Case neck has 0.002" runout after neck sizings

[markd657]

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?

The rifle is an off-the-shelf rifle (AI AXSR) but I have since replaced the factory barrel with this one. It was purchased from a gun-smith that makes pre-fit barrels for this rifle and I did not give him any specifications to follow.
I assume he made the chamber exactly the same as the factory rifle. Sorry if that wasn't the case. I did not mean to mislead. Would a factory chamber have bigger neck clearance?

 

[LCazador]

The rifle is an off-the-shelf rifle (AI AXSR) but I have since replaced the factory barrel with this one. It was purchased from a gun-smith that makes pre-fit barrels for this rifle and I did not give him any specifications to follow.
I assume he made the chamber exactly the same as the factory rifle. Sorry if that wasn't the case. I did not mean to mislead. Would a factory chamber have bigger neck clearance?

So that may explain why you may have a tight chamber. Yes the factory SAMMI chamber would have different dimensions. It might behoove you to ask the gunsmith for a blue print with dimensions of the chamber.

 

[LCazador]

The rifle is an off-the-shelf rifle (AI AXSR) but I have since replaced the factory barrel with this one. It was purchased from a gun-smith that makes pre-fit barrels for this rifle and I did not give him any specifications to follow.
I assume he made the chamber exactly the same as the factory rifle. Sorry if that wasn't the case. I did not mean to mislead. Would a factory chamber have bigger neck clearance?

It's not sorry on your part, BTW , but sorry on your gunsmith's part not to inform you of any difference in chamber dimensions but things do happen. I certainly don't think he meant to leave anything out intentionally , maybe some assumptions on both parts. Trying to help not point fingers.

 

[markd657]

So that may explain why you may have a tight chamber. Yes the factory SAMMI chamber would have different dimensions. It might behoove you to ask the gunsmith for a blue print with dimensions of the chamber.

Checking the invoice that came with the barrel, I see:

Neck diameter 0.342"
Freebore 0.233"

 

[Fast14riot]

If neck sizing, try a Lee collet neck die. They produce extremely straight brass and are not affected by brass wall thickness. Need more neck tension just chuck the mandrel in a drill and polish it down to your desired diameter. I actually load my competition brass with a ring die (as needed), body die and CND and have done so for years. Still shooting HM scores with it.

 

[LCazador]

Checking the invoice that came with the barrel, I see:

Neck diameter 0.342"
Freebore 0.233"

So it is a custom chamber and the best way to deal with this is to use a bushing die with the proper bushing
diameter. Use the blind expander for the decapping rod so you size the neck to desired neck tension. In this case as I indicated a .335" bushing or .334" bushing. May I add this would be a full length type S bushing die. Also since you have a custom chamber you may want to set your sizing die bump with a competition shell holder set. A great investment in my opinion.

 

[L.Sherm]

If your getting .5 moa out of a hunting rifle at 1,000 yards i would just put the runout guage on the shelf and forget about it.
The only thing I might change is your neck- chamber clearance, on bigger calibers I like .005 min.

 

[rlporter507]

could it be that the brass is springing back unevenly to induce measured runout? I have been fighting this same problem for awhile, and the SAC bushings solved my problem, but then my neck tension changed measured with a pin gauge on the inside, so i had to change bushing size, and my loads did not shoot as well. Still working on the problem.

 

[Webster]

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

The bushings have a very slight chamfer on one side so the neck enters the bushing without banging against the wall.

 

[markd657]

If your getting .5 moa out of a hunting rifle at 1,000 yards i would just put the runout guage on the shelf and forget about it.
The only thing I might change is your neck- chamber clearance, on bigger calibers I like .005 min.

I am not at the 0.5MOA at 1K level yet! hopefully soon.

 

[markd657]

could it be that the brass is springing back unevenly to induce measured runout?

I would expect 0.0005" or 0.001" spring-back but not this much!

I have been fighting this same problem for awhile, and the SAC bushings solved my problem, but then my neck tension changed measured with a pin gauge on the inside,

did it get 0.001" larger?

 

[L.Sherm]

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.

This is what I was referring too.

 

[rlporter507]

yes, almost, I also started annealing at the same time as the bushing change, so i went down .002 on the bushing to get the same inside dia. Im pretty sure there was .001 of carbon on the inside, and when this got burned off that was most of my .002 on the bushing.
the sac bushings were the same runout as the unturned brass, at or less than .001.
before with the redding bushing, i was .001 to .003 runout.
I have since stopped annealing, and went back to the redding bushing to get back where i was in accuracy. not positive that is my problem, had to change powder lots in there also. so when the weather warms again, another lot of powder and new brass starting over. I will try just the sac bushing on a box and see what it does.