April 14th, 2018

Reloading Tip: Use Expander Mandrels with New Brass

Expander Mandrel reloading case neck tension cartridge brass

Before you load that nice new cartridge brass for the first time, run an expander mandrel down the case necks. This will iron out dents and provide more uniform neck tension. Chose a mandrel diameter that provides appropriate neck tension.

Lapua brass is so good that you’ll be tempted to just load and shoot, if you have a “no-turn” chamber. However, some minimal case prep will ensure more uniform neck tension. Keeping your neck tension very uniform allows more consistent bullet seating. That, in turn, usually yields better accuracy, and lower Extreme Spread and Standard Deviation (ES/SD). Lapua brass, particularly 6mmBR, 6.5×47, 6.5 Creedmoor, and .308 Win comes from the factory with tighter-than-optimal necks. Before you seat bullets, at a minimum, you should inside chamfer the case mouths, after running an expander mandrel down the necks. The expander mandrels from both Sinclair Int’l and K&M will both leave the necks with enough neck tension (more than .001″) so you can then seat bullets without another operation. We suggest putting a bit of lube on the mandrel before running it down the necks — but remove any lube that gets inside the necks before seating bullets.

Sinclair Expander Tool Mandrel

Both Sinclair and K&M Tools make a die body specifically to hold expander mandrels. The Sinclair version, is shown above. This $28.99 unit fits caliber-specific expander mandrels ($9.99) which measure approximately .001″ less than bullet diameter for each caliber. This is an updated “Gen II” design that completely captures the mandrel within the die so the mandrel cannot pull out. It also has an O-ring in the die cap that allows the mandrel to self-center within the case neck. Sinclair now offers three sizes of die bodies for expander mandrels: .17 -.338 Caliber (#749-011-715WS); .357 – .50 caliber (#749-008-843WS), and a special .50 Cal die body for large-diameter 50 BMG presses (#749-009-163WS, $39.99). All Generation II dies are machined from stainless steel and the standard diameter 7/8-14 dies include the Sinclair Stainless Steel Split Lock Ring.

Once you run the Sinclair expander mandrel down the necks of Lapua brass, after you account for brass spring-back, you’ll have about .002″ neck tension*. This will make the process of seating bullets go much more smoothly, and you will also iron out any dents in the case mouths. Once the case mouths are all expanded, and uniformly round, then do your inside neck chamfering/deburring. The same expander mandrels can be used to “neck-up” smaller diameter brass, or prepare brass for neck-turning.

Forum member Mike Crawford adds: “These expanders can also reduce runout from offset seating. Prior to bullet seating, expand the sized necks to force thickness variance outward. With the Sinclair system, the necks will springback fine, and will not be pulled out of center. This leaves plenty of tension, and bullets seated more centered. I do this, even with turned necks, to get improved seating.”

Mandrels vs. Expander Balls on Decapping Rods
If you haven’t acquired an appropriate expander mandrel for your brass, but you DO have a full-length sizing die with an expander ball, this will also function to “iron out” the necks and reduce tension. However, using a die with an expander ball will work the necks more — since you first size them down, then the ball expands them up again. Typically (but not always), run-out is worse when using an expander ball vs. an expander mandrel.


* This .002″ tension is what we have observed with Lapua 6mmBR, 6.5×47, 6.5 Creedmoor, and .308 Win brass. This might vary with much smaller or larger cases, and of course a different brand of brass might yield different results. If you get too little tension with your current mandrel, you can get a smaller-diameter mandrel from 21st Century Shooting. 21st Century even offers low-friction Titanium Nitride-coated mandrels.

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August 26th, 2013

K&M Ported Expander Mandrel Riser and Neck-Turner Grip

K&M PrecisionK&M Precision Shooting Products has two very handy products you may not know about yet. The first, a brilliantly simple device that lets you see your case necks as you expand them, can be used by anyone who necks-up brass (with a compatible expander die body). The second new product is a specialized “fat grip” holder that will make neck-turning easier for those of you out there who use K&M neck-turners.

K&M Expand Mandrel Window Riser
This is a simple threaded extension placed between your expander die body (K&M Expand Iron) and the top of your press. It carries the expander mandrel higher, above the press, and has a cut-out view port so you can see the mandrel as it passes through the neck. Smart, eh? This provides visual feedback during the process of expanding your brass. The patent-pending view riser costs $20.00. Will it expand necks faster, or reduce run-out? We doubt it, but we still would like to have one, if only to eyeball the mandrel to control the neck-entry rate more consistently from case to case.

K&M Expander Riser

Installation: Thread the Expand Mandrel Window Riser into the top of your loading press, then thread the K&M Expand-Iron (Expander Die Body) fully into the top of the window riser and adjust each so you can stroke out the press completely without driving the case mouth into the press adapter. This allows you to view the expanding operation which is typically blind under the press. The riser also eliminates the need for the stop screw in the expander mandrel. LINK: Expand Window Riser Instructions (PDF).


Ergo Holder K&MErgo Holder for K&M Neck-Turning Tool
K&M’s rounded, oversized Ergo Holder lets you hold the K&M neck-turning body more securely (and with less hand cramping). Priced at $35.00, it is an expensive accessory, but we suspect many guys with K&M neck-turners will spring for an Ergo holder just because it gives you a more secure and comfortable grip on the small, square-edged K&M neck-turner.

Customer Feedback Inspired K&M’s Ergo Holder
The folks at K&M told us that their new Ergo Holder was produced in response to customer requests: “[Customers reported that] the neck turner can be hard to hold due to its compact size, especially in high-volume use. The Ergo Holder is machined from aluminum, providing a fatigue-proof grasp of the neck turner. Its mass works like a heat sink to help dissipate heat from the pilot during the turning process. The neck-turner body easily assembles into the Ergo Holder and is held in place with one set screw. The Ergo holder is also designed with the dial indicator in mind and actually makes its use more convenient”.
LINK: Ergo Holder Installation/Use Instructions (PDF).

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