Pulling bullets / Reseating / Neck Tension

Discussion in 'Reloading' started by woods, May 27, 2013.

  1. woods

    woods Well-Known Member

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    I recently did a test on pulling bullets and the resultant ID of necks to post on another forum about the NECESSITY for resizing after bullet pulls. Took pictures to document. These were all loads taken at random from my load boxes for 5 different calibers:

    30-06 - marked 06-1
    375 Ruger - marked 75-1 for the existing load and 3 NEW cases marked 75-2, 75-3 & 374-4 added later not shown in original pic
    6.5 rem mag - marked 6.5-1
    338RUM - marked 338-1
    280AI - marked 280-1

    [​IMG]

    I pulled the bullets with a press mounted die type collet puller and measured the ID's with pin gauges. In each case I would try the caliber size pin and go down until one fit

    The 30-06 case had a snug fit on a .306" pin
    [​IMG]

    The 375 Ruger case had a snug fit on a .373" pin
    [​IMG]

    The 6.5 rem mag case had a snug fit on a .262" pin
    [​IMG]

    The 338RUM had a loose fit on a .336" pin
    [​IMG]

    The 280AI had a tight fit on a .282" pin
    [​IMG]


    This will be a double post since you can only put 6 links in any one post and on the 375 Ruger I wanted to seat bullets into cases with different original ID's and see what they came back to.

    However, my question would be

    Why would any resizing be necessary if you always have a perfectly round neck expanded by the bullet and the bullet grip / inside diameter is always ~.002" below caliber? Most of these threads 90% of the posters all say you have to resize. Is that just the throw down or default answer or am I missing something here?
     
  2. woods

    woods Well-Known Member

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    The 375 Ruger is the only caliber I can come up with where I can start with greatly varying ID's since that is the only one I size with a FL sizer. All others are sized with a Lee Collet or Redding Bushing (only 2 bushing sizes on hand)

    375 Ruger - NEW CASE UNSIZED before seating bullet .372" after pulling bullet .373"
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    [​IMG]

    375 Ruger - NEW CASE SIZED WITH EXPANDER before seating bullet .371" after pulling bullet .373"
    [​IMG]
    [​IMG]

    375 Ruger - NEW CASE SIZED WITHOUT EXPANDER before seating bullet .361" (I really need to get around to ordering a Lee Collet and a .372" mandrel for it bad) after pulling bullet .373"
    [​IMG]
    [​IMG]

    So it seems that all ID's return to the same place

    Food for thought
     

  3. 375fan

    375fan Well-Known Member

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    Woods,
    Great report. question: do you know how many times cases used for report were loaded/fired/annealed?
    Where do you get pin gauges like you used?
    Thanks, Jeff
     
  4. woods

    woods Well-Known Member

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    06 once fired
    375 Ruger 3 times fired
    6.5 rem mag 4 times fired
    338RUM once fired
    280AI twice fired

    [​IMG]

    Lost my link to the pin gauges, will do a search for old posts and see if I can find it but it will be later tonight
     
  5. barnesuser28

    barnesuser28 Well-Known Member

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    I did a quick search on your posts, is this it? CDCO Machinery Corp.
     
  6. Mikecr

    Mikecr Well-Known Member

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    You would not need to resize necks, as normal springback(your 2thou) provides plenty of grip. That springback is all that grips a bullet even if necks are downsized way more. A bullet will just re-upsize to cal, with springback gripping it, over & over.
    With fitted chamber necks, no neck sizing is needed at all to reload, as the necks spring right back from chamber neck to under-cal(ready to recieve another bullet).

    Would it surprise you if 90% of posters were wrong?
    How many do you think have tested this like you just did?
     
  7. woods

    woods Well-Known Member

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    I guess it does surprise me if the percentage is correct at 90%. Just pulled that percentage out of the air so it might be less. Wouldn't surprise me if it was 60% that were wrong. Seems like there are a lot of rote reloaders who hear several say something and bingo, must be true. Sometimes it might be easier if I didn't have to prove everything to myself.

    You mentioned springback and that is a seemingly simple concept that is just mentioned in passing and never fully explained. Went looking for proof or facts several years ago about the simple question of whether soft brass or work hardened brass had more springback. Never found any, just one article in a gun rag that SAID that work hardened brass had more springback.

    It seems intuitive to me that soft brass would have more springback since brass expansion in a chamber as regards shoulder movement gets progressively less as the brass is work hardened. i.e. the shoulder moves forward approx. 85% of the total distance it will expand on the first firing, approx. 10% on the second firing and doesn't springback at all on the 3rd or 4th firing when it develops a crush fit.

    IOW very little is known (at least by me) about the variables that influence the amount of springback. i.e. when, where & why

    So do you have any explanation why the cases of mine that had been fired more often did not return to a different dimension? Or is the variation in springback in work hardened brass as opposed to new soft brass negligible or so small that it doesn't exhibit itself in thousandths?
     
  8. 375fan

    375fan Well-Known Member

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    Since the chamber (specificlly around neck) restricts how far the brass can go in a outward manner when cartridge is fired coupled with the heating of brass from hot gases of powder burning then when brass cools, the cooling produces slight annealing/shrinkage of brass?
    Just a thought/theory I have.
     
  9. woods

    woods Well-Known Member

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    Certainly the neck brass will springback some after firing. Not sure if the heat from the firing will have any annealing effect.

