Mandrel sizing for consistent neck tension

Discussion in 'Reloading' started by sbruni, Oct 12, 2019 at 8:24 AM.


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  1. sbruni

    sbruni Well-Known Member

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    Have been working on a load for a new 6.5 PRC and settled on a pretty good load with RL26 that's pretty consistent .5 to .7 MOA... In the process I had some test rounds that were a little hot so pulled the bullets with an impact hammer and charged them with my final load and reseated the bullets... Now I usually use these as fouler thinking that the neck tension won't match the rest of my brass... This time I had enough that I thought what the heck I'll see if they group with the rest of the fl sized once fired brass... So the .098 MOA group that resulted has my attention.... I'm thinking there might be something to Mandrel sizing....

    So a few questions for those that have experience with mandrel sizing the ID
    1) who's mandrels do you use (stainless or TiN coated)?
    2) Do you inside lube before?
    3) Do you used the expander Mandrel? Or Turning?
    4) what relative size Bushing do you use?
    5) Any other keys to success?

    Thanks in advance for your help
     
  2. Mikecr

    Mikecr Well-Known Member

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    Sinclair, stainless, expansion, bushing 2thou under cal. Mandrel dry film coated with WS2. Soon, when available, I'll go to carbide mandrels at cal (not under). With this, necks would spring back to provide no more than true tension with minimal interference.
     
  3. hwy1strat

    hwy1strat Well-Known Member

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    I use K and M expand mandrels. I completely remove the neck expander ball/decapping pin from my dies. I resize and then neck expand. I use the Redding Lube. It is super simple to set up, but it stinks that you have to run all your brass through twice. My concentricity is far better with neck expanding this way
     
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  4. sbruni

    sbruni Well-Known Member

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    Not familiar with WS2... where can you get it?
     
  5. Deputy819

    Deputy819 Well-Known Member LRH Team Member

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    21st Century TiNi Turning Arbor 2thou under, bushing 3thou under, case necks dipped in Imperial Dry Lube before operation. Annealing before any case work/prep is done.
     
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  6. Mikecr

    Mikecr Well-Known Member

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  7. DocDoc

    DocDoc Well-Known Member

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    Mike,
    Why WS2 over HBN?
     
  8. Dirtdevil

    Dirtdevil Well-Known Member

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    Is that 2 thousand under actual bullet diameter Ex .283 bullet so .281 dia mandrel. I see a lot of guys talking and Sinclair mandrels but the only ones I have found are 1thous under size. .282 diameter
     
  9. Mikecr

    Mikecr Well-Known Member

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    I don't know a lot about HBN, never used it. I've been using WS2 since the early 80s.
    What I know about WS2 is that it seems to universally match powder fouling. So I use it to coat bullets and dry pre-foul bores, putting guns away fully ready for use.
    When I pull a gun for hunting or range session, the 1st shot is as good as any to follow.
    It reduces copper fouling, as it fills voids and copper won't stick to it.
    It's cheap and easy to use. I can see the coating polish up with a mirror finish, and see any spots missed. A cup of it could last several lifetimes of reloading.
    And best of all, it cleans right out with no special agents or actions.
     
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  10. nksmfamjp

    nksmfamjp Well-Known Member

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    1) K&M standard
    2) yes, Hornady bucket lube
    3) same expander as I use to set up for turning
    4) I use std Forster dies without removing the mandral.
    5) My process is still under development...since I just blew out 2 necks after about 4-6 loadings, I plan to do something to reduce working brass or add in annealing.
     
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  11. Mikecr

    Mikecr Well-Known Member

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    Sinclair now offers carbide expander mandrels, 1thou under cal:
    https://www.sinclairintl.com/reload...els/carbide-expander-mandrels-prod119668.aspx
    So for 7mm, which should be .284" bullets, their expander mandrel measures .283".
    Necks will spring back (inward) ~1/2thou from this, leaving .2825", or 1.5thou seating interference.

    Bushing selection (trial & error) to downsize necks to .281 works well. Necks would spring back(outward) ~1/2thou to .2815" interference. The .283" mandrel then sizes up 1thou(after spring back), to .2825" as mentioned.
    Personally, I would prefer interference set at .283. That's what I'm waiting for before replacing what I have ($$$)
    Bushing selection is trial & error because of the sizing angles presented by necks expanded into whatever chamber neck clearance you have. With this, I've been lucky starting at 2thou under cal, and using expander mandrels.
     
  12. highdrum

    highdrum Well-Known Member

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    I use a bushing typically 2-3 thou under loaded diameter, i have carbine and ti-N expanding mandrels(1 thou under bullet od) and neck turning mandrels(2 thou under bullet od) I don't neck turn yet......but plan to start doing so to clean up the neck inconsistencies, as I believe that's where some my runout at neck is coming from. I do not lube necks prior to running the mandrel into the neck, as carbide and ti-N don't really need it. I DO however set up my mandrel die as high as possible with just enough depth to fully size the neck with ram of press at full stroke. I dip the bullet into graphite dry neck lube prior to seating. Most all my rounds are loaded with 2-3 thou neck tension. I haven't noticed a lot of difference in groups. I do believe my reloading practices are a lot better than my shooting though. I get low teens to single digit SD, and upper teens ES but only manage 1/2 to 3/4 moa groups. I need more trigger time.......
     
  13. sbruni

    sbruni Well-Known Member

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    Thanks.... appreciate all you input. It would have been pretty foolish to not google it first. What I found was many websites with whole catalogs of WS2 products to offer. Assumed you were referring to a firearms specific product so assumed I was on the wrong path. Based on your response I guess I can assume that it’s all the same stuff... and also get the impression it’s pretty similar to moly
     
  14. AZShooter

    AZShooter Well-Known Member

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    Interesting information. There is an extra factor that has me wondering if it might be what is making the difference. Inside neck lube is used with the mandrel. Anyone try using a bushing to get finalized neck tension with neck lube as a control?

    I know bullet lubes like moly and HBN help with bullet release perhaps the lube is doing the same thing?