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Seating Depth with regards to powder charge changes?

Discussion in 'Handloading and Reloading' started by DKSDonnie, Jan 10, 2019.

  1. DKSDonnie

    DKSDonnie Member

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    Is there a hardened rule to when you need to start backing down powder charges as you seat bullets deeper or is it trial and error as you seat bullets deeper to look for increase in pressure. I understand that pressure does increase as bullets are seated closer to the lands but as bullets are seated deeper it doesn't raise pressures, as some tend to think, until you reach a point further from the lands that pressure starts to increase just as seating closer does. In fact you may be able to increase powder charge as you seat deeper or vise versa until you find that happy median. I understand that it's a process but was wondering if anyone has found, from experience, a rule of thumb that saves them time esp if you load a certain number of casings and find as you test deeper seatings that pressures start to increase and now you have to tear down casings and reload with lesser powder charges. I'm thinking there is no hardened rule because of the variables when it comes to bullet configuration, hardness of bullets, seating depths, throat dimensions. Thought I would ask. Thanks.
     
  2. ArchAngelCD

    ArchAngelCD Member

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    Seating a bullet deeper into the case will reduce the case volume and will always result in higher pressures. The deeper you seat the less volume in the case which has to increase pressure. That increase however is not liniar. The amount of increase is effected but how large the case is. Small changes in a case as small as a 9mm can increase pressures greatly while small changes in a 300 RUM case, not so much.

    I'm not so sure seating closer to the lands increases pressures all that much. When the bullet is into the lands it will of course. I'm sure I will be corrected quickly if that is incorrect.
     
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  3. DKSDonnie

    DKSDonnie Member

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    I read an article about hardness of bullets that explains it's like pulling your vehicle right up against a curb versus backing off from a curb say a few feet. It takes more throttle/power to jump the curb versus if you start further back, you can sustain a given amount of power to jump the curb and continue on. Kind of an interesting way of thinking about it. Relates to pressure spikes versus a more even pressure curve. I have found that a bullet that's harder/bonded like an Accubond versus a cup&core bullet like a Sierra need more of a jump to perform better. I realize that yes, pressures will increase as you seat deeper but it doesn't happen right away. Every combo has a different place at which pressure jumps either closer to the lands or further from the lands. I have read where more than not, seating closer almost always makes pressures increase faster than seating deeper. Hence the relation between the closer/farther seating example I used.
     
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  4. ArchAngelCD

    ArchAngelCD Member

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    I don't know what you read or where you read it but is eating the bullet deeper into the case will decreasing the case capacity and raise pressures, physics can't be fooled.I

    I can't discuss something you read on the net that I didn't read.
     
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  5. fxvr5

    fxvr5 Member

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    Rifle and pistol cases act a little differently, from what I understand, due to their differences in volume.

    With rifle rounds, you can reduce pressure a bit as the bullet is seated deeper until at some point case capacity is reduced enough that pressure will start to increase. Hornady explains some of the rifle stuff here: https://www.hornady.com/team-hornady/ballistic-calculators/ballistic-resources/internal-ballistics

    Handgun cases, with their much smaller volume, almost always show higher pressure as the bullet is seated deeper. Check out (their) page 3 on this document by Ramshot that looks at overall length and pressure in the 9mm and 40 S&W. http://www.castpics.net/LoadData/Freebies/RM/Ramshot/Ramshot_3.pdf
     
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  6. Bfh_auto

    Bfh_auto Member

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    You might want to read the links that fxvr shared.
     
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  7. ArchAngelCD

    ArchAngelCD Member

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    What did I say that was incorrect and corrected in those links? (serious question)
     
  8. edwardware

    edwardware Member

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    In summary, No. @fxvr5 explained why quite well.
     
  9. Bfh_auto

    Bfh_auto Member

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    Sorry I didn't realize the Hornady one linked so far out.
    Their manual among others says reloading in large cartridges like Weatherby or the Ultra-mag ones, increasing COAL causes pressure spikes because the bullet needs to get a running start to keep pressures down.
    In smaller cartridges, what you said is correct. As size goes up and burn speed of powder goes down it switches though.
     
  10. ATLDave

    ATLDave Member

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    There was also an article in Handloader magazine a couple of years ago about some bottleneck cartridges having a little bit different of a dynamic than straight-walled cartridges in terms of length/depth and pressures. Bottleneck cases, particularly the big ones, are just a little odd and not quite as intuitive as the straight-walled pistol stuff! Unfortunately, I have looked and cannot find the article.
     
  11. Riccochet

    Riccochet Member

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    There is a good explanation in the Lee manual, chapter 9.
     
  12. Slamfire

    Slamfire Member

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    I am sure that pushing a bullet deep does increase pressures, but you know, I think differences in chambers and barrels create more pressure issues. Just his week, took my JC Higgins M50 and my Ruger #1 out to the range. Both are 30-06 rifles. I set up the ammunition OAL based on chamber measurements in the J.C. Higgins M50 which was about 3.280". The Ruger OAL was around 3.33" with the same bullet. At the range, velocity with the JC Higgins, 24" barrel, was just at 2800 fps, with the load below, and that should not be a maximum. But it was. Every round fired blew its primer and expanded the primer pocket. Those primers that did not fall out in the action, I could tap out on the bench.

    The exact same ammunition in the Ruger, shot great. No pressure problems what so ever. Velocity was a little faster, but then, the Ruger has two more inches of barrel.


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    Same load, different cases, no problem in my Sako, I would say, based on velocity, not enough difference to make any claims of pressure differences.

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    So while seating depth undoubtedly does something, differences between rifles probably creates more pressure problems than small differences in seating depth. But I have not quantified the value.

