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How Flat is Too Flat?

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  • How Flat is Too Flat?

    Beginning handloader question:

    My Winchester 30-06 (Model 70) flattens primers. It does it with factory ammo (Winchester Failsafe 180 gr. & Remington Core-Lokt 150 gr.) and it does it with my handloads (Barnes TSX 180 gr. BT). Even with the starting charge of H4831 my primers (CCI 200) lose their rounded backside and develop a bit of a corner. Now that Iíve worked my way up to charges near the max listed loads, Iím noticing sharper corners.

    The Remington factory loads have an initial primer seating depth between .003 and .005Ē. Once fired, the primers sit flush. The Failsafe primers donít back out at all. My handloaded primers occasionally back out to flat, but itís one out of every 5 or 6, and not predictably -- that is to say, none of the primers backed out at a powder charge of 45.5 grains, and one did at 46, but none at 46.5.

    Hereís what Iím not noticing:
    1) Case head expansion. Both factory and handloaded cases range from .463-.4645Ē immediately forward of the extractor groove, which is the same variance I measure with unfired cases.
    2) I donít notice any primers cratering around the dent the firing pin leaves.
    3) I donít notice any shiny spots or cuts in the headstamp area.
    4) The primers aren't totally flat - they're flatter. I don't have a good way to measure how much.
    4) Heck, I donít even see a pressure ring where the case web tapers off.

    Since my rifle just seems to flatten primers, how do I look for signs of excess pressure? The Barnes folks don't have published data for the TSX. They say you can work the TSX up to more than the listed max load for the X bullet by 1 or 2 full grains if you're careful. I aim to try, as long as the groups stay tight, but I need to figure out what my warning signs really are.

    Or am I missing something important here?

    Appreciate any insights...

  • #2
    Flattened primers

    Just the fact that your primers look flatter then before firing doesn't necessarily mean there is excess pressure. This is a common occurence. Case head expansion is a more important factor and judging from what you tell us, it is not excessive. Can you still detect a slight groove between the primer and the edge of the primer pocket? If the primer is spread right to the very edge of the pocket, that might indicate high(er) pressures then normal. Does the firing pin dent in the primer show some extruded material above the surface of the primer cup? Are the letters on the base of the case "smeared" looking? If not, then you're okay. I have been using Winchester primers for many years because their primer cups are a little softer, so signs of high pressure show a little sooner, giving you a bit of an edge before maxed out pressures are reached. I don't know if the new copper colored Win primers will be the same. I have also noticed differences in primer pocket diameter and the amount of pressure needed to seat primers, which may be a factor. You are being careful and following the proper methods for detecting pressure, for which I commend you. Hope this helps.


    • #3
      As Mauserboy said, if the primer has really expanded to fill the primer pocket things are getting warm. The primer pocket will also loosen up on a really hot one and the primer might fall out. If you have a push feed model 70 you might get a mark where the case head has flowed back into the ejecetor cut. You could also get sticky bolt lift or extraction. Slightly flattened primers and/or cratered firing pin impressions on the primer are not always signs of pressure that is too high.


      • #4
        Flattened Out...


        I like your appraoch, you're doing it right. I have always liked Ken Waters case head expansion measurement for pressure refference.

        A flat primer is a sign of high pressure, not excess pressure. Each rifle will treat primers slightly different. When excess pressure shows up on a primer it makes what I call a top hat. If you punch the primer out, the bottom, the closed end, will have a raised rim all around making it look like the brim of a hat. Normal primers will have this also and as you change brass, different brand or different lot, the size of the "hat brim' will change. I expect to see this on any primer from a high pressure rifle cartridge. (30-06)

        A cratered primer, is when the primer cup craters up around the firing pin detent. Some rifles with an oversized firing pin hole in the bolt face will always do this, and some soft primer cups will always do this in any rifle. But if it doesn't do it with factory loads, it wouldn't be expected to do it with handloads.

        Your flat primers that are not getting pushed back flush with the case head are lower than normal pressure. A normal load will flatten the primer and slightly make a top hat rim on the primer. This is about 54-56,000 psi.

        EXCESS pressure is when the top hat is flowing. We can tell by the appearance of it being slightly out of round or one side of the hat brim is sticking out more than the other. That is too high probably about 65,000+ psi.

        Now, here is a caveat. None of these symptoms can be trusted until the brass has been fired in the rifle at least once. The brass must perfectly headspace before we can use the primers for reference. It sounds as though your brass isn't headspaced to the chamber yet and/or it is a very mild load.

