Concentricity .. how important?

[bigedp51]

The reason so many reloaders use a body die and the Lee collet die is because it produces less neck runout than a bushing die. A bushing die works best with tight neck custom chamber and not reducing the neck diameter over .004.

I'm just not a fan of the Lee collet die and prefer using the Forster full length benchrest dies and seating dies. And if needed Forster will hone the dies neck to your desired diameter. Below the "6.5 Guys" are switching from bushing dies to honed Forster full length dies.

Weekly Gear Update – Forster Honed Dies
http://www.65guys.com/weekly-gear-update-forster-honed-dies/



Bottom line, if you remove the expander from a full length die and size a case it will be as concentric as it ever will be. The problem is if the expander is not centered on the down stroke of the ram and if the neck is pulled off center. And the Forster high mounted floating expander can not pull your case necks off center and induce neck runout.

This is where having concentricity gauge comes in handy and finding out if the problem is the sizing die or seating die.

I prefer to sort my cases with the Redding neck thickness gauge, and one twist of the wrist will show the amount of neck thickness variations and the uniformity of the case.

 

[tbrice23]

Forster honed FL die is a great idea... but

This needs to be said,
If you remove your expander your sizing the neck will too small for bullet seating bullets smoothly without inducing more run out, too much seating force.

And it will over work the brass necks.

 

[bigedp51]

Forster honed FL die is a great idea... but

This needs to be said,
If you remove your expander your sizing the neck will too small for bullet seating bullets smoothly without inducing more run out, too much seating force.

And it will over work the brass necks.

My point being it is the expander that can induce neck runout if the expander is not centered. "AND" the 6.5 Guys were getting less runout with the Forster dies and their high mounted expander than a Redding bushing die. And Forster recommended sizing the neck .004 smaller than a loaded round and use the expander on their honed dies. And Redding recommends about the same amount with their bushing dies if the necks are not turned and use the expander that comes with the bushing dies.

At the Whidden custom die website they tell you they get the most concentric cases from non-bushing full length dies. And at the Whidden site they also sell expander kits with five expanders from bullet diameter to .004 under bullet diameter.

This is where a neck thickness gauge and a runout gauges comes into play, and finding out what is causing the runout and fixing the problem.

 

[Rich Coyle]

Forster honed FL die is a great idea... but

This needs to be said,
If you remove your expander your sizing the neck will too small for bullet seating bullets smoothly without inducing more run out, too much seating force.

And it will over work the brass necks.

You are forgetting the die can be honed to the desired diameter. There's no more force required than with a bushing die.

 

[tbrice23]

I said honed Forster die.

 

[Clark]

I did an experiment with 25 pieces of brass each dedicated to one sizer die.
The result was the opposite of what I expected for results.
The cheapest and ugliest Lee Collet neck die was the best, and the Redding FL "S" die was the worst , with all the other dies in between.

For the last 15 years for each new cartridge I have got a reamer, a honed Forster FL die, a Forster Sliding seater die, and a Lee collet neck die.

My technique has been stuck until 2018 when my brother sent me a #3 Morse Taper 3 jaw chuck live center for the lathe. I can now quickly and easily turn necks with no measurable [with a ball micrometer] run out. This makes little difference with most cartridges, but it will be a big deal with case forming, like converting 308 Lapua Palma brass with small primer pocket to 260 Remington.

This week I have honed out [my own caveman honing] a couple Lee 280AI FL necks from 0.298" to 0.308".

This thread got me to order Redding body dies for 280AI and 7mmSTW.

 

[gte901m]

I did an experiment with 25 pieces of brass each dedicated to one sizer die.
The result was the opposite of what I expected for results.
The cheapest and ugliest Lee Collet neck die was the best...…...

Similar experience. Reloading is like unraveling a sweater - it never ends.

I started testing different FL dies with two batches of brass: one w/ uniformed necks (skim turned) and one virgin. Initially, concentricity was basically the same. After a few firings/loadings, concentricity flyers started appearing in both test groups. This lead me to believe something else was causing problems. All FL dies performed about the same.

Next I hypothesized case wall thickness could be causing problems. I used the RCBS concentricity tool to segregate new brass into groups of <=1 thou wall runout and >4 thou. Skim turned necks on both groups. After several firings, the >4thou wall variance group had more concentricity outliers than the <=1 thou group. Similar results across several FL dies. This led me to believe wall thickness variance was causing problems. My theory was brass flow during firing and resizing was not uniform, since wall thickness was not the same. Sure enough, after several firing, necks which began as uniform thickness (skim turned) were no longer uniform.

I ordered a set of pin gauges, and began measuring inside neck dimension of sized causes. This was a eureka moment for me. In a FL die, any thickness variance is pushed toward the ID when FL sizing. With pin gauges, you could feel this - pin would drag on one side. This was after the expander had pulled back through the neck and supposedly made it round. I then noticed (with pin gauges) after several firings, that donuts were developing at the inside neck/shoulder junction for all my brass. In my mind, its impossible for an expander to pull back through concentric when it encounters a non-symmetrical donut and a non-symmetrical neck.

Then came inside neck turning. It helped reduce FL sizing concentricity. Uniform wall thickness still produced more consistent concentricity than >4thou wall thickness. Inside neck reaming fired brass to remove donuts and skim turning necks produced the best results for all FL dies.

Then came honed and bushing dies without expanders. Similar results. Donuts don't cause concentricity issues while sizing, but due when seating a bullet. Sill have to ream donuts and turn necks for best results.

Finally the body/collet setup. I still inside neck ream to remove donuts, but don't turn necks. The collet die produced the most uniform ID of any die, which I believe maintains concentricity when seating a bullet and uniform bullet tension.

 

[Clark]

The Redding body die for 280 Ackley arrived and the neck is a 0.320" go 0.321" no go