Using a expander mandrel after using a FL bushing die
- Thread starter TQB
- Start date
Do you think a bullet doesn’t do the same thing? Do you think those irregularities stay on the inside of the neck when a round hard bullet is seated?
The diameter of the neck isn't the only parameter of interest. The springiness of the neck is also important. I also use an FL bushing die and then finish with an expander mandrel. I believe this gives a more consistent true neck tension. One indication of consistent neck tension is that when I adopted the practice of finishing with a mandrel, I noticed more consistent resistance when seating the bullet.
In my opinion is not about irregularities (but some folks will argue for that too), it’s that the ID might be .240 on one case and .241 on another. If you seat a bullet into those, the brass will have different tension on the bullet - despite the fact the bullet expands both ID to .243 (nominal).
Rick300
Gold $$ Contributor
What he said
Yes, but you would like to minimize the bullet functioning as an espender mandrel.
NZ_Fclass
Silver $$ Contributor
The idea of brass prep and correct dimension, is to have the case ready to receive the projectle. I want that bullet in straight!
I've been using an expander mandrel (a neck turning expander since that's all I had at the time) since early 2017 when I first started shooting... I just figured back then, that the bullet only touches the inside portion of the neck - so I wanted the inside of the neck as perfectly round as possible...
Use a bushing die to just bring it just under expander mandrel size, then use the expander mandrel to bring the ID to proper size. Select the bushing to work the brass the least so it will last more reloads. Don't use a bullet for a expander mandrel. Makes a difference. HB
Sandstorm
Gold $$ Contributor
Yup...this.
The guys who use a mandrel, what discipline do you shoot? I don't see the benefit using a mandrel in short range benchrest competition. You would need a separate dedicated press to save time.
High power volume ammo. The 21st Century die/mandrels are in station 1 on both 650s. These are strictly for loading. I don't process brass, I send them out, they come back primed ready to load
Edit. All my mandrels, expanding and turning, are melonited. Next best thing to the expensive carbide offerings.
Last edited:
Below from the Redding bushing die FAQ, if the neck thickness varies .002 or more a smaller bushing should be used and the dies expander should be used. Or an expander mandril die to set the final inside neck diameter.
https://www.redding-reloading.com/tech-line-a-tips-faqs/140-bushing-selection
https://www.redding-reloading.com/tech-line-a-tips-faqs/140-bushing-selection
Tech Line & Tips (FAQs)
Bushing Selection
The above methods of determining bushing size require that the cases being sized have a fairly uniform neck wall thickness or have been neck turned. If the neck wall thickness varies more than 0.002", it may be necessary to use a bushing a couple of thousandths smaller than your calculations indicate, and then use a size button in the die to determine the final inside neck diameter.I would probably use a non bushing die and mandrel before I would us a bushing die and no mandrel 
D-4297
Gold $$ Contributor
I would say that the majority of the shooters who use a expander mandrel are shooting F class , from my experience . We load our rounds and prep our brass based on a "system" / procedure we have learned that has become repeatable and consistent . Our rounds are loaded at home ; before matches , due to the number of rounds we will shoot in a Match . Sometimes as many as 2 - 300 rounds for one big Match . I had 430 rounds loaded for the FCNC this last year , in advance of the Match . Most F shooters strive to reduce their SD/ ES down as low as possible because they've found low SD/ES numbers translate to consistency on the target , generally speaking . As someone already said ; reducing the I.D. to a dimension slightly below what is desired , and then using a expander to raise that diameter to the desired dimension , for proper neck interference , (neck tension ) . And this process makes ALL of the cases more consistent across the group of cases being worked .
RegionRat
Gold $$ Contributor
Brass is similar to many other materials in that it has a modulus of elasticity and also a yield strength. And not to take us all down an advanced engineering rat hole, that modulus term contains a shear storage and shear loss term. I bring that up now at risk, because it is important. Those loss terms have a different place in the equations than the normal damping terms that are purely speed related. They are not easy to observe independently so the concepts are hard to teach.
These effects are huge and “easy to see” in polymers and playing them to their advantage is why some materials make good dampers and others make better springs. However, brass also has some of these damping, storage, and loss properties.
The reason to bring them up is to shed light on how different the neck prep can be between a tight neck bench rest rig at one extreme and a sporting rig at the other. Allowing the strain value to go well past yield versus just barely into yield is the essence of the question of why some folks don’t “see the purpose“ or need for a mandrel while others depend on them.
The key to beginning to understand those issues is to watch the size of the strain against how much of that will be elastic versus plastic. These discussions change in the third and fourth decimal point by caliber, but size and step size matters.
You end up drilling down on how big each size change operation is, and how big the next one would be in order to use those yield and elastic properties to your advantage, while also trying to avoid over working the brass.
When you fire brass in a typical sporting chamber, your neck diameter goes way past the yield point and then the elastic portion brings that diameter down a little. Comparing that to a bench rest neck that has been turned thinner, and to that tight necked chamber, give us a different task with different amounts of bushing or mandrel diameter to get us back to the neck prep goal.
When you size a neck, the amount or that size step makes a difference. If your bushing pushes your brass well beyond yield, there will still be some amount of elastic recovery. The shear storage and shear loss terms buried inside of that modulus term get affected by the speed and size of that working. To put it in bottom line terms, sometimes the amount and speed of the strain will change the outcome such that your finished diameter doesn’t move the same amount based in the history of that brass.
So if your bushing places the inside diameter of the neck very close to the finished diameter goal, a mandrel may not have any effect until it pushes back out enough to hit the yield point. The different caliber diameters can affect how big any given change must be in order to hit yield, so one must play with sizing processes to get to their goals. The only advice I can give has to to with getting enough small step sizes in bushings and mandrels to have the latitude to play with your particular set up. Mandrels work just like bushings, just the other direction. YMMV
These effects are huge and “easy to see” in polymers and playing them to their advantage is why some materials make good dampers and others make better springs. However, brass also has some of these damping, storage, and loss properties.
The reason to bring them up is to shed light on how different the neck prep can be between a tight neck bench rest rig at one extreme and a sporting rig at the other. Allowing the strain value to go well past yield versus just barely into yield is the essence of the question of why some folks don’t “see the purpose“ or need for a mandrel while others depend on them.
The key to beginning to understand those issues is to watch the size of the strain against how much of that will be elastic versus plastic. These discussions change in the third and fourth decimal point by caliber, but size and step size matters.
You end up drilling down on how big each size change operation is, and how big the next one would be in order to use those yield and elastic properties to your advantage, while also trying to avoid over working the brass.
When you fire brass in a typical sporting chamber, your neck diameter goes way past the yield point and then the elastic portion brings that diameter down a little. Comparing that to a bench rest neck that has been turned thinner, and to that tight necked chamber, give us a different task with different amounts of bushing or mandrel diameter to get us back to the neck prep goal.
When you size a neck, the amount or that size step makes a difference. If your bushing pushes your brass well beyond yield, there will still be some amount of elastic recovery. The shear storage and shear loss terms buried inside of that modulus term get affected by the speed and size of that working. To put it in bottom line terms, sometimes the amount and speed of the strain will change the outcome such that your finished diameter doesn’t move the same amount based in the history of that brass.
So if your bushing places the inside diameter of the neck very close to the finished diameter goal, a mandrel may not have any effect until it pushes back out enough to hit the yield point. The different caliber diameters can affect how big any given change must be in order to hit yield, so one must play with sizing processes to get to their goals. The only advice I can give has to to with getting enough small step sizes in bushings and mandrels to have the latitude to play with your particular set up. Mandrels work just like bushings, just the other direction. YMMV
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