        Brass head distortion from ejector/extractor cut out or other bolt head marks is excessive pressure for any caliber and any "normal" rifle bolt.

        If you want to use the case head expansion as a gauge, compare factory loads, (standard, not HE or Light Magnum) with handloads and when head expansion is no more than .0010" greater than factory, you're there. (Do not use nickeled cases for this.) This is one firing. In other words measure ten factory cases to get an average after they're fired then use new brass of same brand, (Winchester Ammo and Winchester new brass) then load five cases of you test load and shoot and measure. If they average .0010" greater diameter, you're at max pressure. If any one case is .0010" greater you should back off.

        Your load of 46.5 grains of H4831 is very mild. Your cases are not expanding at all. Your load should be 56.5 grains, am I reading this right? I use more of a faster powder and have very "normal loads. Do you have a book that shows a charge of 46 grains of H4831 for a 180 grain bullet? That doesn't fit with my 60,000+ rounds of 30-06 ammo experience. I would say this load borders on the "don't do, because it's too light" category with slow burning powders.

        You have good technique and are very cautious, that's a good thing. You need a chronograph, you're much too scientific to be satisfied with out one.

        The others are giving you good advice, I'm just longer winded. I hope this helps. Good shootin'.

        Last edited by Murphy; 07-11-2006, 14:11.
        Is there nothing so sacred on this earth that you aren't willing to kill or die for?


        • #5
          More cautious... TYPING.

          So much for careful and methodical... Yes, Murphy, those charges should have been 55.5-56.5 grains of H4831.

          It sounds like I oughtn't worry about these flatter primers yet. They certainly haven't filled the entire primer pocket - there's some way to go before that happens.

          But I'm nervous about waiting for case head expansion. Especially since all the fired cases have come out of my rifle with case heads measuring under .465". The cartridge drawings in my manuals and online show that dimension at .470" for the 30-06 Springfield. I ain't waiting for .005" (or more!) of expansion to stop adding powder. So I'll measure before and after. Do I need to be concerned that cases emerge from my rifle with a smaller head diameter than spec? Factory ammo chambers just fine, so the only downside is that I might have trouble chambering somebody else's handloads, right?

          So I'll bring my calipers to the range next time. But I'm intrigued by the notion that I oughtn't rely on pressure signs like these until I'm working with once-fired cases. My load development to-date has been with a batch of brand-new brass - all sized, trimmed, and otherwise treated uniformly. Are you saying it isn't enough to set the full-length sizing die based on a factory case that was fired in my rifle? I really need to be using once-fired brass?

          If that's the case, I'll do the rest of my load development with the cases I've fired so far - but I guess I don't get why. Didn't the full-length sizing die ensure headspace and cartridge dimensions comparable to a once-fired case?


          • #6
            loads, pressure

            Kudos to your technique! It's the right approach. However, don't be lured into trying to get every last fps out of your loads by the "velocity is everything" thing. Listen to Murphy about the head expansion. If you're getting "undersized" head measurements after firing- that just means your pressure isn't great enough to fully expand the STRONGEST part of the case out to your chamber dimension. Additionally, after firing, brass will have a .001-.002 "spring back". If you were to shoot a round where the case COMPLETELY filled the chamber, clear to the rim, to the last .0001-.0005 of an inch and the measurement, after firing showed that, you may be way over-pressure- even though the reference books show that as nominal chamber or cartridge dimension. All chambers (and many cartridges from different sources for that matter) will have slightly different dimensions, including the back (head) portion. The best reference for this dimension, as others said, is the factory-fired round in your chamber. It's one of the best comparisons for your reloads- the factories go to great lengths to assure safe, dependable loads. Also, one caution about under-loads. An under-load, at some point less than the recommended starting load, especially with slow ball powder like 4831 can have bad consequences.
            -Good reloading, shooting-


            • #7
              Learnin' the ropes...


              I think there are couple of areas where I misled you, so I'll try to clear that up.

              But first, The base diameter of the 30-06 case is .470". That is the maximum dimension allowed by SAMMI specs for the case. And, that's because the Minimum SAAMI spec for the 30-06 chamber is .470". or there abouts, but any way, don't matter the exact numbers. So new brass will always be less than .470" to insure it will fit all 30-06 chambers. Of course all dimensions of the chamber and brass have a minimum and a maximum to insure a "fit". One of these dimensions is the headspace. Here again all new brass must fit all chambers so brass must be minimum. When the brass is first fired it is under the ideal headspace for your rifle, but will stretch to fill the void, and now it fits. When we run it through the full length sizing die, we set back the shoulder to the new brass, minimum headspace dimension, guaranteed to fit all chambers. So, full length sizing is not the best for the handloader, because we would gain nothing from the constant misfit and the brass stretches each firing and doesn't last as long. The best is neck sizing with ocasional partial full length sizing or use of a body die.

