Case neck has 0.002" runout after neck sizings

[markd657]

Hi all,

I have some questions about case neck runouts in my 300 PRC load. I did the following tests with 2 fired cases:

1. The OD of my fired necks is 0.3400". Runouts of the case neck is measured at less than 0.0005" here. Great so far.
2. After sizing it with the L.E Wilson die and a 0.335 bushing (0.005" delta) and the RCBS Rock Chucker Supreme, runouts are still less than 0.0005".
3. However, when I size it one more time with a 0.332 bushing (only 0.003" delta), runouts are now measured at 0.002".

Would this amount of runout make a difference on target at, say at 1000 yards?
Is there a reason why runouts occur on the second sizing but not the first?
For those running with high neck tension, do you size the neck once or you do in smaller increments to avoid runouts?

Thanks!

 

[Mark611]

What kind of dies are you using? are you using new brass/unfired before turning them?

 

[shoot4fun]

Hi all,

I have some questions about case neck runouts in my 300 PRC load. I did the following tests with 2 fired cases:

1. The OD of my fired necks is 0.3400". Runouts of the case neck is measured at less than 0.0005" here. Great so far.
2. After sizing it with the L.E Wilson die and a 0.335 bushing (0.005" delta) and the RCBS Rock Chucker Supreme, runouts are still less than 0.0005".
3. However, when I size it one more time with a 0.332 bushing (only 0.003" delta), runouts are now measured at 0.002".

Would this amount of runout make a difference on target at, say at 1000 yards?
Is there a reason why runouts occur on the second sizing but not the first?
For those running with high neck tension, do you size the neck once or you do in smaller increments to avoid runouts?

Thanks!

It would seem the only difference in what you do with the .332 bushing v. the .335 bushing is the actual bushing itself.
So, maybe something about that .335 bushing is the cause of the additional runout?
Have you tried one skipping the .332 stage of the neck sizing and going straight to the .335 bushing to see if the same occurs?
EDIT:
Actual runout is half the reading so .002 is a very acceptable number in my opinion.

 

[Straightshooter1]

Hi all,

I have some questions about case neck runouts in my 300 PRC load. I did the following tests with 2 fired cases:

1. The OD of my fired necks is 0.3400". Runouts of the case neck is measured at less than 0.0005" here. Great so far.
2. After sizing it with the L.E Wilson die and a 0.335 bushing (0.005" delta) and the RCBS Rock Chucker Supreme, runouts are still less than 0.0005".
3. However, when I size it one more time with a 0.332 bushing (only 0.003" delta), runouts are now measured at 0.002".

Would this amount of runout make a difference on target at, say at 1000 yards?
Is there a reason why runouts occur on the second sizing but not the first?
For those running with high neck tension, do you size the neck once or you do in smaller increments to avoid runouts?

Thanks!

In my limited experience and trying various bushing dies (quality ones at that), I found it typical to get TIR's of .002 or greater. . . mostly greater. .002" isn't really all that bad and not likely going to have an effect at 1000" yds. depending on your gun and what you're trying to accomplish at 1000 yds. It could potentially result in greater bullet seating TIR, but that's depends on what your seating die is capable of.

Being the perfectionist I am, I don't use my bushing dies and stick to non-bushing sizing dies and run expander mandrels to get the neck tension I'm after. I like that my neck's TIR's run .0005 or less and my bullet TIR's are run <.001 (though occasionally I will get a cartridge with a TIR .001-.002) and at .002 TIR, I don't see any difference at distance.

BTW: the thing that's helped my most, even with non-bushing sizing dies, is having the die made so that the neck is only minimally sized down so the expander ball doesn't have to do much work. Also, annealing after every firing helps with that.

 

[JayHHI6818]

Could be bushing

Uniformity of Die Neck Bushings — Run-out Revealed « Daily Bulletin

Do you use bushings to size your case-necks? Are you assuming that your bushings are actually round on the inside, with a hole that's centered-up properly? Well you may be in for an unpleasant surprise, based on what our friend Jim de Kort recently discovered. Jim was concerned about the run-out...

bulletin.accurateshooter.com

 

[markd657]

It would seem the only difference in what you do with the .332 bushing v. the .335 bushing is the actual bushing itself.
So, maybe something about that .335 bushing is the cause of the additional runout?
Have you tried one skipping the .332 stage of the neck sizing and going straight to the .335 bushing to see if the same occurs?
EDIT:
Actual runout is half the reading so .002 is a very acceptable number in my opinion.

I suspect it could be the bushing. the problem is the issue occurs with the 0.332 bushing and I have to use the 0.335 die first.

 

[markd657]

In my limited experience and trying various bushing dies (quality ones at that), I found it typical to get TIR's of .002 or greater. . . mostly greater. .002" isn't really all that bad and not likely going to have an effect at 1000" yds. depending on your gun and what you're trying to accomplish at 1000 yds. It could potentially result in greater bullet seating TIR, but that's depends on what your seating die is capable of.

