Runout???

[gohring3006]

What if you were getting 4-5 thousandths at the case neck and 4-8 thousandths at the bullet ogive. Where would you start to look for a culprit. I'm getting 2-3 thousandths at the case neck with a FL die and a neck die.

 

[Mikecr]

The root cause of runout is thickness variance in cases(which runs web to mouth).
It's brought into play with sizing cycles. The greater the thickness variance, and sizing of it, the greater the runout.
If you want to reduce runout, you go after these.
Simple

 

[FearNoWind]

4-5 thousandths at the case neck and 4-8 thousandths at the bullet ogive.

Looks to me like you're taking runout measrements post seating. Check the neck runout before seating, then again after seating. Forget about the bullet runout for this test. It may tell you where the culprint lives. Bullets that don't seat poperly will read off center at the ogive and at the neck.

 

[gohring3006]

Looks to me like you're taking runout measrements post seating. Check the neck runout before seating, then again after seating. That may tell you where the culprint lives.

I'm going to mess with it later, and do just that.
Do you think the neck runout is amplified at the ogive, and that's why I'm getting up to 8 thousandths there?
I really need to determine the culprit first right?

 

[FearNoWind]

I'm going to mess with it later, and do just that.
Do you think the neck runout is amplified at the ogive, and that's why I'm getting up to 8 thousandths there?
I really need to determine the culprit first right?

i like what Mike had to offer with respect to the uniforming of neck thickness. That will become apparent when you run the pre-seating/post seating tests. Post seating irregularities are rarely attributable to the seating die or the seating process. Most commonly they identify the lack of uniformity in neck thickness. So if the results point to post seating irregularities it's easy enough to turn the necks, reseat, and see if neck thickness is the problem. If it isn't, then I'd look at the seating stem.
Ain't it fun trying to figure out some of this stuff?

 

[gohring3006]

The root cause of runout is thickness variance in cases(which runs web to mouth).
It's brought into play with sizing cycles. The greater the thickness variance, and sizing of it, the greater the runout.
If you want to reduce runout, you go after these.
Simple

I was worried about that. I am purchasing a next turning tool soon hoping it will help.
But running web to neck is incurable.

 

[cape cove]

Alot of time case neck run out can be caused by the spindle assembly in your size die not being properly adjusted. Try sizing a case with the spindle removed and check your case neck run out. If it's ok then try with the spindle instaled. If it's not good then you have found your problem. This very thing happened to me a while back.

 

[Frank in the Laurels]

Unless your bench rest group shooting I wouldn't get to excited about it....in the hunting world it matters not, unless your trying to eye shoot one at 300 yards...neck turning on an already sloppy neck will worsen the problem and if the gap is too big cause your necks to split...

 

[MudRunner2005]

I was worried about that. I am purchasing a next turning tool soon hoping it will help.
But running web to neck is incurable.

Just remember to make sure you don't accidentally order the Ike Turner...Like you said, it might beat your brass up too much.

 

[gohring3006]

Hahahaha that's right Mudd.

I'm thinking I can't really measure my necks unless they are uniform. So I'm going to turn the high spots off the necks.
I am going to try sizing without the expander ball, among other things.

 

[Gene]

I am going to try sizing without the expander ball, among other things.

Now you are on the right track. Turn the necks slightly. Get a good bushing die with proper size bushing, and your run out will diminish. Expander balls are notorious for pulling necks crooked.

 

[Mikecr]

[thickness variance]running web to neck is incurable.

You can measure thickness variance(which carries full body length) at necks, to cull out the offenders. Where you get only 5 per 10 having little variance -you see a price for cheap brass. But it can all balance out to gain if you have a plan to make your brass last.

While an expander ball contributes to runout, you won't reduce loaded runout without neck pre-expansion. This drives what thickness variance you have outward -away from seating bullets.
To pre-expand without a big hit in runout use an expander mandrel with a Sinclair or PMA expander die system. If your intent is to turn necks might as well use Sinclair or PMA neck turning systems along with this. But if your neck clearance is already high, turning will add to your sizing, and while runout is mitigated here, work hardening of necks is still there as an issue. In this case, plan to process anneal at a rate saving your brass.

 

[gohring3006]

You can measure thickness variance(which carries full body length) at necks, to cull out the offenders. Where you get only 5 per 10 having little variance -you see a price for cheap brass. But it can all balance out to gain if you have a plan to make your brass last.

While an expander ball contributes to runout, you won't reduce loaded runout without neck pre-expansion. This drives what thickness variance you have outward -away from seating bullets.
To pre-expand without a big hit in runout use an expander mandrel with a Sinclair or PMA expander die system. If your intent is to turn necks might as well use Sinclair or PMA neck turning systems along with this. But if your neck clearance is already high, turning will add to your sizing, and while runout is mitigated here, work hardening of necks is still there as an issue. In this case, plan to process anneal at a rate saving your brass.

Good info, I do anneal with Tempilac and a torch. It seemed to help with neck tension.
I have the RCBS case master and measured several sonic cleaned brass and found you are right about the full body variance.
That case master has caused some "lost in thought stares" and a little less sleep.. Lol

 

[Mikecr]

On more thing; When you FL size thickness variance it causes outright bananas, and all the neck work in the world will not really help.
Variance, and sizing of it..

Whether it matters to results depends on chamber clearances. If high, runout matters less, even while this leads to greater sizing -which leads to greater runout. A cause/affect loop that is fortunately forgiving.
Where clearance are tight, you can produce truly straight ammo. But where you've caused/introduced runout anyway, you're more likely to see degrading performance from chambered tensions. A case pressing a point hard in a chamber is just the same as pressing hard against any other part of the metal system. It throws shots.

It's a reason some folks see FL sizing as practically required. But it isn't always. We can make straight ammo, with less effort, that shoots fantastic, where a well implemented plan reduces or eliminates sizing requirements. Another cause/affect balance. Just takes an early plan.