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Thread: RCBS neck sizing question

  1. #1

    RCBS neck sizing question

    Hi guys,

    I neck size my cases with basic RCBS dies. On the depriming pin is the expander which obviously expands the neck to the required size, giving a certain neck tension. Does anyone know if you can buy different sized expanders for these dies as theyre screw on/off as if i can, i can alter neck tension. With the standard die, ive got 6 thou of neck tension, i would like to try and reduce it to 3-4 thou..



  2. #2
    Generally, not. What you can do it to pick up an expander ball for a .303 or 7.62x39 or similar cartridge, chuck the expander rod, with the ball mounted, in a drill press or electric hand drill and stone it down to the required size. One of reasons I like the Lee Collet Die is variable neck tension (up to a point) without the bother.~Muir

  3. #3
    What caliber is it - assuming 7mm-08? at 6 thou tension is a lot of tension.
    Even if you did change the expander you are working the brass a lot more than is needed i.e. shrinking down then opening up again which won't do wonders for brass life.

    Bushwear sell decapping pins and expander balls for RCBS but for different calibers, not custom sizes.

    You could go the bushing die route, bushes come in increments of 1 thou.

  4. #4
    Yikes. How was I thinking this was a 308 we were talking about?? What caliber is it? My answer would be the same, though.~Muir

  5. #5
    Thanks guys,

    It is 7-08 Muir, you were probably thinking of that remmy 700 in .308 i used to have. Ok, so i may be able to mess around and make an expander which would reduce the neck tension however i agree that it is working the brass more than is necessary. So what dies would you recommend which i can get bushes for?

  6. #6
    Redding Comps are about the only game in town that a working man can afford. You could take a standard 30 cal expander ball and treat is as I described. Start with coarse stones and work it down to where you want it. Better yet, find a guy with a lathe and buy him a beer or two...~Muir

  7. #7
    Thats what i was thinking Muir, get a guy with a lathe to knock a couple of different ones doesnt get round working the cases more than necessary.. I have read that you need at least 2 thou of neck tension to hold the bullet in place but would as little as 3 thou have enough grip to hold a round in a mag when the rifle is being fired? Any experience with this?

  8. #8
    I am a huge fan of neck tension unless it's carried to the extreme. (Usually you find out about too little tension at the wrong time.) A lot depends on the brass and it's elasticity. You may find that this expander ball is just fine with another LOT of brass. I also tend to crimp my brass so that worries about dislodging a bullet during recoil is minimized.

    I once sized my .222 to .001" tension (finger tight seating) but put a shoulder below the bullet base with a 22 Hornet Lee Crimp Die that kept the bullet from traveling deeper into the case for whatever reason. The loads shot well. I'm guessing, based on that experience, that .002 would be tough to keep seated during recoil of a 7-08 and .003 would be minimal. Of course, that depends on seating depth and the amount of surface area applied to the bullet by the neck.

    Why don't you make up some balls, and see how the different tension effects the accuracy and stability of the rounds and let us know? It would make a great write-up.~Muir

  9. #9
    Cheers Muir, will have to find someone willing to manufacture.. may see if we have a metalwork guy at work.. It would be very interesting. Theres plenty of bullet in the neck, certainly more than .284. Even with the rounds on the lands, it would be over .284 however then i get to the same old problem of the rounds not fitting in the mag. Ive been tinkering with the VLDs which are giving great results on the lands and closer, but the longest i can get them to fit in the mag puts them 36 thou off the lands, so im going to continue to play to see what is optimum..

    This reloading thing is like picking a scab.. just cant stop once you have started!!

  10. #10
    Quote Originally Posted by flyingfisherman View Post
    This reloading thing is like picking a scab.. just cant stop once you have started!!
    Tell me about it! I once got positively obsessed with the idea of shooting 38 Super cartridges from a modified Spanish Destroyer Carbine. I altered the bolt face and proceeded to spend a year or better firing shotgun-pattern groups at 25M before I finally buried it in the back yard. Nothing worked. Still gives me nightmares...~Muir

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