K M Neck/Bullet Tension Expanding Mandrel

Description Use an expanding mandrel to achieve the desired neck tension. Be sure to use a light lubricant. Choosing the mandrel size: For example, say you are working with a 7mm caliber (0.284”) and you would like 0.002” of bullet tension, subtract the 0.002” from the standard bullet diameter, 0.284”-0.002”= 0.282”. Choose this expanding mandrel size to obtain the desired bullet tension. Use the chart below for your caliber. Currently we stock the mandrels to achieve 0.001″, 0.002″ and 0.003″ neck/bullet tension. Should you require a different size, please contact us, and we will add it to our next order. For larger calibers click here Bullet tension chart for calibers .17 to .33 Checking your Case Neck with Gage Pin that can be found here: 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.  By stepping up or down on the expand mandrel bullet tension size you can achieve the desired neck tension to your pin gage. Currently we stock the gage pins to measure 0.001″, 0.002″ and 0.003″ neck/bullet tension. Should you require a different size, please contact us, and we will add it to our next order.