New to mandrel expanders have questions

Mike from Texas

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I used the search function and read until my eyes crossed but didn’t see a couple of specific questions I have.

I’ve never used expansion mandrels. I’ve always used bushing dies. I can see the logic behind inside expanders vs outside so I want to give it a try to compare.
  • I’ve looked at Sinclair & 21st century so far. I’ve seen a couple of others mentioned but haven’t looked into them yet. Is there one brand that is better than others?
  • What about carbide vs regular steel? If the carbide worth 3x the price?
  • If carbide is not worth the extra cost what lube is recommended with the steel ones? I normally use Imperial wax but what about the dry graphite lube? Would it be sufficient?
  • All of my dies that I currently own for my rifle calibers are currently Redding type S bushing dies. Should I size with the outside bushing and then inside size with the mandrel?
  • Is there a preferred size under Bullet diameter? I see the Sinclair carbide does only provide .001 under but some of the steel ones provide up to .003 under. If it matters many of these will be hunting rifles so is .001 under a sufficient amount of neck tension for a repeater rifle?
 

Savage 12BVSS

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  • I’ve looked at Sinclair & 21st century so far. I’ve seen a couple of others mentioned but haven’t looked into them yet. Is there one brand that is better than others?
  • What about carbide vs regular steel? If the carbide worth 3x the price?
  • If carbide is not worth the extra cost what lube is recommended with the steel ones? I normally use Imperial wax but what about the dry graphite lube? Would it be sufficient?
  • All of my dies that I currently own for my rifle calibers are currently Redding type S bushing dies. Should I size with the outside bushing and then inside size with the mandrel?
  • Is there a preferred size under Bullet diameter? I see the Sinclair carbide does only provide .001 under but some of the steel ones provide up to .003 under. If it matters many of these will be hunting rifles so is .001 under a sufficient amount of neck tension for a repeater rifle?
Sinclair would be my choice but 21st is also comparable quality, I own the sinclairs and they are excellent.

Carbide will last longest and work better without lube, the coated are the mid priced and coating will wear off slowly. Steel are cheapest but will slide hardest without lube and scratch the brass sometimes.

Try the steel first and see what you think of them, replace with carbide if you like em. Lot of loader's like to not use lube inside the necks, like to case neck brush em' and go. Dry graphite would be best if you use something. I use nothing myself.

You have to size with something, I use sizing dies with the expander button's removed.

I would suggest you look at lee collet/mandrel neck dies with no lube. Amazing concentricity and do it all in one step. Hope I helped Dave
 

Mikecr

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Be careful with assumptions about a collet approach.
The object here is to get bullets pointed straight.
Outside action only will leave thickness variance in necks in interference with straight seating.
The purpose of expanding mandrel use is not to set tension, but to drive that variance outward -away from seating bullets, for straighter overall ammo.

A basic thing also that every reloader needs to understand is that neck tension is not whatever interference you set.
Neck tension is spring back gripping of bullets. And necks spring back less than 1thou, so any interference beyond this is not contributing to tension, as bullet seating is merely expanding/undoing that excess.

Either downsizing(with a bushing) or upsizing (with a mandrel), or in fact any sizing, means brass is taken to yield, and does not fully spring back to pre-sizing dimension.
Sizing adds energy to brass, and that brass will try to get back to lowest energy level. Much of this happens with initial spring back, but that spring back also continues over time (if it can).
If you last sizing action with necks is down sizing, those necks will spring back outward initially, and they will continue to spring back outward over time. This, reducing neck tension over time.
Neck expansion in general should be done to ensure that there will always be sufficient tension.
This expansion is best done with a mandrel rather than bullets (which are terrible expanders).
I call mandrel expansion 'pre-seating'.

If your mandrel is 1thou under cal, this is what you can successfully do:
Set your bushing ~3thou under loaded neck OD. After downsizing with this, the neck will spring back outward a bit under 1thou to maybe ~2.25thou under cal. Then the expander mandrel will size up from here and the neck will spring back inward a bit under 1thou from that to ~1.25thou under cal. That in itself is excess but not by much. It'll work just fine.
These numbers are variables subject to trial & error because the bushing results vary with sizing amount (angular variances).

Last thing: NEVER FL size necks.
Another tread to explain that, but just don't...
 

Mike from Texas

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Joined
Sep 7, 2013
Messages
134
Location
North Texas
Be careful with assumptions about a collet approach.
The object here is to get bullets pointed straight.
Outside action only will leave thickness variance in necks in interference with straight seating.
The purpose of expanding mandrel use is not to set tension, but to drive that variance outward -away from seating bullets, for straighter overall ammo.

