Chamber length, and trim length question

Discussion in 'Reloading' started by Firearrow, Jun 10, 2010.

  1. Firearrow

    Firearrow Well-Known Member

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    Just wanted to run this past you guys. This is the first time I am messureing the chamber length, and then using this info to let me know when it is time to trim my cases, and I didn't want to blow up my rifle, or kill my self. Unless this method is way off course, and if so plese point me in the right direction.

    1. Chamber length for my factory Rem 300 Mag is 2.6515. I got this buy using the sinclar chamber length case plug. Messured from the bottom of the case to the end of the plug after chambering the case/plug.

    2. My average length case that has been fired once is 2.615.

    3. My book tells me to have a trim length of 2.610. Now I know this length will allow my to chamber this into any rifle with out having the end of case sit on the rifling.

    So here is the question. After each time I reload my brass I need to make sure that the length of the case does not exceed 2.6515, and if it does I need to trim it back a little. ****DO I HAVE THIS RIGTH, OR AM I GOING TO KILL MY SELF****?

    4. If I have this senario right, how much should I trim off of the case once the case length is greater than 2.6515?

    Thanks for helping out a new guy.
     
  2. Gene

    Gene Well-Known Member

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    Its not likely that your brass will ever exceed that length. The danger in having case length excessive is that when chambered, the mouth will crimp up against the bullet, increasing chamber pressure. Most modern rifles will handle it, but there is always the chance that you could have a problem, particularly if your load is on the high size.

    I trim about .005 or .010" below SAMMI recommended length, check it every couple reloads. Trim more than that can encourage a carbon ring build up in the chamber just where the mouth ends. Carbon ring is not dangerous, but can be hard to remove.
     

  3. Mikecr

    Mikecr Well-Known Member

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    I would not trim to 2.610 unless that is the only way you can get em consistent. You are already way too far from chamber end. As gene said carbon will build up in front of the mouths, and you'll probably have some excess case sooting.

    This was a good check on your part though.
     
  4. jimbires

    jimbires Well-Known Member

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    I'm using about .025 clearance .


    so if your chamber is 2.6515
    less clearance - 0.025
    trim length = 2.6265
    I would round this off to 2.625
     
  5. Firearrow

    Firearrow Well-Known Member

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    Ok I have either 2.625 or 2.642. It's friday and lets have some fun. Who votes for 2.625, and who votes for 2.642. I am to new at precision reloading to have an informed opinion. So what does everyone think.
     
  6. jimbires

    jimbires Well-Known Member

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    where did you get 2.642 ?

    ok , I see . Gene said he trims .005 - .010 shorter than SAMMI
    I was a little afraid to push the clearance that much . that's why I have .025 . in the article Tres says to just trim short of this measurement . looks like I'm still trimming to much .it will take you awhile for all the brass to grow to this measurement while all being trimmed to an even length . here is the article clip .
    To use a gauge like this:
    1. Thoroughly clean your weapons chamber.
    2. Take a scrap case and trim it WAY back with your case trimmer, say .050" SHORTER than book spec.
    3. Seat your plug gauge into the case - long.
    4. Ease this round into your weapon and fully close and lock the bolt.
    5. Remove the case gently without bumping the gauge. It has hit the end of the chamber and be pushed back into the case by the action of locking the bolt.

    Measure the overall length of the case, head of the case to end of the plug, and note that measurement somewhere obvious and permanent in regards to loading for this particular rifle. It would probably be a good idea to repeat this measurement three times and average all three readings.

    Now until this dimension changes (barrel removal, etc.), trim your brass just short of this measurement instead of “book trim to” specs.

    Once we have our cases all trimmed to a uniform length for our specific rifle we now need to deburr the mouth of the case.


    here is the article link
    http://www.longrangehunting.com/articles/hand-loading-long-range-1.php
     
    Last edited: Jun 11, 2010
  7. Firearrow

    Firearrow Well-Known Member

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    Yup. That is how I got my chamber length. I just need to know what to trim my cases too. My first post has my chamber length, recomended trim length per my reloading manual, and average case length that has been fired once. Like I said new to the game, I just want to do it rigth from the start.
     
  8. jimbires

    jimbires Well-Known Member

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    I have one rifle that I do this with , it's a factory rifle . the only reason I checked this rifle is I have a big gap between my shell holder and full length die to just bump my shoulder back a couple thou. so I wondered what the chamber length was . I got my notebook now so I have the correct specs for this gun . here is what I have
    book max length 2.035
    book trim length 2.025
    my chamber length 2.072
    my trim length 2.050 ( I try to use even numbers )



    I see where I should be safe to allow my brass to go to 2.062 trim - 2.072 max . I was just afraid to push it I guess .
     
  9. trueblue

    trueblue Well-Known Member

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    I trim 0.020 less than chamber length.
     
  10. Mikecr

    Mikecr Well-Known Member

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    Greater than 5-10thou clearance only decreases sealing, and increases carbon build-up, making chamber length a variable..
    There is no reason I know of to desire this.
     
  11. gunrac

    gunrac Member

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    Sammi specs went out the window once I got my guage. Trim only to uniform all my brass. With my factory chamber, I'll never reach max length anyways. I load a lot of the light and shorter stuff, so any extra brass I can safely use, is a bonus. I consider the 7 bucks for the plug, a great reassurance tool to have.

    Sinclair recommends .024 from max chamber length. From the many reads I've came across on this subject, guy's are using a whole lot tighter tolerance's then that. Some up to .005. That's only the thickness of an avg. beer can. I would consider .010 to .015 as my min. To each his own.

    I'm not real sure if I may be reading to much into this statement....... But, everytime I've taken this measurement, each reading was exactly the same. If you have to take an average of your reading's, you may have another issue.
     
  12. Firearrow

    Firearrow Well-Known Member

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    No I got lucky and got the same messurements, except once when the plug rubbed up against the inside otf the chamber. But that was operator error.
     
  13. Short Round

    Short Round Member

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    I was going to say in the plug's instructions Sinclair says 0.024" below chamber length. I would be confident that they're being conservative too. It's the nature of their business.

    That said I follow their advice.

    Talking theory here, I'm assuming the tighter fit of your brass to the chamber the closer you could go to the actual chamber length as your brass shoulder is nearer to the stop, aka the chamber's shoulder. If you're full length sizing with a lot of headspace my thoughts are that you have more play and movement to worry about. This is probably why the bench rest guns can be run at much closer than 0.024".

    Like I said, I'm talking theory and nothing I've tested or watched or anything.
     
  14. Mikecr

    Mikecr Well-Known Member

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    It doesn't make sense that Sinclair would suggest an extreme clearance from mouth to chamber end. Are you sure they aren't referring to an amount to shorten the neck -for gage usage?