May 25th, 2007

Expander Tool for New Brass

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. This will produce better accuracy, more consistent bullet seating, and lower Extreme Spread and Standard Deviation (ES/SD). Lapua brass, particularly 6BR, 6.5×47, .243 Win 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 and K&M will both leave the necks with enough neck tension (more than .001″) that you can then seat bullets without another operation. Put 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.

Both Sinclair and K&M Tools make a die body specifically to hold expander mandrels. The Sinclair version, item NT-EXP, is shown below. This $17.90 unit fits caliber-specific expander mandrels ($7.95) which measure approximately .001″ less than bullet diameter for each caliber. 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. Note: an alternative to this procedure is to full-length size every case with an expander ball in place, prior to loading. That works too, but many reloaders may prefer to simply expand the necks, when using Lapua brass.

Sinclair Expander Tool Mandrel

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