K&M Precision PowerStroke Expander Mandrel Set
The K&M Precision PowerStroke™ Expander Mandrel Set is the next generation tool for expanding case necks to the correct neck tension and concentricity. This complete system works on virtually all types of reloading presses and is fully compatible with coax presses. For the precision reloader who wants full control over neck tension, the PowerStroke is an indispensable addition to the reloading bench.
Benefits of the PowerStroke
The PowerStroke expander mandrel works the brass from inside out, resulting in minimal deformation and an extremely consistent inner diameter of the case mouth. Unlike a standard expander ball in a reloading die, the mandrel glides smoothly through the neck without unnecessarily stressing the brass.
The result is uniform neck tension on every bullet you seat. This consistency translates directly to lower extreme spread (ES) and standard deviation (SD) of your muzzle velocity. For F-Class, benchrest and PRS shooters striving for the tightest possible groups, this is a noticeable difference on target.
Set contents
This complete PowerStroke set contains all components to start immediately:
- PowerStroke (V2) 2-Row press adapter
- PowerStroke Mandrel holder
- 7/8-14 lock ring
- 5/8-18 lock ring
- Mandrel of your choice (also available separately)
How expanding works
When using an expander mandrel for final neck diameter, keep the neck size 0.002" to 0.003" below the desired final dimension. A practical example for 7mm calibre (0.284") with a desired neck tension of 0.004":
Subtract the neck tension from bullet diameter: 0.284" - 0.004" = 0.280" (this is your final dimension after expanding). The inner diameter of the neck must be slightly smaller so the mandrel can correctly form the brass. Subtract another 0.002" to 0.003": 0.280" - 0.003" = 0.277". Then select the correct bushing based on neck wall thickness to achieve this neck diameter.
Alternatively, you can use a full-length sizing die with the expander ball removed and use the mandrel for final sizing. Always use a light lubricant when expanding.
Checking with a gauge pin
After expanding, check the neck dimension with the corresponding gauge. The correct feel is slight resistance on the gauge pin. At the correct dimension, the gauge pin works like a piston when you push it into the case while holding a finger over the primer pocket. You feel the air compress inside the case.
Brass is sometimes harder or softer than expected. By increasing or decreasing the mandrel diameter, you can fine-tune the desired neck tension to the perfect result.
Specifications
- Brand: K&M Precision
- Model: PowerStroke™ Expander Mandrel Set
- Version: V2 (2-Row press adapter)
- Compatibility: virtually all reloading presses, including coax presses
- Set contents: press adapter, mandrel holder, 7/8-14 lock ring, 5/8-18 lock ring, mandrel of choice
- Mandrels: also available separately in various diameters
- Application: expanding case necks for uniform neck tension and concentricity
- Manufacture: Made in USA
- Manufacturer: K&M Precision
