Neck tension via mandrel

[Slim13]

Getting ready to reload for a 6.5 Saum. With my other rifles, I used custom honed Forster FL sizing does with their expander ball. It produces epic results. I spoke with the fine folks at Forster and they can’t help me with a 6.5 Saum. It sounds like most folks that are running them are going with the Redding Type S FL bushing dies (or Whidden). I’ve got a .263 expander mandrel. Would it make sense to run a Mandrel through the necks after FL sizing (without using an expander ball) in order to set neck tension? I figure a .263 mandrel should provide .0015-.002 factoring in spring back. I do like the notion of pushing case neck imperfections to the outside of the neck.

Sorry if that’s long winded and maybe I’m making it more complicated than it needs to be. I’ve been spoiled by sending in fired brass and a loaded round measurements to Forster, and getting a die that matches perfectly. This time around, I need to learn a new way. Thanks.

 

[David Christian]

Go with the bushing die and remove the expander ball. You can create your own custom neck tension set up by ordering yourself a set of individual gage pins .2620, .2625, .2630, .2635. .2640 from here:
https://www.gageshop.com/product/english-class-z-gage-pins-011-to-0605/
Round over/taper one end of each pin so that they slide into your cases with ease.

You will also need this type of bullet puller to hold the pins.

Yes, post FL sizing you are ready to test any neck tension you desire as well as can measure the real spring back of your cases. Good luck!

 

[243winxb]

. I’ve been spoiled by sending in fired brass and a loaded round measurements to Forster, and getting a die that matches perfectly.

Redding makes custom dies from 3 of your fired brass. Get a price quote first.

 

[Hydenseek]

Good strategy if your necks are turned.

 

[jepp2]

and they can’t help me with a 6.5 Saum

Or you could hone your own die to the diameter you want.

 

[Ccrider]

Go with the bushing die and remove the expander ball. You can create your own custom neck tension set up by ordering yourself a set of individual gage pins .2620, .2625, .2630, .2635. .2640 from here:
https://www.gageshop.com/product/english-class-z-gage-pins-011-to-0605/
Round over/taper one end of each pin so that they slide into your cases with ease.

You will also need this type of bullet puller to hold the pins.
View attachment 1085966
Yes, post FL sizing you are ready to test any neck tension you desire as well as can measure the real spring back of your cases. Good luck!

Tried the link. Did not see where you have the options for 2620, 2625, etc. Do you have to special order?

 

[jds holler]

I like the idea of my final neck dimension being created by an inside mandrill. It just makes sense to me - especially in the instance where neck thickness may vary a bit. jd

 

[mikecr]

You can create your own custom neck tension set up by ordering yourself a set of individual gage pins .2620, .2625, .2630, .2635. .2640

I'm compelled to attempt explaining neck tension again, another way.
Neck tension IS NOT interference fit, and it IS NOT seating/pull force. Neck tension is spring back force gripping an area of seated bullet bearing (force * area).

In 26cal, necks spring back ~1thou max. The force of this holds bullets.
So with 1thou interference fit against your full seated bearing area, you have max controllable tension. Interference beyond seated bearing is what I consider uncontrolled (undesired) tension in that it causes binding forces with a great deal of variance.

If you downsize/expand 26cal necks to say .2600 ID, you do not have 4thou of tension gripping .2640 diameter bullets. Taking them to .2620 ID, does not give you 2thou of tension. You only get 1thou of spring back force -max.
Go ahead and try it. Cause neck IDs below .2630,, any amount you want. Then seat a bullet into that interference, and then pull the bullet. Now measure neck ID, and you'll find it springing back to no less than .2630. That's what you get, and any more interference was merely expanded by the seated bullet.
Keep in mind that bullets are not for neck upsizing. That's what hardened expanders are for.

To adjust tension go back to force * area. Adjust the area of max spring back force (~1thou) gripping your seated bullet bearing.
Expansion in itself is worthy to do because it establishes spring back in an inward direction(increasing tension), instead of outward (decreasing tension). This is important for ammo that will not be used right away.
Mandrels are good for driving thickness variance outward, allowing for straighter ammo. Keep in mind that to change/move/size brass, any direction/dimension, means causing that brass to yield.
Ideally 26cal necks would be downsized to ~.262 (after outward spring back), by a load developed sizing length, then expanded with a .264 mandrel, where they would spring back to ~.263 (after inward spring back), ready for bullet seating -that is not upsizing necks.

