Neck Tension

[Kmotz23]

So every once in a blue moon a shooter needs to ask a dumb question.

I am fairly new go reloading (used prime for a long time) and am having an issue.
I’m on my 4th firing of Lapua brass ( 6.5 CM 130 OTM Hybrids) and I am having crap neck tension even after sizing. Now I’m not a weak guy. But I should not be able to seat a bullet or pull one, after sizing.

all measurements after sizing are in specifications ( using a .289 bushing). Measurements are as follows .290-.291 neck, and shoulder bump of 1.520.

am I doing something wrong? Is the neck tension an indicator that I amjust work hardening the brass too much?

 

[txguero]

I don't think it should be super hard by the fourth firing, especially since you are using a bushing die. Are you using the expander? And how much tension was that bushing giving you at first?

 

[918v]

Yeah you need a tighter bushing

 

[Sieg]

The bullet diameter should be .264"

What's the case neck wall thickness?

If the neck wall is .013 x 2 = .026 + .264 = .290 or 0 to -.001 neck tension.

 

[Kmotz23]

Bullet Diameter is .264.

expander ball is .263

Inside diameter is .260

case wall is .014

 

[Sieg]

Try sizing without using the expander ball and see what you get?

What do the neck OD's measure after being fired?

 

[Kmotz23]

+ or - .002 of .295 after measuring 15 random fired pieces.

BUT this barrel is only approximately 1500 rounds in. I just now have seen my first sign of throat erosion. My fired shoulder size WAS 1.525 now it’s 1.528

 

[2aBaC̶a̶]

Can you feel the expander pull through on the downstroke?

Try a .288 or .287 bushing, and sometimes you can chuck your expander in a drill and hit it with some sand paper to get it down a thou or two so it doesnt undo what the bushing just did.

Do you anneal?

 

[Kmotz23]

Can you feel the expander pull through on the downstroke?

Try a .288 or .287 bushing, and sometimes you can chuck your expander in a drill and hit it with some sand paper to get it down a thou or two so it doesnt undo what the bushing just did.

Do you anneal?

I do not anneal. And yes I can feel the down stroke.

This was my thoughts on what I should do. I just wanted to check with voices whom knew an abundance more than I before I polish an expanded.

 

[Rocketmandb]

Bullet Diameter is .264.

expander ball is .263

Inside diameter is .260

case wall is .014

Check my math on this - it's late and my brain hurts...

When you size the neck using a .289 bushing, unhardened brass should spring back to about .290 - which with your .014 neck wall would yield an inside diameter of .262, for a neck tension of .002. But then you're using an expander ball, which opens the neck back up by .001" and it probably isn't springing back a full .001" to give you back your .002" neck tension. So with unhardened brass you were likely at less than .002"

As brass hardens, it loses its elasticity, so if your brass has hardened sufficiently, you likely aren't getting the full .001" spring back during the neck size and next to none with the expander ball, leaving you with something around .001" of neck tension.

Recommendations:

- Lose the expander ball. Lapua is very consistent so the ball is all but worthless. You're working the brass an extra amount for no real benefit.

- Anneal your brass to get some elasticity back. I anneal every firing.

 

[Sieg]

Feeling the down stroke, before the bushing has sized the neck?

What about the up stroke when the expander is doing it's job after the neck sizing bushing?

Somethings not adding up.

 

[918v]

Check my math on this - it's late and my brain hurts...

When you size the neck using a .289 bushing, unhardened brass should spring back to about .290 - which with your .014 neck wall would yield an inside diameter of .262, for a neck tension of .002. But then you're using an expander ball, which opens the neck back up by .001" and it probably isn't springing back a full .001" to give you back your .002" neck tension. So with unhardened brass you were likely at less than .002"

As brass hardens, it loses its elasticity, so if your brass has hardened sufficiently, you likely aren't getting the full .001" spring back during the neck size and next to none with the expander ball, leaving you with something around .001" of neck tension.

As brass hardens you are getting more spring back, not less.

 

[gigamortis]

I run .001” to .0015” neck tension and anneal my brass necks and shoulders every firing. I also clean my brass ultrasonically. I use a .263” 21st Century TiN coated expander mandrel to set my final neck ID, and I see maybe a .0005” springback, if any at all. I lube my case necks with a little bit of powdered mica before seating a bullet. My SDs are usually 5 and below and my bullets have adequate tension for field conditions.

 

[Kmotz23]

Feeling the down stroke, before the bushing has sized the neck?

What about the up stroke when the expander is doing it's job after the neck sizing bushing?

Somethings not adding up.

Yes I am feeling that as well. Believe me. It’s not adding up too me too. Only thing I can think of is using a smaller bushing. Expanderball is .264 I think

 

[Kmotz23]

I run .001” to .0015” neck tension and anneal my brass necks and shoulders every firing. I also clean my brass ultrasonically. I use a .263” 21st Century TiN coated expander mandrel to set my final neck ID, and I see maybe a .0005” springback, if any at all. I lube my case necks with a little bit of powdered mica before seating a bullet. My SDs are usually 5 and below and my bullets have adequate tension for field conditions.

SD’s aren’t the issue. Went out this weekend. The aforementioned weak neck tension rounds still shot 4.6 SD’s

 

[FUNCTIONAL]

try dropping the expander ball and play with bushings first. The expander ball will kill most any work the bushing does and since you keep having the issue I'd take that out of the equation first.