confirm) as per the Nosler manuals instructions. Maybe thats not far enough? I'll have to shorten the next batch a hair just to see.
    Cheers
    Paul
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    I haven't seen it happen often, but often enough to suggest that another variable might be neck tension. If there's a lot of variation in case wall thickness, you can get variations in pressures like that, and in extreme cases, excessive pressure with an otherwise "normal" load. That's especially true in custom rifles with minimal chambers, some of which are intentionally chambered with minimal neck clearance.

    I got into all sorts of tarnation with one factory rifle over this issue. I necked down a bunch of 7x57 cases to make 6mm Rem cases. All was fine in one rifle, but in the other it produced cases with necks too thick. At least some of them.

    I don't think it's worth the purchase of a tubing micrometer, because there's a work-around. Measure the neck diameter of a few loaded rounds. Since bullet diameter should be constant, you will be more or less measuring neck wall thickness. I've got a Marquart tool for turning down neck walls, but you can get them to fit some case trimmers. Forster maybe?

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    What you describe with the COAL sounds pretty standard, so that seems OK. Looks like the chronograph is your next move...if your curiosity continues with these rounds. You could also deprime the case that you suspect has a slightly flattened primer, and then reprime it to see if the primer seats with little resistence...thus adding support to the hypothesis of a loose primer pocket. When priming with a hand primer you get a feel for it, and I have tossed some cases for that very reason. Good luck with it, Paul.

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    You are still guessing you are indeed experiencing high pressure. You could just have soft brass.

    Stop guessing.
    www.shootingsoftware.com/pressure.htm
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    Like Doc says, whatchewgot is Cratering around the firing pin hole. I don't see the primers flat enough to indicate pressure, but of course, primers don't alway indicate pressure anyways.

    BUT, you are wise to consider Flattened primers. If they flow over to where you can't see the groove around the PP, I'd say, you definitely have excessive pressure. If you decap a fired round, and the primer is bigger around on top, than on the open end, you're getting up there in pressure, too.

    Cratering, may be a sign of excessive pressure too, especially if it's not present with FLs,. I give you a definite maybe, on that.

    Below, is my answer to pretty much the same question that you asked in your other post.
    ************************************************** **************
    "Originally Posted by Yukoner
    Thanks fellows.
    Would loading longer than standard COAL drive pressures up or down with the same weight of bullet and powder?"

    Generally speaking. It would probably result in decreased pressure because, there would be more case capacity for the powder. (If you take a given load and seat the bullets deeper you will increase pressures.)

    If you increased the COAL to where bullet actually touches the lands in the barrel, that will increase pressure, maybe 8,000 psi.

    However pressure varies from round to round, anyway, for various reasons.

    Smitty of the North Walk Slow, and Drink a Lotta Water.
    ********************************************

    It's common, if not always the case, that FLs are shorter in OAL than they need to be, and it's not uncommon for them to be accurate. I haven't fired a huge variety of FLs, but I've never seen a FL that wasn't crimped either.

    So, these two things that are spose to result in increased accuracy, seating close to the lands, and NOT crimping are not present in FLs that are so often quite accurate.

    I acknowledge that I don't have the experience of many of the other posters, when I say this.....

    I usually, seat about .030 off the lands, but I don't worry none if it's MUCH farther. Seating close to the lands is not something I've needed to do to arrive at an accurate load.

    Smitty of the North
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    To be cratering on loads that don't otherwise show high pressure signs, I'm wondering about the firing pin/hole in the bolt face. It's too consistent to be related to excessive pressures I think.

    I don't recall the make/model of your gun, but I'm getting suspicious that we could be barking up the wrong conifer.

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    Quote Originally Posted by BrownBear View Post
    To be cratering on loads that don't otherwise show high pressure signs, I'm wondering about the firing pin/hole in the bolt face. It's too consistent to be related to excessive pressures I think.

    I don't recall the make/model of your gun, but I'm getting suspicious that we could be barking up the wrong conifer.
    Yeah, it looks like cratering on all of'em.

    Smitty of the North
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    Good points Nitro, Smitty and BBear. Since I'm always learning from folks here...

    Can't high pressure manifest itself with cratered primers without associated flattening of the primer bevels? I always thought so. I realize that primer condition, bolt face markings, heavy bolt lift on extraction, etc. are not the best indicators of increased pressures (they are certainly not direct measures), but they're the best indicators for average Joes like us without pressure reading equipment.

    If there is excessive play between the firing pin and the firing pin hole on the bolt face, then it makes sense to me that the primer could crater upon firing to fill the space...but that hypothesis seems like it would take a pretty loose firing pin hole to cause those craters (am I wrong?).

    I'm not arguing guys, just trying to learn more. In my own thinking I'm right back to wanting chrony data.

    Chuck

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    Quote Originally Posted by Doc View Post
    If there is excessive play between the firing pin and the firing pin hole on the bolt face, then it makes sense to me that the primer could crater upon firing to fill the space...but that hypothesis seems like it would take a pretty loose firing pin hole to cause those craters (am I wrong?).
    Could be a poorly machined firing pin hole; in fact that is exactly what I would guess with the information you've given. I'd inspect the hole for machining flaws. I've seen it more than a few times.
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    Quote Originally Posted by 1Cor15:19 View Post
    Could be a poorly machined firing pin hole; in fact that is exactly what I would guess with the information you've given. I'd inspect the hole for machining flaws. I've seen it more than a few times.
    If it was, wouldn't I get the same signs with factory ammo?
    BTW, it is a Rem 700, LSS with 24" barrel.
    Well, if nothing else, its always a good intellectual excercise for many different minds to come together and figure out a problem.
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    Quote Originally Posted by Yukoner View Post
    If it was, wouldn't I get the same signs with factory ammo?
    BTW, it is a Rem 700, LSS with 24" barrel.
    Well, if nothing else, its always a good intellectual excercise for many different minds to come together and figure out a problem.
    Cheers
    Paul
    The nickel case on the left in the first photo seems to show the same cratering, isn't that a FL? Regardless, the cause of cratering could be from several sources: weak firing pin spring, machining snafu in the bolt face, soft primer cups, excessive pressure, etc. A chronograph with RL 19 & 22 will tell a more accurate story. If your loads are under 2900 fps, and I'm suspecting they are, you are under the threshold that will flatten or crater primers from excessive pressure. The 280 SAAMI spec is a maximum pressure of 60,000 PSI and the manuals (Nosler, Barnes, Speer, etc.) are going to be in line with that. Flattened & cratered primers are very unlikely in a properly functioning rifle until 70,000+ PSI. If pressure is the culprit your velocity will indicate the excessive nature of your handloads. Your loads are on the conservative side IMO and I'd seek answers in places other than excessive pressure.
    Foolishness is a moral category, not an intellectual one.

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