 

[47WillysGuy]

Getting ready to reload for a 6.5 Saum. With my other rifles, I used custom honed Forster FL sizing does with their expander ball. It produces epic results. I spoke with the fine folks at Forster and they can’t help me with a 6.5 Saum. It sounds like most folks that are running them are going with the Redding Type S FL bushing dies (or Whidden). I’ve got a .263 expander mandrel. Would it make sense to run a Mandrel through the necks after FL sizing (without using an expander ball) in order to set neck tension? I figure a .263 mandrel should provide .0015-.002 factoring in spring back. I do like the notion of pushing case neck imperfections to the outside of the neck.

Sorry if that’s long winded and maybe I’m making it more complicated than it needs to be. I’ve been spoiled by sending in fired brass and a loaded round measurements to Forster, and getting a die that matches perfectly. This time around, I need to learn a new way. Thanks.

I size with a body die, then squeeze the necks with a Lee Collett Die, and lastly run a 0.263 expander into the necks. I perfer a light neck tension. Runout average is 0.0015”.

 

[David Christian]

Tried the link. Did not see where you have the options for 2620, 2625, etc. Do you have to special order?

@Ccrider, here is the link to the next group of pins.
https://www.gageshop.com/product/english-class-z-gage-pins-061-to-5005/

 

[Ccrider]

@Ccrider, here is the link to the next group of pins.
https://www.gageshop.com/product/english-class-z-gage-pins-061-to-5005/

Thanks. Looking for .243

 

[Ccrider]

All said and done, if I want .002 neck tension on my .243 bullet I need to expand back up to .240, and presumably, spring back will be around .241?

 

[Dusty Stevens]

I'm compelled to attempt explaining neck tension again, another way.
Neck tension IS NOT interference fit, and it IS NOT seating/pull force. Neck tension is spring back force gripping an area of seated bullet bearing (force * area).

In 26cal, necks spring back ~1thou max. The force of this holds bullets.
So with 1thou interference fit against your full seated bearing area, you have max controllable tension. Interference beyond seated bearing is what I consider uncontrolled (undesired) tension in that it causes binding forces with a great deal of variance.

If you downsize/expand 26cal necks to say .2600 ID, you do not have 4thou of tension gripping .2640 diameter bullets. Taking them to .2620 ID, does not give you 2thou of tension. You only get 1thou of spring back force -max.
Go ahead and try it. Cause neck IDs below .2630,, any amount you want. Then seat a bullet into that interference, and then pull the bullet. Now measure neck ID, and you'll find it springing back to no less than .2630. That's what you get, and any more interference was merely expanded by the seated bullet.
Keep in mind that bullets are not for neck upsizing. That's what hardened expanders are for.

To adjust tension go back to force * area. Adjust the area of max spring back force (~1thou) gripping your seated bullet bearing.
Expansion in itself is worthy to do because it establishes spring back in an inward direction(increasing tension), instead of outward (decreasing tension). This is important for ammo that will not be used right away.
Mandrels are good for driving thickness variance outward, allowing for straighter ammo. Keep in mind that to change/move/size brass, any direction/dimension, means causing that brass to yield.
Ideally 26cal necks would be downsized to ~.262 (after outward spring back), by a load developed sizing length, then expanded with a .264 mandrel, where they would spring back to ~.263 (after inward spring back), ready for bullet seating -that is not upsizing necks.

Heres where the calculator and target disagree. Anybody thats ever done neck tension testing can see the difference between .001 and .002 and especially .003 interference fit

 

[Martin52]

......

To adjust tension go back to force * area. Adjust the area of max spring back force (~1thou) gripping your seated bullet bearing.

As an aside, this supports/validates measuring projectile BTO ? Assuming all projectiles are seated the same and the boat tail is above the neck shoulder junction, then the variable is the amount of bearing surface that is in contact with the inside of the neck - and this will vary if the projectiles have varying BTO measurements...? Tension will vary because 'force * area' will produce different tension as a result of the variation in area....I am thinking out loud here.

 

[AlNyhus]

....and maybe I’m making it more complicated than it needs to be. Thanks.

Get a Redding or Whidden f.l. bushing die and bushings that measure .002, .003 and .004 under what the neck of a loaded round measures. Forget about expanders or mandrels.

It's that simple..... -Al

 

[ngb1787]

The most important thing in reloading to me with everything else being equal is neck tension.

 

[AlNyhus]

The most important thing in reloading to me with everything else being equal is neck tension.

Yes...and it's amazing how few people ever test neck tension. They buy into the urban myths (perpetuated by those that have never tested neck tension ) and just blam, blam away.

