Seating Pressure / Neck Tension

Carlos Danger

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    For anyone who's been reloading long enough you know the "feeling" when bullets are seating at a consistent neck tension. You can tell when one case is tighter, or looser, than the others. Maybe this has been going on for sometime, but just today really paid attention to it.

    When seating the bullet, I have the initial pressure to start the bullet into the case. It feels relatively smooth throughout the entire stroke of the pull, but about 80-85% of the time, I feel a VERY slight resistance near the end of the stroke. Anyone experience, or better yet, know what it is I'm feeling?

    I'll give you a brief description of what I'm working with below. Thanks in advance.

    Lapua 6.5 Creed small base die sized brass.
    Barnes Match Burners 145g.
    Necks are deburred in and out and rotationally brushed (to remove oxidation).
    39.6g powder, no compressed loads.
     

    spife7980

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    90% youre either 1) hitting a donut in the brass where thicker shoulder material has migrated up into the neck or 2) your bullets have a pressure ring on their bearing surface where its slightly larger than the rest of the surface.

    When you find one of those cases pull the bullet and section it so that you can verify differences in thickness and put your micrometer on the bullet and see if you can find where they are .0002 larger at some point or another on the bearing surface.

    Edit: didn’t realize you said very slight. It’s probably just normal case variation like 918 said.
     
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    BattleAxe

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    I'd probably first see if a mandrel pass either makes it go away...or not. It will likely take a brass problem off the table.
     

    918v

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    For anyone who's been reloading long enough you know the "feeling" when bullets are seating at a consistent neck tension. You can tell when one case is tighter, or looser, than the others. Maybe this has been going on for sometime, but just today really paid attention to it.

    When seating the bullet, I have the initial pressure to start the bullet into the case. It feels relatively smooth throughout the entire stroke of the pull, but about 80-85% of the time, I feel a VERY slight resistance near the end of the stroke. Anyone experience, or better yet, know what it is I'm feeling?

    I'll give you a brief description of what I'm working with below. Thanks in advance.

    Lapua 6.5 Creed small base die sized brass.
    Barnes Match Burners 145g.
    Necks are deburred in and out and rotationally brushed (to remove oxidation).
    39.6g powder, no compressed loads.

    What you’re feeling is normal
     

    RegionRat

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    Aug 10, 2019
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    Possible that the boat tail to bearing junction on the bullet, is starting to push into the neck to shoulder junction on your case.
    Even without a donut issue, there is a difference in the stiffness of that junction compared to the regular part of the neck.

    Possible the bottom of the bullet, is starting to push on the powder column and spread it out of the way.
    Possible to be a combination of both of these. The load doesn't have to make it all the way into compression if the column just touches and has to spread into available volume.

    If you are willing, you can stop short of the junctions, or then even intentionally push through beyond them.
    Another test is to seat as you are with no primer or charge to see if it is due to the powder column.
     

    918v

    It’s not the primer!
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    donut is forming in EVERY brass, so maybe it is that.

    A slight increase in seating effort as the bullet passes through the neck/shoulder area is not indicative of a donut. It is a normal constriction resulting from forcing the bullet to expand the neck AND the shoulder. When you start the bullet down the neck the bullet expands the neck. As the bullet proceeds deeper and encounters the base of the neck, it now has to expand the shoulder and the neck. This is perfectly normal and to be expected.

    If you anneal the neck and shoulder to be dead soft then you may not feel this when seating bullets because the case is too soft after sizing. But a correctly annealed case will allow you to feel that constriction.
     
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    Feniks Technologies

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    This is where things like amp press shine.

    You can see exactly where seating pressure spikes or drops off. Allowing you to experiment and figure out why.
     

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    salks

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    For me , it was annealing. Not to get into how much or whatever but to be consistant.
     

    ArtOfStalk

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    Hey all, I've recently started annealing my brass after every firing (300 win mag). Seems to be going well except for the decrease in the tension holding the bullet in the neck. Accuracy is pretty consistent. The trouble is when these loads are put into a hunting rifle's stock magazine. Upon firing, the rounds in the mag slam into the front of the mag well and push the bullets in further. I'm guessing a smaller neck die is in order.

    I have noticed that when seating the bullets there is the initial higher press pressure to get the bullet started but after the boat-tail/shank junction starts in the neck it's smooth sailing. Smooth until the boat-tail/shank junction passes through the neck/shoulder junction in the brass then the amount of press pressure drops significantly.

    A kinetic puller only needs about two moderate whacks to get the bullet to slide out to where the boat-tail/shank junction is holding it at the case mouth.

    Thoughts?
     

    MarkyMark007

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    Holding/seating tension is dependent from annealing like you see.

    I think this is because you shrink area where your brass has elastic deformation, but extend area where brass has plastic deformation. And when you reach area of plastic deformation, you will have smaller tension (or no tension at all) than in area where you have only elastic deformation.

    And I think that when you reach plastic deformation, you don't have bigger 'neck tension' with tighter bushing, because even you have 0.005' smaller bushing than loaded round, your bullet will expand neck and it may expand it to 0.001' when elastic deformation will hold your bullet. So it will be the same if you squeeze your neck 0.005' under or 0.002' under, and neck tension will be the same because you plastic deform neck when you seating your bullet. And when you will take your bullet out, the neck will be only 0.001' under bullet diameter. So only 0.001' of elastic deformation of the neck will hold your bullet - you will feel that seating force is way greater in '0.005' neck tension', but this neck tension will NOT hold your bullet, because you plastic deform your brass!


    metal-stress-strain-480x388.png



    stress_relax_plastically.png






    mXA2S3hpqidZjTyepsrGp9XL





    Next thing is your brass material, neck thickness, clean neck inside... All those things infect tension of the bullet. And if you still have too small tension - always crimp hunting bullets. I would reccomend for hunting round always crimp; for safety reasons.
     
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    MarkyMark007

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    KcP9ZBAm5B4QY1khxgMNYSFA


    As you can see, it does not take much neck tension to yield the case neck. With a .30 caliber bullet and hard brass, we hit it around 0.0015" of neck tension. .22 caliber bullets can only handle .001" of neck tension before yielding.

    So what does this actually mean? It means that unless you are using a very light neck tension and not annealing, you are plasticly deforming your brass when you seat a bullet.

    If you do not plastically deform your brass, the amount of force holding the bullet will be very consistent because the elastic modulus is very consistent and does not vary with brass hardness. If you do plastically deform your brass, and the yield point varies at all from case to case, you will introduce variation into your holding force because of the nonlinear relationship between stress and strain above the yield point.



    So you can see, that AMP press and other pressure gauges are not very usefull, because they do NOT show you the real value of the neck tension which is our goal: bullet release force! They show force for bullet to go into the neck...

    And with tighter bushings you dont get better bullet holding, but only plastic deformation of the neck and deformation of the bullet jacket, because your bullet acts like mandrell for neck expanding.
     
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    ArtOfStalk

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    @MarkyMark007
    That is some excellent information! Thank you for your explanation and the links. As an engineer this stuff is just what I was looking for - brain candy.

    So what I got out of it is that I need to wrap my case necks in rubber bands and heat shrink plastic on top. Got it. :unsure::rolleyes::ROFLMAO: