Results 1 to 6 of 6

Thread: I got a bargain...or maybe I didn't!

  1. #1

    I got a bargain...or maybe I didn't!

    Chasing around looking for the exact headspace in my rifle, I happened upon an RCBS Precision Mic. tool (Correct calibre) used, for a tenner (usually around £65). I simply cannot understand how it measures! Yes I can see the marks, but no dimension seems to tally even closely with my other guage.

    I had also done the usual thing & bought a Hornady Headspace Guage with the correct bushing & taking a fired case did the measurements on a number of cases, then selected a mean average. In my case, 2.049".
    So, I set me F/L sizing die using an 'O' ring enabling me to get finite adjustment to size to 2.048".
    No problem.

    Then, just to see where I can get to in terms of + tolerance, I start measuring using rizla papers at the cartridge head (base) and measuring from the shoulder datum point including the paper (Not successful so I started using kitchen foil cut to size) and I get to 2.0515" headspace measurement.
    this gives me a go/no-go dimension.

    So a question: What actually is my actual headspace?
    Is it a) the fired case average dimesion 2.049"?
    or b) the final 'go' dimension lets say 2.051"


    Adjusting my sizing die to size brass at 2.051" will ensure the finished cartridge chambers and fires in my rifle. Is it likely as a result to be more accurate by a degree or two?
    or is it just easier on the brass?


    Is there anyone out there able to enlighten me further please?
    Cheers. d
    Blaser K95 Luxus Kipplaufbüchse .25-06Rem. Zeiss 8x56, 110gn Nosler Accubond = Game Over!

  2. #2
    Quote Originally Posted by deeangeo View Post
    Chasing around looking for the exact headspace in my rifle, I happened upon an RCBS Precision Mic. tool (Correct calibre) used, for a tenner (usually around £65). I simply cannot understand how it measures! Yes I can see the marks, but no dimension seems to tally even closely with my other guage.

    I had also done the usual thing & bought a Hornady Headspace Guage with the correct bushing & taking a fired case did the measurements on a number of cases, then selected a mean average. In my case, 2.049".
    So, I set me F/L sizing die using an 'O' ring enabling me to get finite adjustment to size to 2.048".
    No problem.

    Then, just to see where I can get to in terms of + tolerance, I start measuring using rizla papers at the cartridge head (base) and measuring from the shoulder datum point including the paper (Not successful so I started using kitchen foil cut to size) and I get to 2.0515" headspace measurement.
    this gives me a go/no-go dimension.

    So a question: What actually is my actual headspace?
    Is it a) the fired case average dimesion 2.049"?
    or b) the final 'go' dimension lets say 2.051"


    Adjusting my sizing die to size brass at 2.051" will ensure the finished cartridge chambers and fires in my rifle. Is it likely as a result to be more accurate by a degree or two?
    or is it just easier on the brass?


    Is there anyone out there able to enlighten me further please?
    Cheers. d

    Sure.
    Quit worrying about it.~Muir

    But that said, What are you trying to accomplish?

  3. #3
    I have used the RCBS precision micrometre in various calibres for several years. I mainly use mine for establishing bullet seating depth measurements as to date I have always full-length resized.
    The measurements on the headspace (shoulder) if compared against an unfired case, will tell you by how much the shoulder moves when fired in your rifle. You can then adjust your die to move it back only as far as necessary. I believe that the markings on the tool relate only to themselves to enable comparison with each mark representing one thousandth of an inch.
    I will risk getting shot down in flames by others who are more technically competent, however I believe that the measurements on the bullet seating part relate only to themselves and are not relevant to anything else. To explain further, I seat my 85 grain .243 bullets at a measurement of +125 on the RCBS micrometre which is 10 thou short of the origin of the rifling. Touching the rifling would measure +135 on the micrometre. The measurement is to the ogive of the bullet. I think it is a good tool for establishing overall length.

  4. #4
    Headspace is actually a dimension taken from the rifle chamber not a fired/unfired case
    It is the distance from the bolt face to a datum point on the shoulder of specified diametre.
    In the case of a 30-06 its the distance from the bolt face to a point on the shoulder where the diametre is .375"
    Check out the SAAMI chamber and cartridge specs page: http://www.saami.org/PubResources/CC...0-%20Rifle.pdf

    Ian.

  5. #5
    Quote Originally Posted by Whitebeard View Post
    Headspace is actually a dimension taken from the rifle chamber not a fired/unfired case
    It is the distance from the bolt face to a datum point on the shoulder of specified diametre.
    In the case of a 30-06 its the distance from the bolt face to a point on the shoulder where the diametre is .375"
    Check out the SAAMI chamber and cartridge specs page: http://www.saami.org/PubResources/CC...0-%20Rifle.pdf

    Ian.
    Thanks for that, 'headspace' was clearly the wrong term. I suppose I was thinking that the bottlenecked cartridge headspaces on the case shoulder ?
    The RCBS micrometre will do two things for the OP. It will tell him how much the shoulder moves and what the maximum overall length can be with the bullet touching the rifling. It will enable him to know how far from the rifling his bullets are seated in comparison with the maximum and to seat them consistently.
    I think all the markings relate only to themselves. Having said that the indications that they give must have a measurable value ?
    That's about the best I can do to help, despite having used the tool for years. I sympathise with the OP in using it for the first time, as I remember struggling to get my head around it.

  6. #6
    OK guys I got it ...the term 'headspace' is incorrect in context of a fired case. As mentioned & which I already knew, it is the internal measurement from a datum point approx. midway on the shoulder to the bolt face. Therefore the correct headspace measurement will be the final 'go' measurement before a 'no-go' dimension is reached.
    Therefore the fired case dimension is a useable but not necessarily a finite dimension.

    Following a conversation with my good friend nutty spaniel, I now realise the tool is just a guage and & unlike the Hornady h/space guage for measuring the shoulder datum to case head using a vernier, doesn't give an inclusive total dimension, but simply shows - perhaps more acurately the correct dimension to be reached when setting up the F/L sizing die. I understand.

    @ Muir, simply trying to work out how the tool is used & what parameters it measures...to aid consistency in achieving prepped brass that's not 'overworked' & hopefully give a little more aid to accuracy.
    ATB all & thanks.
    Blaser K95 Luxus Kipplaufbüchse .25-06Rem. Zeiss 8x56, 110gn Nosler Accubond = Game Over!

Similar Threads

  1. Didn't know whether to post this here on in funnies
    By willie_gunn in forum Deer Dogs & Tracking
    Replies: 2
    Last Post: 12-10-2013, 11:08
  2. I didn't take my own advice
    By Scots_stalker in forum Deer Stalking General
    Replies: 75
    Last Post: 22-08-2013, 14:32
  3. some Stuff you didn't know you didn't know ....
    By steve109 in forum Jokes & Funnies
    Replies: 0
    Last Post: 30-01-2012, 17:32
  4. Hope they didn't.
    By Frax in forum Deer Stalking General
    Replies: 10
    Last Post: 05-06-2010, 19:21
  5. Didn't know it was here!
    By finnbear270 in forum Deer Stalking General
    Replies: 21
    Last Post: 04-04-2010, 07:11

Posting Permissions

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