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Thread: full length neck expander button

  1. #1
    Boolit Master Idz's Avatar
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    Question full length neck expander button

    I was having difficulty with my PC soft lead cast bullets getting shaved while seating. I prefer soft bullets because they are easy on steel plate targets. I tried de-burring the case mouth and using the Lyman M die with some success but still was getting shaving and some barrel leading. As a test I made a sizing buttons for 45acp at 0.455 diameter and 9mm at 0.360 diameter that were long enough so the bullet could be set in the case with only another 0.050" push required by the seating die.
    Shaving disappeared and accuracy increased! Even with only minimal neck tension I had no difficulty with bullet jump and the barrel looked much cleaner indicating good powder burn.
    With case springback my long expanders gave 0.452-0.453 for my 45acp bullets sized at 0.452 and the 9mm cases sprung back to 0.357-0.358 for a 0.357 sized bullet.

    I know neck tension is important for rifle bullets to get the slow powders burning properly but is it that important for fast pistol powders?

    Anybody else experiment with this?

  2. #2
    Boolit Master
    mdi's Avatar
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    You are sizing the case ID/mouths to .455" and .360" (with a "button")? Or am I reading your post wrong? My 45 ACP bullets run .452" and my 9mm about .357" so sizing the ID to the dimensions in your post would be disastrous for me...
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  3. #3
    Boolit Master Idz's Avatar
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    The sizing buttons (cylinders) are .455 and .360 , unless you anneal your brass dead soft the cases spring back to a smaller ID which is usually about .002-.003 smaller than the button. This gives me a nice slip fit of the bullet into the case. Then the taper crimp seating die pushes the bullet the final .050" and gives the mouth a slight taper crimp.

  4. #4
    Boolit Master


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    Most think that .002 is the proper interference fit between boolit and case mouth. You seem to be a little oversize but if it is working go with it.

  5. #5
    Boolit Master gpidaho's Avatar
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    All part of why I'm such a fan of Noe tooling. With their expander plugs you can get the exact amount of neck tension you want. Gp

  6. #6
    Boolit Master Idz's Avatar
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    I guess I'll keep playing around with this. As far as I can tell, a lot of the mythology about neck tension was developed back in the blackpowder rifle and revolver days. It seems that the engraving forces far exceed the neck tension forces so semi-autos need almost zero neck tension to function.

  7. #7
    Boolit Master
    mdi's Avatar
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    I guess I don't understand. If one used a tool to expand the case ID to .455", what keeps a .452" bullet in place? Even if the case ID is .453", .001"interference fit ain't very much and bullets will be loose...

    In a semi-auto the cartridge is ripped out of the magazine, slammed up the feed ramp and into the chamber and loose bullet/case fit can move the bullet in the case, BTDT!

    I guess it's cool if it works for you...
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  8. #8
    Boolit Master
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    If Im reading this correctly, the OP is saying after the large expander button is removed from the case, the brass is springing back to almost exactly what the diameter of the boolit is. This allows the boolit to be seated without shaving. It is probably creating that coke bottle shape most of us get,thus not allowing boolit setback. Plus he is putting a slight taper crimp on the boolit to ensure no boolit setback. I don't see the problem in this especially if he is using soft boolits. As long as there is no setback, run with it dude.

  9. #9
    Boolit Master
    mdi's Avatar
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    OK, but this is why I flare the case mouths to load cast bullets. My fit is around .003" depending on gun to bullet fit. I also have a couple M dies, but they still leave a square edge and shaving is possible (simple, you can't push a .452" slug into a .449" tube without a tapered "entry way" or flare)...
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  10. #10
    Boolit Master

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    a lot of my hollow based wadcutters are soft seated in the cases for my wad cutter gun. It des improve accuracy. one is the case is a better fit to the chamber and better supported and second the bullets soft hollow base ring isn't as deformed.
    My expander is full length with a full dia end for .300 from end and a radius to smooth entry. its then relieved .010 to the belling angle on the stem, this lowers the drag from a full length full dia rod. For loght target loads this works well.
    My Match rifle in 243 showed definite preferences in neck tension. here I used bushing dies instead of an expander button. But groups could be fine tuned the last little bit thru adjusting neck tension. Another tool in finding the utmost accuracy

  11. #11
    Boolit Master Char-Gar's Avatar
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    For handgun rounds, I have long used the expanders made by Lyman for their 310 tool and the Tru-Line Jr. presses. These are very similiar to the M dies, having a full length expanding body with a 2nd. step at the top to allow seating the bullet without shaving.

    For the 45 ACP, the expander is .452 and the top step is .460. This allows the bullet to go down without shaving. With the case spring back and a taper crimp the loaded rounds are near to perfect in my opinion.
    Disclaimer: The above is not holy writ. It is just my opinion based on my experience and knowledge. Your mileage may vary.

  12. #12
    Boolit Master
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    You don't need to size your cases that oversize AND that DEEPLY, leaving only 0.050" of (still undersized) neck tension.

    IMO, what you want is a neck expander that is exactly the same diameter of your bullets. So for a 452 bullet, you want a 452 expander. But with a step of 455 that only flares the mouth about 10-20 mils deep. That's all you need to prevent bullet shaving and to aid in straight, concentric seating. This is more or less how NOE and M dies are shaped, but they don't come big enough. NOE is great, but even they will only have the right size expanders in 9mm and 45ACP, off the shelf. And that's because 357 and 45 Colt exist.

    If you want custom sizes, you can get them machined by NOE by custom order. Or you can find your own machinist. Or you can buy oversized (wrong caliber) M dies and turn them yourself with a low runout drill and a rotary tool and a $10.00 caliper. It's pretty easy.

    The problem with 50 thousandths* length of neck tension is not with the powder. If you only shoot revolvers, it is fine. In a semiauto, compromised neck tension can lead to setback during feeding.** If your sizing plug is the same diameter as your bullet, you will have proper neck tension. 3 mils over, like you are using, and you are greatly compromising neck tension and relying only on the base of the bullet to prevent setback. Neck tension comes primarily from the case mouth/neck around the bullet. Even if the case is undersized behind the bullet, that does jack compared to proper neck tension.

    Expanding the case ALL the way down to where the base of the bullet sits will often improve your accuracy and reduce fouling, as well, when using very soft bullets. Just make sure the plug isn't larger than the bullet. If you're paranoid, you can go 1 mil under. But 9mm cases, in particular, will swage the heck out of a soft cast bullet, when you leave them underexpanded. If the swaged bullet is still bigger than your bore, you will probably be ok. But it doesn't hurt to completely eliminate case-swaging by completely expanding the necks (that is, as long as the cartridge will still chamber; it's possible that your chamber is too tight to do this for your bullet).

    *I suppose in 9mm (where the amount of bullet that gets seated is pretty short), using a very short bullet, 50 thousandths might be pretty close to all you get, anyway. But IME, 9mm cast bullet profiles seat pretty deep.

    ** I once had an unsized case slip into my pile. Had a failure to fire. Opened up the chamber of my semiauto pistol. And I extract a cartridge full of powder and with the nose of the bullet flush with the case mouth. Luckily, I size and prime my cases in the same step, so this case had a spent primer.
    Last edited by gloob; 07-10-2018 at 09:57 PM.

  13. #13
    Boolit Master


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    I am glad this thread came up and your talking about neck tension. This is the most under rated or ignored step in reloading cast bullets, this is the #1 problem when reloading 9mm, 40, 10 and sometimes 45 acp. I just wish expander buttons were easier to find. ( Or am i just not looking in the right places)
    A rule of thumb for me is Cast bullets need or only need .002 -.003 neck tension. Jacketed seem to be around .005 to .006 neck tension, with adjustments for accuracy. When measuring keep spring back of brass in mind.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check