KM Expander Mandrel V1


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KM STD Expander Mandrel – Neck turning preparation

The KM Expander mandrels bolt into a special press adapter to be used to internally expand (usually virgin brass) prior to neck turning operations using the KM Neck Turners.
These expanders fit into the KM Press Adapter (sold separately)
They are sized approximately 0.001″ larger than the KM brand neck turner mandrels (all 3 types of KM neck turn mandrels). Which means they are either on calibre size or 1/2 thousandths larger.
This is to allow for brass spring back of new cases giving a good fit of the inside necks on those mandrels. Without a proper fit the final results of outside neck turning will provide variations.
The actual size of the KM expanders is usually close to actual caliber size (eg: for 30cal will be 0.308″, for 6mm will be 0.243″)These expanders have a unique depth control adjustment also. Set to bottom out on the inside case web. This means they can also be adjusted carefully to assist in removal of internal case neck ‘donuts’ by expanding down to, but not over the ‘donut’. (separate tools required to cut out donuts)

NB: KM are changing slightly the expanders which they are now supplying. New versions DO NOT have the threaded adjustment rod. They call these the “powerstroke expanders” just to identify them differently. The only difference between them is the threaded rod or not. But with any expander having a threaded rod (as per photos) you can unscrew and remove it. Therefore it becomes the same as a non threaded unit. For best height adjustments use either of the two new V2 Powerstroke press adapters (two heights available).

* Therefore, a quote from the manufacturers website…. “some sizes may still have the threaded hole as we deplete inventory”


NB: For other expanding operations, to uniform inside of necks and control bullet grip after resizing (especially using Neck bushing type dies) the KM Custom undersize mandrels are made for those tasks (separate product). Those Custom undersize expanders are a ground to size tools and are very consistent size. Therefore they more expensive.

These STD expanders in this group are machined to size and therefore will be slight size variations.


What’s included? 1 x Expander mandrel and securing bolt for the press adapter (press adapter are sold separately).
Also consider a Window riser for the STD press adapter or a new style V2 Powerstroke press adapters (sold separately)


New Power Stroke style is being introduced as old styles are selling out.

(6mm-30cal, 172, 204, 224, 243, 257, 264, 277, 284, 308, 311, 315, 338. 357, 366, 375, 408, 416)