Paul Box, Ballistic Technician at Sierra BulletsNeck tension is a key factor in creating an accurate load [it’s one of the factors that determines the “grip” of a bullet]. I think that a lot reloaders take this for granted, and don’t really give it much thought. How much neck tension do you think is sufficient? Over the years, and with a variety of calibers, I have found that.002″ of neck tension has given me the best overall accuracy. You will find rifles that perform better with.001″ or.003″ of neck tension, but for me.002″ has worked well. How do we control neck tension? Let’s have a look. If you’re using a standard die with an expanding ball, simply remove the decapping rod from your die to measure the ball. For starters, I like to have an expansion ball that is.003″ smaller than the bullet diameter. For example, in a caliber of.224, you would run an expander-ball diameter of.221″. If you need to reduce the diameter of the expander ball, simply put your decapping rod in a drill. Then use some emery fabric to turn it down. Once you have the desired diameter, polish it using three or four ounces of steel wool. This will give your case neck a more reflective finish and reduce the drag. Tips for Dies with Interchangeable Neck Bushings
If you are using a bushing-die, I measure the neck of 8 or 10 loaded rounds. Then, I take an average and subtract.003″ from that measurement. This system has worked for me. There are other ways to determine bushing sizes, but I’ve found this one to be the most accurate. Proper Annealing Can Deliver More Uniform Neck Tension
Annealing is another thing I would like to mention. Brass that is soft enough will “set” better when it comes out of the sizing tool than brass that is too hard. When brass is work hardened, it will be springier when it comes out of the sizing die. The neck tension will also vary. Have you ever noticed that some bullets seat harder than others? This is why. You will get better accuracy and more consistent groups if you pay attention to the neck tension.
