Expand Mandrels for Bullet Tension

(3 customer reviews)


Bullet Tension Mandrels: 
•Now stocking most sizes – we aim to ship next business day!
•Less common sizes ship ~1-2 weeks from date of purchase
•See Description Section for details
•Many* expand mandrels are the new PowerStroke™ model without a stop screw: .22, 6mm, 6.5mm, .270, 7mm, .30, .338, .375, .416, .45 and .50 cal
   (*some sizes may still have the threaded hole as we deplete inventory)
PowerStroke™ expand mandrels require a v1 Window Riser or v2 Press Adapter – help me choose.
For custom size expand mandrels, please e-mail to order. 


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Expand Mandrels for Bullet Tension:

Tool Notes: Download Tool Instructions

After selecting the caliber, select each bullet tension expand mandrel desired for your kit.  Each selection allows for selecting an etched press adapter and the corresponding gage pin for that neck tension.  Both the expand mandrel and the press adapter are laser-etched with the caliber and the bullet tension for easy identification.  The gage pin block will be etched with the caliber and each gage pin location will be noted with the bullet tension and the diameter of the gage pin.  All of our expand mandrels are ground oversize to account for spring-back of brass which is assumed at the nominal anneal.

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.  For example, say you are working with a 7mm caliber (0.284”) and you would like 0.004” of bullet tension.  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.  Now subtract the 0.002” or 0.003” from the final size, 0.280”-0.003”=0.277”.  Now based on your neck wall thickness select the appropriate bushing that will achieve the 0.277” inside neck diameter.  Once this sizing is complete perform the final sizing of the neck with the expand mandrel.  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.

Checking your Case Neck with Gage Pin:

 After expanding use the corresponding gage pin to confirm the neck sized as expected.  The feel you are looking for is a light drag on the gage pin.  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.  You can actually feel the air compress inside the case.  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 pin gage.

3 reviews for Expand Mandrels for Bullet Tension

  1. Paul Anderson (verified owner)

    All the K&M products I’ve put on the shelf in my shop are superb. Exacting precision is what you get with these folks.

  2. rweeks7mm (verified owner)

    I purchased the Expander Mandrel Window Riser and a custom 7mm Remington Magnum mandrel for 0.002″ neck tension. Fit and finish was excellent. Shipping was fast even though this was a custom part and I purchased close to Christmas. I have not had a chance to test any loads made with it yet, but brass sized with it were inline with the spec. Thanks again to K+M for another great purchasing experience.

    • Dave @ K&M

      Rweeks7mm, thanks for the review and feedback! Happy reloading.

  3. Scott Posey (verified owner)

    Don’t expect anything more. Spot on products.

    • Dave @ K&M (verified owner)

      Thanks for the review Scott; glad we’re hitting the mark!

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