A basic thing also that every reloader needs to understand is that neck tension is not whatever interference you set.
Neck tension is spring back gripping of bullets. And necks spring back less than 1thou, so any interference beyond this is not contributing to tension, as bullet seating is merely expanding/undoing that excess.

Either downsizing(with a bushing) or upsizing (with a mandrel), or in fact any sizing, means brass is taken to yield, and does not fully spring back to pre-sizing dimension.
Sizing adds energy to brass, and that brass will try to get back to lowest energy level. Much of this happens with initial spring back, but that spring back also continues over time (if it can).
If you last sizing action with necks is down sizing, those necks will spring back outward initially, and they will continue to spring back outward over time. This, reducing neck tension over time.
Neck expansion in general should be done to ensure that there will always be sufficient tension.
This expansion is best done with a mandrel rather than bullets (which are terrible expanders).
I call mandrel expansion 'pre-seating'.

If your mandrel is 1thou under cal, this is what you can successfully do:
Set your bushing ~3thou under loaded neck OD. After downsizing with this, the neck will spring back outward a bit under 1thou to maybe ~2.25thou under cal. Then the expander mandrel will size up from here and the neck will spring back inward a bit under 1thou from that to ~1.25thou under cal. That in itself is excess but not by much. It'll work just fine.
These numbers are variables subject to trial & error because the bushing results vary with sizing amount (angular variances).

Last thing: NEVER FL size necks.
Another tread to explain that, but just don't...
Thanks for the very detailed response. Regarding the Lee Collet sizer, it’s my understanding that they produce very low runout since they use a mandrel and the collet to do the neck sizing. It looks like the standard mandrel they use is .002 less that caliber. In my case I’m looking at various 6.5mm cartridges so the mandrel that comes with it is sized at .262. again this is only my observation from what I’ve seen in videos and various forum posts. For around $30 I may give it a try to see for myself. Either way, good or bad, it will just add to my experiences.

Your description of the .003 under sizing with the neck bushing and expanding with the mandrel is the exact plan I had in mind. I typically undersized .003 from loaded outside diameter.

One last though for a repeater rifle fed from either an internal box or detachable mag, do you feel that .001 will provide enough tension on the necks to prevent potential bullet setback?
 

Bill Cauley Jr

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Thanks for the very detailed response. Regarding the Lee Collet sizer, it’s my understanding that they produce very low runout since they use a mandrel and the collet to do the neck sizing. It looks like the standard mandrel they use is .002 less that caliber. In my case I’m looking at various 6.5mm cartridges so the mandrel that comes with it is sized at .262. again this is only my observation from what I’ve seen in videos and various forum posts. For around $30 I may give it a try to see for myself. Either way, good or bad, it will just add to my experiences.

Your description of the .003 under sizing with the neck bushing and expanding with the mandrel is the exact plan I had in mind. I typically undersized .003 from loaded outside diameter.

One last though for a repeater rifle fed from either an internal box or detachable mag, do you feel that .001 will provide enough tension on the necks to prevent potential bullet setback?
If you’re mandrel is undersized by .001you’ll have approximately 1 1/2 thousand’s neck tension remember a bushing squeezes in Word brass Springs outward with a mandrel you’re stretching the brass outward therefore it will spring back in word And yes one and a half thousands tension is a minimum for me i usually use 2 1/2 thousandths I turn necks and therefore I use my turning mandrel which is 2000s under caliber
 

Mikecr

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With necks sized no longer than seated bearing, any interference beyond spring back, which is no way over 1thou, means nothing. This, because the bullet will just size back up on seating.

Try it yourself. Measure neck OD before seating, seat a bullet, measure neck OD again, pull the bullet, measure what neck OD springs back to. It's no more than 1thou smaller than seated OD. That's all you get.
You could size necks down 5thou for what you 'think' is tension. Nope. Does the same thing, and that is in no way what 'tension' is.

With partial sized necks it don't matter to tension if you size down 1thou or 10thou. Here, what matters(how tension is adjusted) is the length of sizing. Spring back force x area applied [PSI].
With necks sized in length beyond seated bearing(like FL sized) it matters, and it sucks completely, because tension goes all over the map. This because that spring back force is then binding to the bullet's base-bearing junction, and you've included donut and shoulder angle to release.
 

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