Being the perfectionist I am, I don't use my bushing dies and stick to non-bushing sizing dies and run expander mandrels to get the neck tension I'm after. I like that my neck's TIR's run .0005 or less and my bullet TIR's are run <.001 (though occasionally I will get a cartridge with a TIR .001-.002) and at .002 TIR, I don't see any difference at distance.

BTW: the thing that's helped my most, even with non-bushing sizing dies, is having the die made so that the neck is only minimally sized down so the expander ball doesn't have to do much work. Also, annealing after every firing helps with that.

what I'm trying to accomplish is silly but it's getting 0.5MOA group at 1000 yards with a factory rifle. just for fun not competition.

rookie question: so you believe using a non-bushing die and an expander is more precise than using a neck bushing?

 

[markd657]

What kind of dies are you using? are you using new brass/unfired before turning them?

L.E. Wilson die and bushings. These are 1x fired cases.

 

[Webster]

Hi all,

I have some questions about case neck runouts in my 300 PRC load. I did the following tests with 2 fired cases:

1. The OD of my fired necks is 0.3400". Runouts of the case neck is measured at less than 0.0005" here. Great so far.
2. After sizing it with the L.E Wilson die and a 0.335 bushing (0.005" delta) and the RCBS Rock Chucker Supreme, runouts are still less than 0.0005".
3. However, when I size it one more time with a 0.332 bushing (only 0.003" delta), runouts are now measured at 0.002".

Would this amount of runout make a difference on target at, say at 1000 yards?
Is there a reason why runouts occur on the second sizing but not the first?
For those running with high neck tension, do you size the neck once or you do in smaller increments to avoid runouts?

Thanks!

Just looked at several runout gauges. Looks to me like the case body o.d. is a terrible reference standard to compare bullet runout to. The body is used because there is no other way to do it.

 

[Straightshooter1]

what I'm trying to accomplish is silly but it's getting 0.5MOA group at 1000 yards with a factory rifle. just for fun not competition.

rookie question: so you believe using a non-bushing die and an expander is more precise than using a neck bushing?

I'm in the same boat in that my rifle is a "factory" gun is just for fun , though I no longer have a factory barrel on it nor the factory trigger (a trigger just slightly better than factory) and I manage to get a little better than .5 MOA. I'm pretty pleased with that considering when I bought the gun it seemed like everyone was saying I was wasting my time and it wasn't possible to get that kind of precision from it.

Going by the facts of my experience (and some from others as well) where I tried various bushing dies and tried everything I could to get them to work well. I could not get them to work as well an my non-bushing dies with an expander mandrel to follow. The bushings are supposed to be self aligning, but they just don't align well enough (for me) and I experimented extensively with how the bushing fit, including rotating the die or case as well as how fast the case was inserted into the die. Interestingly to me, a very fast entry would give me the best result. So, yes. . . that's my "belief" based on all the hours of my work trying to match the results I get with a non-bushing die.

BTW: While I got pretty consistent results from my Sinclair Expander Die, I had to try Cortina's new expander die. Because his die is somewhat tight to the web area of the case (it's caliber specific), it seems to hold the case producing even more consistent results.

 

[ShtrRdy]

Did you try turning the 0.332 bushing over to see if it will still be 0.002" runout?

 

[LCazador]

So you go from .340" to .335" not good to size down that much but congrats. I'd assume that you have a defective bushing so you may want to try a different bushing in the same size. Brass fired one time in your chamber or bought that way? Whats you instrument for measuring?

 

[Straightshooter1]

Did you try turning the 0.332 bushing over to see if it will still be 0.002" runout?

Yup, I did that too. . . even where the bushings were not designed to be used that way.

 

[markd657]

I'm in the same boat in that my rifle is a "factory" gun is just for fun , though I no longer have a factory barrel on it nor the factory trigger (a trigger just slightly better than factory) and I manage to get a little better than .5 MOA. I'm pretty pleased with that considering when I bought the gun it seemed like everyone was saying I was wasting my time and it wasn't possible to get that kind of precision from it.

Going by the facts of my experience (and some from others as well) where I tried various bushing dies and tried everything I could to get them to work well. I could not get them to work as well an my non-bushing dies with an expander mandrel to follow. The bushings are supposed to be self aligning, but they just don't align well enough (for me) and I experimented extensively with how the bushing fit, including rotating the die or case as well as how fast the case was inserted into the die. Interestingly to me, a very fast entry would give me the best result. So, yes. . . that's my "belief" based on all the hours of my work trying to match the results I get with a non-bushing die.

BTW: While I got pretty consistent results from my Sinclair Expander Die, I had to try Cortina's new expander die. Because his die is somewhat tight to the web area of the case (it's caliber specific), it seems to hold the case producing even more consistent results.

thanks. I might try the expander route if nothing works.
curious, what type of rifle and what caliber?

