Expanding/turning necks - 6.5-284 L brass

[jvw2008]

When converting 6.5-284 Lapua Brass to the 284 neck. Is it best to turn the necks before or after running them thru the 284 expansion mandrel to minimize a loss in neck concentricity?

 

[Cowtownup]

Expand first and then turn...

 

[ShootDots]

When converting 6.5-284 Lapua Brass to the 284 neck. Is it best to turn the necks before or after running them thru the 284 expansion mandrel to minimize a loss in neck concentricity?

One of the main reasons for neck turning is to "even out" the neck thicknesses that vary around the neck. What better way than to neck UP, thus REALLY pushing all the inconsistencies to the OUTSIDE of the case neck wall where they can be turned off? Neck UP, then turn the necks. NOTE: make sure that you cut a small amount, maybe 1/16th of an inch into the shoulder. Necking up creates a thick "bump", for lack of better terminology, right at the neck / shoulder junction>>>this needs to be turned off..

 

[jvw2008]

@BoydAllen: thanks for the PM. The info you sent was helpful.
Traditionally I don't turn necks until after the first firing. This batch of 6.5-284 Lapua brass has more variance in neck thickness than I expected (0.0145-).)16). I selected two cases with almost no runout, lubed the inside of the necks with Imperial wax and did successive passes over a .262 and then a .282 PMA expansion mandrel. Once expanded, each case had a neck runout of approximately 0.020. Most of the loss of concentricity occurred with the pas over the PMA28 mandrel.

I usually leave the expander mandrel just a little loose in the die so it can follow the neck. Is that a mistake?

Boyd you suggested using a liquid lube - are you referring to something like a motor oil?

I will try the gradual multi-pass technique you described - it makes sense.

@shootsdots: Hey

 

[jvw2008]

Whoops hit the wrong button on the keyboard. Hey Dots - long time no talk! The reason I was considering turning first, centered on the thought that during expansion of the neck the thinner part of the brass might be stretching more than the thicker part leading to a loss in concentricity. Frustrating problem and I was reaching for straws to explain what was occuring.

 

[ShootDots]

Whoops hit the wrong button on the keyboard. Hey Dots - long time no talk! The reason I was considering turning first, centered on the thought that during expansion of the neck the thinner part of the brass might be stretching more than the thicker part leading to a loss in concentricity. Frustrating problem and I was reaching for straws to explain what was occuring.

You are correct! That is PRECISELY why I have all my reamers spec'ed to where I HAVE TO turn them down to a 12 thousandths neck wall thickness>>>>>it forces me to cut and clean up the necks to a virtual 100 pct. clean up! NOW the necks are even all the way around! Additionally, once annealed after firing, the bullets seat like smooth butter!

 

[BoydAllen]

If you do not have a one piece FL die, so that you can size the neck all the way to the shoulder, I would expand the new brass. There are a lot of liquid case turning lubes. That is what you want. Go for the best film strength, either Case Lube II which is water based and therefore easy to remove, or one of the oils. To do what I messaged about you need a special expanding up mandrel with a long taper. My experience has been that the Bonanza press is not what you want for expanding up. I have tried that. I use a soaked Q tip to apply the lube to the inside of the necks and for the first one to the mandrel. Using the right stuff and my press technique I have expanded .220 Russian necks, that started out with .002 runout, up to 6mm with no increase, but it does require paying strict attention to what you are doing and some practice, monitored with a concentricity gauge, to get the technique down. Before I got the right type of mandrel, and came up with the right technique, I could not get anywhere near my current results. In the past I have played with every conceivable combination. What I told you was the end result of a lot of trial and error.

 

[jvw2008]

The PMA expansion mandrel I am currently using does have a gradual taper. Boyd do you let the mandrel have a little play in the die or do you snug it down?