Neck tension conundrum.

[Just Dave]

I recently ran 25 NEW Lapua cases thru a NEW rifle, testing a few loads where I thought the ideal speed should land. Came up with a nice grouping, and proceeded to prep cases for further dialing in of load. Picked a .272 bushing out , based on neck wall thickness, should have given me about 2-1/2 thousandths neck tension. With only 1st firing, I didn't need to set back shoulder, so I went to town, and ran all 25 cases thru, using same technique as I always have,
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Upon final inspection, I went thru all 25 cases, testing to see if any of the cases sprung back further than others, by slipping a sample bullet into the neck to confirm resistance.
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I have 12 out of the 25 cases that the bullet ( multiple samples tried) will hang up a little right around top of case neck , then easily slip further in, until it hits the bottom of the neck.
it can be easily pulled in or out, but would require force to seat it any further than bottom of neck.
( Which is too short )
The other 13 , have resistance to bullet right at top of case, and seem to be "normal"
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It is almost as if the neck has a "bulge" with only the top and bottom having contact with the bullet.
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I've been doing this awhile, but I am stumped.
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I am using RCBS gold Full length-bushing die, I skipped annealing this time, as they were all new cases.
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I tried switching the bushing down to a .270 , with no change in tension
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Ideas ?

 

[savagedasher]

Did you Chamfer the neck with a vld tool ?
Larry

 

[alb]

How are you measuring the neck wall thickness?

 

[jonbearman]

Sounds like it is newer lapua brass which isn't quite as thick in the neck wall so you will have to do what I did and go to a smaller bushing in order to obtain some neck tension. What was your chamber reamed for such as no turn neck or a .270 neck or what? Spring back depending on the actual hardness I have seen is more than .001 inches so with that in mind I would use a .266 like I am currently doing myself so I end up with about .003 tension which works well in my current rifle.

 

['Freak]

What’s the fired case neck outside diameter before any resizing?

What’s the case neck outside diameter after resizing using the .272” bushing?

What’s the case neck outside diameter after resizing using the .270” bushing?

What’s the case neck outside diameter after seating a bullet?

 

[Just Dave]

Dasher - Yes VLD reamer,
alb- with a ball-end mic, taken at various positions, all about .0145 thick
jonbear- I think you might be unto something, I run Lapua brass in my 30-06, and I know the wall thickness on that is about .018-ish ,, I think I picked out and ordered my bushings based on that assumed measurement.
Freak - .2745, so it's not a tight chamber. And I didn't measure outside, I kept looking to the inside , and it seems to not change from .2435, with some really loose one's at .2440.
But that only seems to be getting a reading from the top and bottom of the case neck.. . .
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Here's something really weird ,, I read the INSTRUCTIONS ( Shhh, don't tell my wife) , and it stated that it came with an expander ball, for " preparing new brass" and that I needed to swap it for the other "non-expanding" "ball" (more like a straight shank) in order for my neck bushings to work correctly..
Well the "non-expanding" straight end RCBS says to use only measures .200" in diameter .. expander-type measures .242-ish.
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A call to RCBS is in order ,, I don't understand how a .200" diameter ball supports any part of the case during neck sizing , it's not even close enough measurement to say it "guides" it as the neck bushing squeezes.

 

['Freak]

Be rid of that .242-ish expander, the .200” is just a placeholder that otherwise isn’t supposed to do a thing.

 

[Ringostar]

If you have .0145 neck x2 plus .244 = .271 for a loaded round. You might want to try dropping down to a .269 bushing. Also the small expander is to hold the depriming pin, and not interfere with your neck size when drawing the case out of the die.

 

[Shynloco]

Dave,
I am unclear from your post if you FIRST fireformed the brass or was this the brass' maiden shoot. Also remember, it could take a couple hundred rounds through a new chamber to settle in as well. Know that new Lapua brass also needs to be shot a few times before it settles in meaning it needs to experience the expansion/bounce back effect. And that also means you CAN experience a difference of about .02 in your measurements until the brass "is broken in." Further, I've experienced exactly what you described and "cleaned up the brass" (light turning) AFTER it's first firing and then the necks settled in with better concentricity than just pure brand new brass. But you have little choice as to the bushing size you use, not to mention your chamber (custom tight or SAMMI spec) has a definite impact on the expansion of the brass. SO your combination of a new chamber and new brass leave you with several variables until both settle in. Just my .02 worth of ideas.

Alex

 

[Just Dave]

Also the small expander is to hold the depriming pin, and not interfere with your neck size when drawing the case out of the die.

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Thanks for that bit of info,, I kept looking at it, thinking they sent wrong part or something..

 

[Just Dave]

Dave,
I am unclear from your post if you FIRST fireformed the brass or was this the brass' maiden shoot. Also remember, it could take a couple hundred rounds through a new chamber to settle in as well. Know that new Lapua brass also needs to be shot a few times before it settles in meaning it needs to experience the expansion/bounce back effect. And that also means you CAN experience a difference of about .02 in your measurements until the brass "is broken in." Further, I've experienced exactly what you described and "cleaned up the brass" (light turning) AFTER it's first firing and then the necks settled in with better concentricity than just pure brand new brass. But you have little choice as to the bushing size you use, not to mention your chamber (custom tight or SAMMI spec) has a definite impact on the expansion of the brass. SO your combination of a new chamber and new brass leave you with several variables until both settle in. Just my .02 worth of ideas.

Alex

First time fire-formed, so it is new, .. I will try the smaller bushing sizes, and see how it reacts..

 

[Just Dave]

Seeing as how I have over-worked this brass a little , would it be a good idea to anneal before trying to resize AGAIN ? with different bushing ?

 

[alb]

Annealing certainly can't hurt if it'll give you peace of mind, but comparatively speaking (I anneal right between the part where the neck splits and I throw the case away), I'd think you to be some distance still from over-worked.

 

[243winxb]

Remove bushing , size fired case. Measure neck before and after.

The hole in the die that the neck goes through, shoulder/neck junction, could be to small. Post sizing before the neck even reaches the bushing.

For a 243 Win i use bushing of .270" , .269" and .268"

Measure the OD of the loaded rounds necks with a micrometer. Find the one with the smallest measurement. The bushing should be .002" smaller or more.

 

[500Stroker]

Buy a Whidden full length bushing die, throw away the button and resize. Enjoy

 

[Just Dave]

Upon further inspection .. ( I borrowed my wifes reading glasses) , I see my tube mic. was off "0" about a half.. I reset it to zero again, and now am getting .014- .0135 wall thickness.
I simply bought the wrong range of bushing sizes, got a .269 and .268 on the way.. .
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