    I have had some zinger 9mm loads. The bullets were severely jammed in the case, like, half or more, due to jams on the feed ramp. Of course, I chambered the things and fired them, and my ballistics really improved! If my memory is correct, the bullet picked up about 200 fps of velocity and about ten more feet of ejection distance! Zing!
     
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  13. Blue68f100

    Blue68f100 Member

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    I noticed your using different mfg of brass for your testing. I would bet the volume is not the same between them from what you experienced. Different volume in the case will drive you nuts if your trying to compare loads. Would require a separate workup.
     
  14. Slamfire

    Slamfire Member

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    It could have. It is hard to know, I did not weigh the cases, and I will agree, that 59 grs of AA4350 is pushing things. Even though, 2800 fps with a 150 gr bullet in a 30-06 ought not be in the red zone. If I was getting 2900 fps or more, (which incidentally is what commercial Federal 150 grain ammunition clocks at) I would be much more suspicious about pressures. Clearly I am going to have to cut the load for my JC Higgins, but the load works fine in two out of three rifles, and to add a fourth:

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    no problem there. The JC Higgins has a chrome lined barrel and that may be the difference. That barrel was so fouled, when I purchased the rifle, I could not see the rifling. It was however, an FN Mauser action, and I wanted it. I love Mauser actions

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    I soon found the HIggins barrel fouled in less than 20 rounds. I took the rifle to a gunsmith who "honed" the barrel. He literally said honed, but I did not get to see what they did. Whatever he did, it took many more rounds before fouling appeared, but appear it would as dark spots in the barrel and you could feel a constriction with a bristle brush.

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    from a CMP Talladega shooting session

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    When was the last time you paid $8.43 for 20 rounds of Federal 30-06?

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    However, I used something that totally made the fouling go away: greased bullets. I must have fired over forty shots on Monday with that rifle and I greased the heck out of my bullets. I had plumes of grease in the air! I could see them waft away in the early morning breeze. And you know, after pushing a patch through the barrel, and looking through the tube, it was shiny bright and clean. I did not feel any tight spots with a bristle brush either. Too bad I tossed out about ten 30-06 cases with expanded case heads.
     
  15. bikemutt

    bikemutt Member

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    If you want an answer to your question you may want to consider acquiring QuickLoad software. I've found it to track remarkably well with measured results in the field. Having said that, "the field" doesn't include a pressure barrel intended to measure pressure, I'm talking about measured velocity using a suitable chronograph.

    As far as seating closer to the lands increasing pressure, I don't think that's the case until you jam a bullet into the lands to one degree or another. There's an inexpensive way to know how deep to seat bullets before jamming them; Hornady sells their Lock-n-Load OAL gauge which, along with a prepared case for your cartridge of choice, will get you close enough.

    My experience is entirely with bottle neck rifle cartridges.

    Regardless, there is one hard and fast rule that's worth adopting if you handload; start low, work up.
     
  16. Riccochet

    Riccochet Member

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    The Hornady OAL gauge works, so long as you can work past it's nuances with their provided cases. For instance, the case they provide may not depict the actual measurements of your barrels chamber. Since the gauge slides in and rests against the shoulder the actual case head to shoulder measurement of a fired case compared to the case provided by Hornady can be off by a few hundreds. Without something like a headspace comparator to know the difference you could potentially be incorrectly calculating minimum seating depth.

    They also sell a kit to drill and tap a once fired case to use with the OAL gauge. That would be ideal over using one of their provided cases. At least then it will provide accurate measurements.

    I've also done the cut neck method on a once fired case that I only neck sized. It provides similar results to the Hornady OAL gauge, as long as you are careful during the extraction.
     
  17. bikemutt

    bikemutt Member

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    You are correct of course.

    For example, with one particular setup I have, the Hornady OAL gauge compared to an actual piece of fire-formed brass reveals a 0.006" difference, so I adjust for that.

    Hornady recommends, IIRC, 0.020 to 0.040 for bullet jump. My guess is if a person follows Hornady's recommendation it should keep them out of the seating depth weeds; that is, no jam. Beyond that, it's just a data point from which to begin.
     
    Last edited: Jan 12, 2019
  18. Archie

    Archie Member

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    The smaller the powder space (the volume in the case PRIOR to the round being fired) the greater the pressure. As someone mentioned, the pressure increase is not linear in relation to the powder charge. (I do believe Boyles' Laws have a bearing).

    Then some entity talks about pressure increasing when the bullet is seated further out. But what is happening is a different function than chamber volume. When the bullet begins to touch or engrave on the rifling, the initial movement of the bullet will be delayed and pressure increases. However, this does not reflect on chamber size, but on resistance to movement.
    By the way, this resistance to movement can also be affected by tightness of neck sizing, or by crimping.
    Some will then conclude seating bullets out to the lands is a 'bad thing' as it changes the pressure curve. It is and it need not be.
    If one starts at minimum loads and works up, one will note two things. The velocities at all load levels are increased, and one observes a lower 'maximum' loading. But with observation, one does not run recklessly into over pressures. All the loading manuals warn to begin the work up again when changing any components or factors. No kidding.

    I find the bullet against rifling technique also encourages a better powder burn, giving more consistent results. However, I use and recommend such a technique only with either high accuracy equipment or single shot rifles or for use in only one rifle. A cartridge loaded to engage rifling in 'this' rifle may not even chamber in 'that' rifle. They may set next to each other on your rifle rack.

    As mentioned, different manufactured cases will have different powder capacities.
     
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  19. Llama Bob

    Llama Bob Member

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    As a starting point. calculate the amount of space your setback consumes in grains H20. For every grain H20 of powder space lost, remove 1 grain of powder. Since the density of most powders is roughly the same as water, you'll be keeping your loading ratio about the same. This only works for small changes.
     
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