Bumping shoulder max
Join Today
Results 1 to 4 of 4
  1. #1
    Member
    Join Date
    Mar 2016
    Posts
    39

    Bumping shoulder max

    Ruined an RCBS FL die the other day with a stuck case, so I went and bought a Lee set. Having recently picked up an RCBS precision mic I thought I would pull out some of my oldest and most expendable brass to learn/observe a good technique for bumping the shoulders back a couple thou. The first thing I see is that not all brass being equal some shoulders set back .004 and others .002/.001. This being based from a fired case, which on my mic is at the .000 line.
    I am setting aside the longer headspace to stop and ask the rest of you what is considered safe or pushing it just right. With my LC brass it is a real fight and others a breeze.
    I appreciate your guidance!

    Thx

  2. #2
    Senior Member Deadshot2's Avatar
    Join Date
    Aug 2012
    Location
    Behind Enemy Lines
    Posts
    2,334
    When bending or "moving" metal you have to take into consideration the spring-back. When moving shoulders back or for that matter sizing necks, you have to exceed the "modulus of elasticity". The point you displace metal and it doesn't return to it's original position when pressure is released.

    This "Modulus" in brass depends greatly on the hardness of the brass. If you want uniform shoulder "bump" or neck sizing you just about have to anneal. For me i consider it a necessity. LC brass is a little tougher than let's say winchester or Remington (R-P headstamp). If you don't anneal yet, get a heavy deep impact socket that the brass just slips into. It should stop with just the shoulder area sticking out with just a portion of case sidewall exposed. With a 1/4 drive adapter that fits in a cordless drill and fits the socket, chuck it up in a drill. Using a butane torch, spin the brass in the flame until it shows a fairly pronounced blue color without glowing red. It takes me about 4 seconds in the flame to anneal a case.

    Drop the hot case in a metal bowl and you don't need to quench it in water. Doesn't help the annealing and just makes wet cases.

    Then try bumping shoulders and you should see some consistent readings with your mic. Last item of importance, make sure your press is pushing he die the same amount. If in doubt use shim washers to adjust setback rather than backing out or screwing in die. Can also use a Redding Competition Die Set which has shell holders that are are ground with .002" increments so you can lower the case in same amounts. Start with the "+ .010" shell holder and size case. Check shoulder setback. If not where you want it, move to +.008" and repeat. As an example I find that using the .006" shell holder gives me a perfect shoulder setback on my annealed cases with the die screwed in to the point where the press "cams over". By adjusting the die to his point there is no slack in the press and I'm putting the same pressure every time on the case.

  3. #3
    Member
    Join Date
    Mar 2016
    Posts
    39
    Thanks for that reply! Ha, that's twice now you've made me pull the dictionary out. First was "spall" when describing the deflection of the rounds I was firing into a steel back stop. I was explaining my need for a different bullet catch to a friend of mine and used that word, with a bit of confidence. He asked "what the heck is spall?" Of course I had to question him on his apparent lack of common education. Now "modulus".
    Awesome!

    I will rummage through my tool box for a socket.

    I will need to look into a fix for keeping a regularity to my press as I believe that when the cam over is completed some brass that read +.001 ends up being -.001 to -.004 with an occasional -.005. Now being the sponge for knowledge that I am I read the columns online about this spring back. Question: how to I determine if I've reached this modulus without blowing out a case or worse? I am leery against using the brass I squished, though measuring some factory rounds (Federal) I get between -3 to -4 thou.
    Last edited by Shazz; 03-11-2017 at 10:44 AM.

  4. Remove Advertisements
    700Rifle.com
    Advertisements
     

  5. #4
    Senior Member Deadshot2's Avatar
    Join Date
    Aug 2012
    Location
    Behind Enemy Lines
    Posts
    2,334
    Quote Originally Posted by Shazz View Post
    Thanks for that reply! Ha, that's twice now you've made me pull the dictionary out. First was "spall" when describing the deflection of the rounds I was firing into a steel back stop. I was explaining my need for a different bullet catch to a friend of mine and used that word, with a bit of confidence. He asked "what the heck is spall?" Of course I had to question him on his apparent lack of common education. Now "modulus".
    Awesome!

    I will rummage through my tool box for a socket.

    I will need to look into a fix for keeping a regularity to my press as I believe that when the cam over is completed some brass that read +.001 ends up being -.001 to -.004 with an occasional -.005. Now being the sponge for knowledge that I am I read the columns online about this spring back. Question: how to I determine if I've reached this modulus without blowing out a case or worse? I am leery against using the brass I squished, though measuring some factory rounds (Federal) I get between -3 to -4 thou.

    Brass with a little extra shoulder bump is not dangerous to use. Not if only a few thousandths. It can be an issue if you have a stacked series of problems. If your primers are seated too deep (due to a deeper primer pocket, your rifle has a little extra headspace, and you bumped the shoulder back a little extra, those "tolerances" can stack and you may have a round that won't fire because of insufficient strike from the firing pin.

    Brass with just a little extra "bump" works more and could lead to premature failure due to work hardening. That extra bump will disappear as soon as you fire the round.

    As for "cam over", that only works for regulating shoulder bump if you are using the Redding Shell holders with the .002" steps or if you are using shims between the bottom of the die and your standard shell holder. Get a shim stock assortment and cut some case sized holes in various thickness pieces. Place over case about to be sized and adjust die so it locks tight against shell holder. Start with a thick enough shim it doesn't push the shoulder back then replace with thinner shims until you get to the right shoulder bump and a die that's tight against the shell holder (press cammed over).

    As for knowing when you've reached the "modulus" for any given piece of brass, you either have to adjust and measure for each as I described above or anneal so the cases are more consistent in their elasticity.


 

Similar Threads

  1. 168gr A-Max BC 0.40????
    By Str8shot in forum Handloading Techniques
    Replies: 3
    Last Post: 02-29-2016, 09:58 AM
  2. 208gr A-Max
    By M700 in forum Handloading Techniques
    Replies: 0
    Last Post: 02-27-2014, 06:56 AM
  3. 208gr A-Max
    By M700 in forum Handloading Techniques
    Replies: 12
    Last Post: 03-11-2013, 10:46 AM
  4. 53 gr V-MAX in 223
    By COhntr in forum Handloading Techniques
    Replies: 3
    Last Post: 02-19-2013, 07:18 PM
  5. A-Max are the bomb!
    By derrelw in forum Handloading Techniques
    Replies: 2
    Last Post: 01-18-2013, 08:30 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •