How much neck tension for cast bullets?

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  • Last Post 22 October 2020
Bill2728 posted this 20 October 2020

30-30 single shot. Bore measures a few 10,000's over .308".  I size .310". The neck of fired cases are .311" internal. I use a Lee Collet Die and intend to order an oversized mandrel.  The one that comes with it sizes .305" internal.  That seems to work ok for gas checked bullets but I want to shoot some plain base bullets. I don't want to breach seat so the question is "what size mandrel do I need to order"?

I use either 20:1 or Lyman #2

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John Alexander posted this 20 October 2020

My answer is you don't need a bigger mandrel at all.  Just back off the collet die until the neck is the size you need for your bullet. If your case neck thicknesses don't vary more than .001" this will work fine.  Most good quality brass will meet this requirement. I know this isn't according to Lee's instructions but there is no good reason to have extremely consistent case neck IDs. 

If the loaded cast bullet round chambers freely just enough tension to keep the bullet from falling out or being pushed back in while in your pocket will do.  If you are pressing the bullet into the throat or want clear land marks on the nose of a bore rider, you can determine how much is enough by trying dummy rounds so a round can be chambered without pushing the bullet back in the case. Of course you can't try different case neck IDs if you are pressing the neck down on a mandrel unless you has a set of mandrels of different sizes -- so it is sort of a catch 22.

The danger of seating anything but very hard bullets in a too small neck ID is damage to the bullets by lead shaving, upsetting to inconsistent diameter or even bending a long bullet.  Are you sure you are getting away with seating .310/20:1 bullets in a .305 neck without damaging the bullet?

Good luck.

For more information read my article "In Praise of the Lee Collet Die" in the July/August 2020 Fouling Shot.

John

 

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Little Debbie posted this 20 October 2020

Check John Alexander’s article in Fouling Shot #266. You’ll learn to adjust your Lee collet die for your preferred inside neck diameter. Great article and will likely save you from ordering a new mandrel.

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Spindrift posted this 20 October 2020

My rule of thumb is; 0,001in for plain base bullets, and gas checked bullets that will not see any field use. For GC bullets meant for field use, I choose 0,002in. 

 

I use the Lee collet dies whenever I can, I love them. Then I set the neck tension, and flare the case mouth, using NOE expander plugs and the Lee universal flaring die. It has worked well for me. 

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Geargnasher posted this 21 October 2020

I do just as Spindrift does, .002" for most gas-checked and .001" for plain-based cast bullets.

I used to do the collet die dance but tension can be a moving target and it won't help ovoid or dented necks much. Know I just make the mandrel size needed in my lathe and stuff a piece of drill rod in the end fir a decapper. Brass springs back off if the mandrel about .001-.002" so it needs to be smaller than what you want your final neck ID to be. I size my powder-coated 30-39 bullets to about .3098" and size the necks hard against a .307" mandrel when I choose the Lee collet die, that ends up with 1.5-2 thousandths interference fit, give or take for variances of neck thickness and state of anneal.

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RicinYakima posted this 21 October 2020

My experience, FWIW, is that consistent neck tension is a factor for match loads. I have always cleaned my match brass every season with 0000 steel wool on a small brass brush. Then every reload, I brush out the neck before neck sizing. And like geargnasher, I make my own M dies.

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JeffinNZ posted this 21 October 2020

Don't size the bullet at all.  If the fired case is .311 then match the bullet to that.  My .30/30 bolt gun will chamber a .312 bullet in a fired case and SHOOTS with it. 

Cheers from New Zealand

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John Alexander posted this 21 October 2020

I have great respect for Ric, and he wins his share of matches. I used to clean inside the necks as he does.  But just to balance the opinions here a bit, I probably haven't cleaned the necks of my match brass (or any other) in twenty years.  My current lot of 300 cases used in matches is on it's 61st reload and has never been cleaned in or out except for wiping the smoked necks off.

My peculiar practice, or lack thereof, hasn't seemed to put me at a disadvantage against competitors most of whom i assume clean necks.

A lot of thoughtful shooters think neck tension is always zero because the neck expands leaving no contact with the bullet before it starts to move. Something more to ponder.

John

 

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John Carlson posted this 22 October 2020

Since my bullets are engraved by the rifling when chambered, I agree that neck tension has little effect on when the bullet starts to move.  It could however significantly influence how far the bullet slides into the rifling and in that respect, consistency could be important.

Holding public office should be viewed as an obligation to serve, not an opportunity to rule.

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max503 posted this 22 October 2020

Good thread.

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45 2.1 posted this 22 October 2020

Brass has the property to spring back proportionally to the hardness it exhibits. Depending on how tight or generous your chamber neck is a lot of things can happen. Fully annealed case necks can give poor accuracy when the neck clearance is greater than a thousandth. A case neck that tinks when flicked with a fingernail can provide enough guidance for the rifle to shoot well also. Accuracy is determined on how concentrically the bullet is delivered into the rifling. The amount of neck tension used really depends on whether you damage the bullet (by distorting it or sizing it down) while seating it.

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