Bolt nose recess depth
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  1. #1
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    Default Bolt nose recess depth

    I can't understand what Brownells is trying to say in note 4 where is says "Minus Dim. C from A plus 0.010 and this will give you the depth of the 0.708 cut."

    http://www.viperbench-rest.com/Remin...Directions.PDF

    It seems to me that if the shank length is already 0.010 short of the lugs (from Note 2), then the recess depth at the difference between dimension A (depth to lugs) and C (depth to bolt ring) would already have .010 clearance to the bolt ring.

    Saying "Minus C from A plus 0.010" is confusing as heck. Why is there even the .010 in there? Now the clearance will be .020 total if I am thinking this through correctly.

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    You need to have .005 clearance on all surfaces. If a bristle from a cleaning business breaks off, you want the rifle to still work. When you screw a barrel on to the action the shoulder sets back .002, that's why you have to leave a little extra room on your go gauge. I make my bolt nose recess a little deeper to allow for this.

    Sent from my Pixel 2 using Tapatalk

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  4. #3
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    Quote Originally Posted by Grizzlypeg View Post
    I can't understand what Brownells is trying to say in note 4 where is says "Minus Dim. C from A plus 0.010 and this will give you the depth of the 0.708 cut."

    http://www.viperbench-rest.com/Remin...Directions.PDF

    It seems to me that if the shank length is already 0.010 short of the lugs (from Note 2), then the recess depth at the difference between dimension A (depth to lugs) and C (depth to bolt ring) would already have .010 clearance to the bolt ring.

    Saying "Minus C from A plus 0.010" is confusing as heck. Why is there even the .010 in there? Now the clearance will be .020 total if I am thinking this through correctly.
    The way I read it, the .010" is subtracted in step 2, and added in step 4 to maintain the .010" clearance. I cut them between .005" and .010" depending on the intended use of the rifle. Never less then .005".

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    A-C= Counterbore depth
    A-.01 +/-.002= Tenon length

    You are correct, once you’ve established your tenon/lug face clearance, it is already built into your counterbore.

    The counterbore and lug/tenon clearance is not a critical dimension, as long as there is some. If there’s at least .005” clearance on everything once it’s assembled, function will be fine. Loosening those clearances will not affect function or accuracy at all. You could eliminate the counterbore and have a flat breech face and it would also still function, but you’d lose about .150” of thread engagement.

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    That form is a great help to get started, but it doubles the .010” like you’ve stated. .005” is a min in my book. If you ever get a piece of powder in there, it won’t close. Nothing wrong with the .020” it gives you. I use .005” for br stuff and .010” for hunting rifles. My buddy used .025” and he’s been building rifles for 30 years. No difference at the range in our tests.

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    Thanks. All done. Might have time to take it to the range tomorrow and see how it shoots.

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    I laid an imaginary one out using their work sheet and the two dimensions in question, the shank plus lug with bolt lug clearance, and the bolt nose clearance at the bottom of the counter bore, are two different calculations and the dimensions do not stack. Using this worksheet one would wind up with .010" clearance at both places. It is confusing the way it is written out on the sheet, but it works.


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