All the while, better accuracy may be only a $15 bushing away. -Al

 

[mikecr]

All said and done, if I want .002 neck tension on my .243 bullet I need to expand back up to .240, and presumably, spring back will be around .241?

No, if you EXPAND to .240 the neck would spring back opposite this sizing to ~.239.
And no matter what you do, you WILL NEVER have .002 of neck tension. All you can get is .002 of interference, which is removed by bullet seating.

Look folks, you can set neck dimension with a bushing, and/or expander, and/or with bullets, but the outcome is the same. With a bullet seated the neck ID goes to cal, and neck OD goes to cal + neck thickness. Right? And no matter what you do or think you're doing, this is the outcome.
If you pull a seated bullet from this condition the neck will only spring back ~1thou. It will not spring back to whatever interference you had set that's greater than this ~1thou.
This is because your bullet is expanding any interference greater than ~1thou, just as an expander would. So whether you expand necks with an expander, or bullet, it's the same action and same result.
Bullets are not gripped by 'intent', but by a spring back force (a hoop tension), which we currently have no way to measure.

As mentioned earlier, you could increase the gripping force beyond this, by causing interference beyond seated bullet bearing. This would leave a binding force on bearing-base junction from the non-upsized portion of the neck. That is, the portion that the bullet was not seated deep enough to upsize.
FL sizing of necks does this, and it brings donut area into this binding.
I'll concede that in this situation, 2 or 3thou of interference leads to more gripping force than 1thou of interference. But there is no way I would ever do that or rely on that, unless shooting an underbore that actually prefers it. A cartridge that viably likes extreme starting pressures, regardless of it's variance, like 6PPC, 30br,, maybe 6.5x47L.

A good thing about bushing dies, that nobody merchandises on,, is that you can adjust neck sizing length as well as diameter.
If you desire truly consistent neck tension, you'll partial size necks, no longer than seated bearing. And you can reliably adjust tension here through adjustment of that sizing length.
That bullet bearing itself may vary makes no difference provided your sizing length never goes beyond seated bearing, and never beyond the sizing length YOU set. Also, seated bearing should not ever be allowed to contact donuts (which vary), or neck-shoulder junction (which expands different than necks).

 

[Fliers]

Why do people say they need .002 or .003 to avoid pushback in semi-auto guns?

 

[JMayo]

No, if you EXPAND to .240 the neck would spring back opposite this sizing to ~.239.
And no matter what you do, you WILL NEVER have .002 of neck tension. All you can get is .002 of interference, which is removed by bullet seating.

Look folks, you can set neck dimension with a bushing, and/or expander, and/or with bullets, but the outcome is the same. With a bullet seated the neck ID goes to cal, and neck OD goes to cal + neck thickness. Right? And no matter what you do or think you're doing, this is the outcome.
If you pull a seated bullet from this condition the neck will only spring back ~1thou. It will not spring back to whatever interference you had set that's greater than this ~1thou.
This is because your bullet is expanding any interference greater than ~1thou, just as an expander would. So whether you expand necks with an expander, or bullet, it's the same action and same result.
Bullets are not gripped by 'intent', but by a spring back force (a hoop tension), which we currently have no way to measure.

As mentioned earlier, you could increase the gripping force beyond this, by causing interference beyond seated bullet bearing. This would leave a binding force on bearing-base junction from the non-upsized portion of the neck. That is, the portion that the bullet was not seated deep enough to upsize.
FL sizing of necks does this, and it brings donut area into this binding.
I'll concede that in this situation, 2 or 3thou of interference leads to more gripping force than 1thou of interference. But there is no way I would ever do that or rely on that, unless shooting an underbore that actually prefers it. A cartridge that viably likes extreme starting pressures, regardless of it's variance, like 6PPC, 30br,, maybe 6.5x47L.

A good thing about bushing dies, that nobody merchandises on,, is that you can adjust neck sizing length as well as diameter.
If you desire truly consistent neck tension, you'll partial size necks, no longer than seated bearing. And you can reliably adjust tension here through adjustment of that sizing length.
That bullet bearing itself may vary makes no difference provided your sizing length never goes beyond seated bearing, and never beyond the sizing length YOU set. Also, seated bearing should not ever be allowed to contact donuts (which vary), or neck-shoulder junction (which expands different than necks).

I'm really interested in this topic.
I load a 6mm bra. I don't use a mandrel. I do use a 262 neck bushing (something like that, I forget the exact#). I have one smaller and one bigger to experiment when load testing.
I pay attention to seating force. Wanting the same force on all competition rounds.
What am I missing here in your opinion?