Neck tension on new Lapua brass

Dildobaggins

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I was preping brass today for my 6 creed and have a PMA expander mandrel. I'm looking to get .002 neck tension. All the brass that I have measured with my micrometer is .240. this is virgin brass.

2 questions.

Does virgin brass have more spring back than fired brass? I'm going to measure the expander mandrel when I get home, but every single piece of the 100 pieces is .240 on the dot.

If the mandrel die is the correct size would annealing the brass help with spring back? Forgive my stupidity. I've been doing this less than a year. Have my .223 brass down to a science, but the 6creed is not being so kind to me.
 

918v

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Virgin Lapua brass has almost no springback. I would size down the neck and expand with the mandrel.
 
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CK1.0

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I would just run them thru the mandrel, load and shoot. Then take your measurements off once fired

This.

Virgin brass comes in a state that you will never be able to duplicate again. Just use the mandrel to make seating as consistent as you can and then concern yourself with what you get after it's been fired in and "married" to your chamber.

Post-mandrel, I wouldn't worry about whether the brass lands at .240, .241, or .242 as long as it's consistent and repeatable... just use that number to adjust as needed to get repeatable neck tension that you like going forward.
 

Dildobaggins

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This.

Virgin brass comes in a state that you will never be able to duplicate again. Just use the mandrel to make seating as consistent as you can and then concern yourself with what you get after it's been fired in and "married" to your chamber.

Post-mandrel, I wouldn't worry about whether the brass lands at .240, .241, or .242 as long as it's consistent and repeatable... just use that number to adjust as needed to get repeatable neck tension that you like going forward.
Good info thank you. I measured my expander mandrel and it's .2410 I believe Sinclair's is .242. maybe I'll scoop one of them up and try that.
 
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CK1.0

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Good info thank you. I measured my expander mandrel and it's .2410 I believe Sinclair's is .242. maybe I'll scoop one of them up and try that.

For me, in the quest of achieving consistent neck tension I find it helpful to think of it as not really using any specific magic thing (like a particular sized mandrel)... but more as a whole "recipe" that lands me at where I want to be. For example, with my current brass, after every firing I like: AMP anneal + .268" bushing + .241" mandrel = consitent/repeatable ~2 thou (I think) neck tension.

IMO it's not really about whether you end up with ~1 thou, ~2 thou, or whatever neck tension (and/or a neck ID of .240", .241", etc depending on how one likes to keep track of it), just as long as it shoots, and one can pull off landing at that same amount of neck tension repeatably every load cycle.
 
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ncr92

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How are you measuring the inside neck diameter? What sort of micrometer are we talking about?
 

Dildobaggins

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How are you measuring the inside neck diameter? What sort of micrometer are we talking about?
Using a micrometer. Forgot the name of it. I'll check when I get home. It was given to me by a friend who is a machinist, but I'm sure it's nothing fancy. I've read in the forums that you should use pin guages to correctly check tension?
 

Rocketmandb

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    Always trim and mandrel new brass. Lapua (and many others) will have case mouth edges that need to be taken down or they can cause chambering issues. And Lapua necks are also a little on the small side (higher neck tension), so a mandrel is a good thing here - not nearly as bad as ADG, however.
     
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    ncr92

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    Using a micrometer. Forgot the name of it. I'll check when I get home. It was given to me by a friend who is a machinist, but I'm sure it's nothing fancy. I've read in the forums that you should use pin guages to correctly check tension?
    OK. An ID micrometer is a fairly specialized instrument. To trust it's measurements you would need to ensure that it is accurate and calibrated and that your measurement technique is producing repeatable results.

    I don't worry too much about the exact neck diameter of my sized brass. I use a mandrel 0.002" smaller than bullet diameter and I assume there will be some springback. My sized brass should have a neck diameter of 0.003" less than bullet diameter or thereabouts. If my brass is consistent, that measurement should be consistent and that's what matters.

    If you want precisely sized mandrels, 21st Century makes mandrels specifically for neck sizing. They are available in 0.0005" size increments.

     
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