expander die increasing neck run-out?

[Cakes]

Just started to prep some new Lapua 6.5/284 for my straight .284. I have been using a well known expander die in the past and don't recall having this problem. Fresh brass with a neck thickness variation of 1-1.5 thou. and a neck run-out of 1-2.5 thou. Lube the die and neck inside well, lightly chamfer inside neck and after expanding the necks I get a run-out of 3-6 thou. Majority of expanded necks have a run-out of 4-6 thou. I do turn them down to .014 thickness but still end up with a non-fireformed load that has a run-out of 3-6 thou. which is not acceptable for me on the 1k line. I do run them thru a WTC die to get the final neck sized but that does little to straighten out the neck. Can't recall if I had this problem before fireforming as my old lot of brass (300) has all been fired 12-15 times with annealing. Am I missing something, having a senior moment??? I realize that once fireformed I'll be back to my usual .5 thou run-out but I hate to waste all those components fireforming. Thanks, Eric in DL

 

[ShootDots]

I do not use a die for expanding necks. I use a carbide expander mandrel... You can not get much straighter than with a mandrel..

 

[Jeff Von Rosenberg]

Doesn't a expand real mandrel go inside if an expander die?

 

[ShootDots]

I used to use a "regular F/L" die with a tapered expander button to expand my brass for my .358STA.. That may be what the OP is using...

 

[Cakes]

To clarify things....I use a carbide expander mandrel that fits inside of its associated "mandrel die". This mandrel free floats a small bit inside until it hits the top cap of the die. Thanks, Eric in DL

 

[BoydAllen]

IMO, if the float allows the mandrel to tilt, that is not good. What lube are you using to expand with?

 

[ShootDots]

To clarify things....I use a carbide expander mandrel that fits inside of its associated "mandrel die". This mandrel free floats a small bit inside until it hits the top cap of the die. Thanks, Eric in DL

Unless the mandrel die is not sitting square with the press, I don't know. It sounds like you are using the Sinclair mandrel die and mandrel... If so, that is what I use and I don't experience any problems.. Maybe someone on here has experienced that same phenomenon and can tell us what's wrong and how to fix it..

 

[lawrence97]

What press are you using?

I had the same issues as you after sizing and neck turning for my 284. I shot it like that and once the brass was fired the runout went away!

I was told that the coax press was allowing the mandrel to float and cause the runout. I was also told this was normal and that I just needed to shoot and it would sort itself out. I decided to just shoot and the rifle hammered during development with new turned brass as well as once fired. After that I just checked the runout after the brass had been fired once or twice.

 

[BoydAllen]

I tried a friend's Coax for expanding .220 Russian brass up to 6mm. That will be the last time that I use one for that. The results were ugly as far as runout goes. The best that I have gotten is with a Harrell Combo press. It has a one piece frame that is produced excellent alignment between the ram bore and the die threads, and the threads are much tighter fitting than those of my Rockchucker, which produces adiquate results, but not as good as the Harrell.

 

[Erik Cortina]

Just shoot the brass. I have shot ammo with .015" runout and it shot great.
Necks will be straight after fire forming.

 

[artbosco]

If an expander die is increasing run out, then an explosion within your chamber [assuming it's straight] that produces 50,000 to 60,000 psi will easily straighten them out.

 

[Cakes]

I appreciate all the comments. Yes it is a Sinclair and I use several (6) Rockchuckers that have served me very well over the years. Once fired my run-out is usually under .0005 but I am glad to hear Erik has had satisfactory results with up to 15 thou. of run-out. This particular Rockchucker is the last one I added before switching over to a WTC die (+++) and I'm thinking that the die/mandrel is not perfectly square with the shellholder/piston of press. Too much time worrying about a couple of thou. run-out that for new brass is probably no big deal. Thanks, Eric in DL

 

[fdshuster]

Cakes: I'm agreeing with those who say, load new brass and fire it. The vast majority (if it's excellent brass to start with) will straighten with the first firing. You may get a few that will never straighten, no matter how many times they are fired. They were defective when they left the factory.
You proved that when you said, "Once fired my run-out is usually under .0005".

Mark them and use them for non-essential firing, like close range, non-match, first round foulers, basic scope sight-in, etc.

 

[Ares]

Use a harrels turret press, and 21 st century die/mandrels. Expanding necks on my 284 win, and it gives excellent results, with very little runout.
But if someone is looking for a press with super precise alignment, and machining take a look at the Turban cnc presses.
It's a work of art and guaranteed centering accuracy, of 0.00039370 (1/100 mm) inches for the whole stroke length.
They are completely CNC milled from solid blocks of steel, to very precise tolerances so they do cost a lot of money.
Had one for a few months now and it's truly a work of art, and the last single stage i will ever buy.

 

[Shynloco]

Cakes: I'm agreeing with those who say, load new brass and fire it. The vast majority (if it's excellent brass to start with) will straighten with the first firing. You may get a few that will never straighten, no matter how many times they are fired. They were defective when they left the factory.
You proved that when you said, "Once fired my run-out is usually under .0005".

Mark them and use them for non-essential firing, like close range, non-match, first round foulers, basic scope sight-in, etc.

Add me to this group...shoot it and let the chamber straighten it out. If it's not right after that, it's the brass and you might consider using those pieces as foulers. Some of my shooting partners even trash can them (even being new brass). Been there...done that.

Alex