    3 of the loads in the original post are custom tight necked chambers, the 6.5 rem mag, 338RUM & the 280AI. The 280AI is stamped ".313" neck" but the fired case OD is ~.311", so there is ~.002" springback on the neck after firing also.

    The 375 Ruger was chambered with a standard reamer, at least that is what I told the smith, and the fired OD is .005" larger than the loaded round OD. Figuring a little springback, I would assume I have .007" neck clearance.

    The 06 is a factory Steyr and it has a .0085" difference in OD between fired neck and loaded round, so it must be close to .010"+ neck clearance.
     
  10. Mikecr

    Mikecr Well-Known Member

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    Hardened brass springs back more.
    You're not hardening brass with fired expansion, you're taking it to yield.
    When brass is expanded let's say 3thou(1thou beyond springback), it yields 1thou and springs backs slightly less than expected 2thou -because it is now thinner. This action happens with each firing provided you're running high enough pressures, or with low shoulder angles/high body taper/big clearances, to cause yielding(although less & less of it). Unmanaged, it leads to extraction problems.

    The answer to extraction problems is NOT loose chambers, or big sizing. It's managing load pressure for the amount of barrel steel around a given chamber area to control brass yielding. This, followed by sizing that maintains target springback, produces stable brass that works well, lasts forever, and without FL sizing(just shoulder bumps & partial neck sizing).

    With a case designed with high shoulder angles, low body taper, fired in low chamber clearances at moderate pressures, it's possible to eliminate sizing in reloading all together. The brass will not yield and just spring right back to set dimensions.
    I nearly managed this with my 6.5WSSM, but 35deg shoulder angles are still too shallow. Next chamber will provide 45deg shoulders. Necks are fitted, and I don't have to size them.
     
  11. eshorebwhntr

    eshorebwhntr Well-Known Member

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    Finally a post in the reloading section with some intelligent discussion and factual data to back it up. Great info.

    Just wanted to add as a side note a finding that I had a few weeks ago in regard to neck sizing.

    I've got a custom chamber STW by Gre-Tan. It was cut with a .313 neck based on the dummy cartridge I sent with Remington brass. Now that there is short supply of that brass and since I had heard many good things about Norma I fire-formed some for my rifle from 300 H&H brass a while back. Once loaded up the neck diameter with the norma brass is only .310, so .003 clearance as opposed to a tight fit with the Remington.

    So far I've only been able to shoot at 100 yards for comparison but there is a fall off in accuracy with the Norma brass. It's not much, but it is noticeable. This gun would consistently cut one hole at that range and now its more like a clover leaf. I still need to continue with load development but so far that is what I've found. I also noticed a higher spread in velocity as well. Both probably deserve more testing at this stage but I thought it was worth sharing.

    Another note...if you start out wondering what size bushing to use don't try to mic the wall thickness and double it to calculate the bushing diameter. Find a way to size it down enough to get a tight fit on the bullet and mic the neck of a loaded round. Much more accurate and gets you the correct bushing the first time. I learned the hard way, hopefully someone else reads this down the road and it saves them some hassle.
     
  12. woods

    woods Well-Known Member

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    Well I'm not into benchrest but do like to control things. So I outside neck turn for .003" neck clearance. That allows me to trap the neck between a Forster outside turner and an inside reamer for a very consistant neck thickness

    [​IMG]
    [​IMG]

    The reamer is .003" over caliber so after fire forming it will fit if I have .003" neck clearance on the load. With springback thrown in, now I know why the reamer has always been so tight.

    Mike, one thing I'm confused about

    Does that depend upon how much it is expanded? For instance in my factory 06 the neck clearance is .010". So wouldn't that much expansion work harden brass also like sizing the neck down with a die?
     
  13. X-man

    X-man Well-Known Member

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    I don't think case neck spring back has much to do with case hardness.

    The reason I think this is back in the day some benchresters used to turn their brass (tight neck chamber) so they didn't have to re-size the neck until they needed to move the shoulder back. I know for a fact the case neck is a lot harder after 5 plus firings yet the neck spring back was the same.

    What tends to complicate the issue is the neck thicken over several firings and this will start creating different spring back until the necks are turned back to spec. If I remember right the spec was 1-1.5 thou over all...very tight! Rifles set up this way shot well enough, but the slightest bit of carbon or whatever in the neck area caused significant fliers and pressure spikes.

    I never re size brass after pulling a bullet.
     
  14. Mikecr

    Mikecr Well-Known Member

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    Neither upsizing, nor downsizing hardens brass. It's only when BOTH actions are taken that work hardening occurs.

    With this, your neck expands 10thou meeting the chamber neck and continues following chamber neck expansion, until springing back on pressure release as it would given it's new thickness and normal hardness. If the necks were truly annealed(all energy removed), they would not spring back and could be left with an interference fit with chamber neck.
    Now once you size down the normal neck to ~1-2thou under cal, you have completed one hardening cycle, and the case neck should spring back outward from whatever sizing needed to leave you with ~1-2thou under. It's typical to need 3-4thou under cal worth of sizing to be left with 1-2thou under cal after springback.
    If you sized down more than 3-4thou under cal, you should expand necks to cal, leaving 1-2thou under after springback(inward). No good in going overbored, and bushings can only produce predictable result with 5thou or less of sizing.