 

[markd657]

Did you try turning the 0.332 bushing over to see if it will still be 0.002" runout?

good idea! I'll try tonight.

 

[Straightshooter1]

thanks. I might try the expander route if nothing works.
curious, what type of rifle and what caliber?

.308 and 6.5 PRC . . . both are RPR's The .308 is pictured in my avatar.

 

[markd657]

So you go from .340" to .335" not good to size down that much but congrats. I'd assume that you have a defective bushing so you may want to try a different bushing in the same size. Brass fired one time in your chamber or bought that way? Whats you instrument for measuring?

Brass was fired twice.

I'm using the Sinclair Concentricity Gauge.

Can you help me understand, Is it not good because of brass' life concerns or is it because sizing down that much causes runouts? Or is it something else?

The chamber is SAAMI spec (as I was told by the gunsmith) and this is Lapua brass with 0.015" neck thickness. If after firing, OD is 0.3400" then ID is 0.3100". If someone wants to try a higher neck tension in these factory rifles, say 0.004", they would have to get the ID down to at least 0.304. That will require sizing the OD down by 0.006". So I deduce from what you said, it's more ideal to use high neck tension in a neck-turn chamber?

 

[Straightshooter1]

Brass was fired twice.

I'm using the Sinclair Concentricity Gauge.

Can you help me understand, Is it not good because of brass' life concerns or is it because sizing down that much causes runouts? Or is it something else?

The chamber is SAAMI spec (as I was told by the gunsmith) and this is Lapua brass with 0.015" neck thickness. If after firing, OD is 0.3400" then ID is 0.3100". If someone wants to try a higher neck tension in these factory rifles, say 0.004", they would have to get the ID down to at least 0.304. That will require sizing the OD down by 0.006". So I deduce from what you said, it's more ideal to use high neck tension in a neck-turn chamber?

Yes, sizing down a lot, like typical FL sizing dies do, does tend to induce more runout (including more springback and work hardening on the brass). This is why I have my non-bushing FL sizing dies reamed. . . like my .308 die size the necks to an OD of .332. I should point out here too that I turn all my brass and my .308 brass is turned to .014" thick, mostly to remove any thickness variances. To get my .002 neck tension the expander mandrel expands my necks to .334 (ID = .306). So the expander mandrel isn't doing a lot of work on the neck going from .332 to .334, which really helps in keeping the TIR low. The same principle works with bushing dies + expander mandrel, but not quite as good according to my personal experience.

 

[Mark611]

JMO and my experience, I don't know what brass you are using? but I would start there, secondly, I don't use bushing dies, my best results come from a simple Redding body die and a LEE collet die! When I get new brass LAPUA or ALFA, I check all the case through a Sheridan slotted case gage, if they fit the gage which they usually do, I use a Sinclair carbide expander mandrel, and make sure the necks are sized to that mandrel, I then set up my neck turning tool with the carbide neck turning mandrel, I will then measure the neck wall thickness, I will find the low spot in the neck wall, that's after checking several cases to find an average thickness, I set the cutter to just touch the low spot in the neck, then adjust the depth or length of the cut so I stop just at the shoulder of the neck, then turn a piece and check it, if all is well, this usually removes 1k of material of the neck, just to basically uniform the necks, after that I run them through the LEE collet die, my necks are usually less the 1k with the runout! I then check all the flash holes and uniform them as well along with chamfer and deburring the case mouth, this is how I do it and have done it for years, I use this process for every cartridge I want the best chance for accuracy, theirs more than 1 way to skin a cat, this is how I do it! also, I would fire your cases at least 3x if possible before you resize them other than the neck sizing, and anneal them every time you fire them before sizing, YMMV

 

[LCazador]

Brass was fired twice.

I'm using the Sinclair Concentricity Gauge.

Can you help me understand, Is it not good because of brass' life concerns or is it because sizing down that much causes runouts? Or is it something else?

The chamber is SAAMI spec (as I was told by the gunsmith) and this is Lapua brass with 0.015" neck thickness. If after firing, OD is 0.3400" then ID is 0.3100". If someone wants to try a higher neck tension in these factory rifles, say 0.004", they would have to get the ID down to at least 0.304. That will require sizing the OD down by 0.006". So I deduce from what you said, it's more ideal to use high neck tension in a neck-turn chamber?

Best way to figure bullet tension is use the loaded neck diameter. In your case that would be bullet diameter plus .015 neck thickness = .338" loaded diameter. Using a .335" bushing should give .003" neck tension and using a .334" bushing should give .004" neck tension. That fired neck OD dimension of .3400 would be one or two thousands under your chamber diameter if you add brass springback of .001"-.002". So assuming your measurement is correct on the fired brass you have a neck clearance of .004" on your loaded cartridge. That sounds like a custom chamber? Is this a custom or factory?