              The important thing is when you resize do not set the shoulder back as that changes the headspace dimension. If using the F/L die, back it off so it doesn't touch the shoulder. You will see a sizing ring in the neck lube and just screw the die in until it sizes the neck only then lock it in that position. It will still size the base all that is needed to chamber easily. If you size this way after the first firing the case has expanded to all the critical dimensions and will not change in subsquent firings, (unless over pressure). Also the brass will not need to be trimmed as often as stretching is all but eliminated.

              That's what I mean by once fired. Now as to your measurements. You'll need an actual Micrometer, a Caliper won't measure accurately the the fourth place. They are only accurate to .001" even though we can see the needle half way between the 3 and the 4, that doesn't mean .0035".

              Now, when I said case expansion, that means .001" more than factory expansion. Expansion is how much the case increased in size during the firing. If a case measures .4650" before firing and .4658" after firing that is eight ten thousandths. (.0008") A case will likely never get to .470". Compare the before and after measurement of factory ammo and the before and after measurement of your first fired handloads. The amount of increase in case diameter at the webb, just forward of the extractor slot, is what we are looking for. You want no more than .0010" expansion over the factory load expansion. You can, however, get by quite well without this measurement by looking at the primers and case head after firing. Your question about head diameter less after firing, this is normal for a mild, case forming (fire forming) loads and indicates the case is growing length wise and not in diameter, add some powder. You have to see it to learn about it.

              Also, another quick look pressure sign which is useful on some guns is the texture of the boltface around the firing pin hole, the part that the primer will expand against. If it is a little rough with minute milling marks these will transfer to the primer. It is sort of a cross hatch pattern, this is the look I want on my fired primers. The pressure will vary with the brand of primers, but is about 55,000-60,000 psi. The brass won't show it, just the primer, and that's good. This is where we want to be.

              The 30-06 will send a 180 grain, copper jacketed lead bullet out at 2750 fps with this pressure, when fired in a barrel of correct dimensions. Copper won't get there as the friction is much higher, but that is the norm. Back to your powder charge, You cannot get enough H4831 in a 30-06 case, with a 180 grain bullet, to give a over max or even max charge. You really need RL-19 or H4350 for best performance. Yes you can use up what you have, it will work fine, just a little slow. I have 24 pages written on "recognizing pressures" for a book of mine and each time I read it I add something to it. It is a comples subject and has many variables. It takes a lot of looking at primers and case heads to know what is good, bad or ugly. Good shootin'.

              Last edited by Murphy; 07-11-2006, 14:12.
              Is there nothing so sacred on this earth that you aren't willing to kill or die for?


              • #8
                re: 4831

                Oops! 4831 is an extruded powder- not a ball powder. Had recently worked up a load with H414, a ball powder, for an -06. Anywho, the caution about gross under-loads of slow powders like 4831 still applies.


                • #9
                  Going on the wish list

                  A chronograph is definitely going on my wishlist.

                  That said, I see what you mean about H4831 and max pressure loads. The Lyman manual shows it under 50,000 psi, and that's as high as any Lyman manual load ever goes for the '06.

                  My other manual is M.L. McPherson (3d ed.), and he doesn't balk at listing 60,000 psi loads for the '06. Although he gets less velocity out of those than he does from several slower-burning powders with 180 grain projectiles.

                  Both manuals list H4831 below 50,000 psi at a max load, and getting higher muzzle velocities than some of the 4350s - lower MV than others.

                  Loading the all-copper triple-shocks without a printed manual of proven loads might not have been the best choice for a first timer, but I'm having fun with it. And the loads print some darn fine groups at 100m. When I get 'em worked up as high as I'll go, I'll see how far they drop at 300. That should let me back into some rough idea of muzzle velocity based on the ballistic tables, no?

                  Apropos of nothing anybody's said here, the Triple-Shocks have given me only one real cause for complaint. The seater plug on my RCBS die grabs them. It cuts a little ring around the ogive and, with compressed loads, it doesn't want to leave the bullet in the case. It seats 'em and pulls 'em, all with one run of the handle. I've already sent off to RCBS for a custom seater plug. Hope they hurry, opening day for goats is coming fast!

                  Thanks for all the help, gents. I appreciate it a very great deal.


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