What should be the mandrel diameter for a 223 a Lee collet neck sizer? The new set I bought will not reduce the neck size enough to hold the bullet tight, and I don't think applying any more force will help.

I'd make a phone call to lee. The first few sets I got from them barely left the neck diameter .002 less than the bullet diameter. I sanded those down by putting them in a power drill. The last couple sets I got were sizing the inside of the neck .003 under which is what I prefer for a hunting rifle.
They may ask you to send the die with some brass back to them.
The dies aren't always perfect...but when you get a good set they are wonderful. I'd rather pay 2x's the price and get more consistancy and quality through better materials.

What brand of brass are you using?

I had the same thing happen to me. But, when I tried another brand of brass - they were OK. I measured them and the brand that worked was thicker in the neck.

Expect high variance in Lee products.

As you have discovered, this is one of the weaknesses with the (otherwise ingenious) Lee Collet die.

It is likely that your brass is simply work hardened, in which case the die does not work very well (too low neck tension).

As Kraky described above, one option is to polish down the mandrell with some emory cloth. Lee (in their die instructions) suggest reducing the diameter with .001". Alternatively, Lee will supply an undersize mandrell - call them up and specify the caliber of your die. The extra mandrells used to be $5, but I don't know what Lee charges today.

Although this will not fix your neck tension problem, it is also a good idea to take apart the die. Polish any remaining machine marks, and/or apply the thinnest layer of grease between collet and inner die wall. Ensure mandrell will move fairly freely when installed in die (it needs to self-center during sizing operation). Make sure the slits in the collet are free from obstructions.

Nice die, very cheap, produces straight ammo, but it does have its idiosynchrasies...

- mike

quote:

Originally posted by mho:

..... it is also a good idea to take apart the die. Polish any remaining machine marks, and/or apply the thinnest layer of grease between collet and inner die wall. Ensure mandrell will move fairly freely when installed in die (it needs to self-center during sizing operation). Make sure the slits in the collet are free from obstructions.

Nice die, very cheap, produces straight ammo, but it does have its idiosynchrasies...

- mike

+1

quote:

What should be the mandrel diameter for a 223 a Lee collet neck sizer? The new set I bought will not reduce the neck size enough to hold the bullet tight, and I don't think applying any more force will help.

Usually, Lee hopes to let you attain no more than .002" neck "tension". Smaller than that simply increases the tendency for bullet run-out during seating.

Most mandrells are about maybe 2-3 thou. under bullet size, usually leaving .001-.002" of neck difference. That's plenty unless you are really rough with your ammo. Any neck fit tighter than .003" is a total waste because that's as far as brass can stretch without perminently deforming.

Obtaining good neck fit with the Collet Die requires that work hardened, well used cases, be annealed to restore the ability to form to the mandrel and stay there.

Lee's tolerances on imporant dimensions is quite good. On average, they are fully as good as any others of simular design in my experience.

Lee clearly recognizes that (1) most convential die manufacturers use expander balls that leave some necks tighter than is desirable and (2) than you can reduce the size of the Lee mandrel, but you can't increase it, therefore they ship them with the largest mandrel you are likely to need, thus allowing you to hone it down as needed or simply buy a smaller one fromt them if you're not too handy at that kind of work.

It is true that cases with excessively hard necks come out at smaller inside diameter with conventional dies since the springback is from larger to smaller, whereas the springback with a Lee Collet die is from smaller to larger.

One way to assure fairly consistent inside neck diameter with the Lee die is to make the mandrel somewhat "wasp-waisted". You sand down the upper portion where the collet squeezes the neck against the mandrel, but leave the lower portion slightly larger. That way, the neck is made adequately tight, but is expanded as it slips off over the lower part of the mandrel to a consistent I.D.

If you understand what you're doing, the Lee Collet die is a superb design that is a joy to use.

The next thing I am going to do is Gold plate my Lee Collet dies

There ya go, TNEKKCC, turning $20 dies into $60 dies. Have you no respect for cheapness?

quote:

Originally posted by Stonecreek:

One way to assure fairly consistent inside neck diameter with the Lee die is to make the mandrel somewhat "wasp-waisted". You sand down the upper portion where the collet squeezes the neck against the mandrel, but leave the lower portion slightly larger. That way, the neck is made adequately tight, but is expanded as it slips off over the lower part of the mandrel to a consistent I.D.

If you understand what you're doing, the Lee Collet die is a superb design that is a joy to use.

HERESY! Making an expander type die out of a Lee Collet!

quote:

Originally posted by Stonecreek:
There ya go, TNEKKCC, turning $20 dies into $60 dies. Have you no respect for cheapness?

Where do you get these for $20?

http://www.leeprecision.com/cg...250176678.5259=90707

You could buy the:
Mandrel $4
Collet $9
Collet Sleeve [collar]$4
body $8
--------------------
$25 from Lee spare parts

I don't like the Lee lock ring and O ring anyway. I put on a Forster cross bolt locking ring ~$3 or $4 each, and can be bought in singles in bags of a dozen.




Or you can buy a Lee Collet Neck die for $20.59 from Graf, who has them in stock:
http://www.grafs.com/product/233068

quote:

Originally posted by tnekkcc:
http://www.leeprecision.com/cg...250176678.5259=90707

You could buy the:
Mandrel $4
Collet $9
Collet Sleeve [collar]$4
body $8
--------------------
$25 from Lee spare parts

I don't like the Lee lock ring and O ring anyway. I put on a Forster cross bolt locking ring ~$3 or $4 each, and can be bought in singles in bags of a dozen.




Or you can buy a Lee Collet Neck die for $20.59 from Graf, who has them in stock:
http://www.grafs.com/product/233068

Sometimes you can find the deluxe sets for $28.
It would be simple enough to keep the single die and unload the rest of the die set.