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Chamber length, and trim length question

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  #1  
Unread 06-10-2010, 11:37 PM
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Chamber length, and trim length question

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.
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  •   #2  
    Unread 06-11-2010, 04:37 AM
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    Re: Chamber length, and trim length question

    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.
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      #3  
    Unread 06-11-2010, 02:57 PM
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    Re: Chamber length, and trim length question

    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.
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      #4  
    Unread 06-11-2010, 04:43 PM
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    Re: Chamber length, and trim length question

    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
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      #5  
    Unread 06-11-2010, 09:26 PM
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    Re: Chamber length, and trim length question

    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.
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      #6  
    Unread 06-11-2010, 09:43 PM
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    Re: Chamber length, and trim length question

    Quote:
    Originally Posted by Firearrow View Post
    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.


    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/arti...ng-range-1.php

    Last edited by jimbires; 06-11-2010 at 10:16 PM. Reason: more info .
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      #7  
    Unread 06-12-2010, 12:37 AM
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    Re: Chamber length, and trim length question

    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.
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