Expand Mandrel Prebuilt Kits

(1 customer review)



Select Caliber, then Kit Type
See Description section for Kit contents and details.


Kit Contents:

.17 – .338 cal .35 – .50 cal

Starter Kit:

Range Kit: (Including Starter Kit Items)

Full Kit: (Including Starter + Range Kit Items)

Starter Kit:

Range Kit: (Including Starter Kit Items)

Full Kit: (Including Starter + Range Kit Items)

Both the expand mandrel and mandrel holder are laser-etched with the caliber and the bullet tension for easy identification.Β  The gage pin block is etched with the caliber and each gage pin location noted with the bullet tension and the diameter of the gage pin.Β  All of our expand mandrels are ground to account for spring-back of brass which is assumed at the nominal anneal.

Checking your Case Neck with Gage Pins:

Β After expanding use the corresponding gage pin to confirm the neck sized as expected.Β  The feel you are looking for is a light drag on the gage pin.Β  When sized properly the gage pin will act as a piston as you push the pin into the case neck while holding your finger or thumb over the primer pocket.Β  You can actually feel the air compress inside the case. Β Quite often the brass can be harder or softer than expected. By stepping up or down on the expand mandrel bullet tension size you can achieve the desired neck tension to your gage pin.

Tool Instructions: Neck Expanding

When using an expand mandrel to achieve final neck sizing bullet tension we find it best to size your neck 0.002” to 0.003” below your desired final bullet tension size.Β  For example, say you are working with a 7mm caliber (0.284”) and you would like 0.004” of bullet tension.Β  Subtract the 0.004” from the standard bullet diameter, 0.284”-0.004”=0.280”, this will be the final size after expanding. However, the neck inside diameter needs to be slightly smaller so the expand mandrel can properly size the brass.Β  Now subtract the 0.002” or 0.003” from the final size, 0.280”-0.003”=0.277”.Β  Now based on your neck wall thickness select the appropriate bushing that will achieve the 0.277” inside neck diameter.Β  Once this sizing is complete perform the final sizing of the neck with the expand mandrel.Β  Be sure to at least use a light lubricant. Alternatively, you can use a traditional full-length die (expander ball removed) and use the expand mandrel for final sizing.

Available Accessories:

1 review for Expand Mandrel Prebuilt Kits

  1. DAVID CROXTON (verified owner)

    This set help you get the exact neck tension you need to get the “one hole” group. Very easy to use and to know which neck tension setup give you the best and consistent groups.

    • Dave @ K&M

      Thanks for the review David! Please let us know if have any suggestions for continuous improvement! Email us at [email protected].

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