November 17th, 2018

Case Grip on Bullet — There’s More to Neck Tension Than Just Bushing Size

case neck bushing reloading die tension bullet release

Many novice hand-loaders believe that neck bushing Inside Diameter (ID) size is the only important factor in neck tension. In fact, many different things will influence the grip on your bullet and its ability to release from the case neck. To learn more about neck tension and “case grip”, take the time to read this article carefully. We bet you’ll gain knowledge that will let you load more accurate ammo, with better ES/SD.

Neck Tension (i.e. Grip on Bullets) Is a Complex Phenomenon
While we certainly have considerable control over neck tension by using tighter or looser bushings (with smaller or bigger Inside Diameters), bushing size is only one factor at work. It’s important to understand the multiple factors that can increase or decrease the resistance to bullet release. Think in terms of overall brass-on-bullet “grip” instead of just bushing size (or the internal neck diameter in non-bushing full-length sizing dies).

Bullet grip is affected by many things, such as:

1. Neck-wall thickness.
2. Amount of bullet bearing surface (shank) in the neck.
3. Surface condition inside of neck (residual carbon can act as a lubricant; ultrasonic cleaning makes necks “grabby”).
4. Length of neck (e.g. 6mmBR neck vs. 6mm Dasher).
5. Whether or not the bullets have an anti-friction coating.
6.The springiness of the brass (which is related to degree of work-hardening; number of firings etc.)
7. The bullet jacket material.
8. The outside diameter of the bullet and whether it has a pressure ridge.
9. Time duration between bullet seating and firing (necks can stiffen with time).
10. How often the brass is annealed.
11. Amount (length) of neck sized (e.g. you can size only half the neck).
12. Interior diameter of bushing, or neck section of non-bushing die.

— and there are others…

One needs to understand that bushing size isn’t the beginning and end of neck tension questions, because, even if bushing size is held constant, the amount of bullet “grip” can change dramatically as the condition of your brass changes. Bullet “grip” can also change if you alter your seating depth, and it can even change if you ultrasonically clean your cases.

Redding neck bushingsIn our Shooters’ Forum a reader recently asked: “How much neck tension should I use?” This prompted a Forum discussion in which other Forum members recommended a specific number based on their experience, such as .001″, .002″, or .003″. These numbers, as commonly used, correspond to the difference between case-neck OD after sizing and the neck OD of a loaded round, with bullet in place. In other words, the numbers refer to the nominal amount of interference fit (after sizing).

While these commonly-used “tension numbers” (of .001″, .002″ etc.) can be useful as starting points, neck tension is actually a fairly complex subject. The actual amount of “grip” on the bullet is a function of many factors, of which neck-OD reduction during sizing is just one. Understanding these many factors will help you maintain consistent neck tension as your brass “evolves” over the course of multiple reloadings.

Seating Depth Changes Can Increase or Decrease Grip on Bullet
You can do this simple experiment. Seat a boat-tail bullet in your sized neck with .150″ of bearing surface (shank) in the neck. Now remove the bullet with an impact hammer. Next, take another identical bullet and seat it with .300″ of bearing surface in another sized case (same bushing size/same nominal tension). You’ll find the deeper-seated bullet is gripped much harder.

PPC lapua brassNeck-Wall Thickness is Important Too
I have also found that thinner necks, particularly the very thin necks used by many PPC shooters, require more sizing to give equivalent “grip”. Again, do your own experiment. Seat a bullet in a case turned to .008″ neckwall thickness and sized down .003″. Now compare that to a case with .014″ neckwall thickness and sized down .0015″. You may find that the bullet in the thin necks actually pulls out easier, though it supposedly has more “neck tension”, if one were to consider bushing size alone.

In practical terms, because thick necks are less elastic than very thin necks, when you turn necks you may need to run tighter bushings to maintain the same amount of actual grip on the bullets (as compared to no-turn brass). Consequently, I suspect the guys using .0015″ “tension” on no-turn brass may be a lot closer to the guys using .003″ “tension” on turned necks than either group may realize.

Toward a Better Definition of Neck Tension
As a convenient short-cut, we tend to describe neck tension by bushing size alone. When a guy says, “I run .002 neck tension”, that normally means he is using a die/bushing that sizes the necks .002″ smaller than a loaded round. Well we know something about his post-sizing neck OD, but do we really have a reliable idea about how much force is required to release his bullets? Maybe not… This use of the term “neck tension” when we are really only describing the amount of neck diameter reduction with a die/bushing is really kind of incomplete.

My point here is that it is overly simplistic to ask, “should I load with .001 tension or .003?” In reality, an .001″ reduction (after springback) on a thick neck might provide MORE “grip” on a deep-seated bullet than an .003″ reduction on a very thin-walled neck holding a bullet with minimal bearing surface in the neck. Bushing ID is something we can easily measure and verify. We use bushing size as a descriptor of neck tension because it is convenient and because the other important factors are hard to quantify. But those factors shouldn’t be ignored if you want to maintain consistent neck tension for optimal accuracy.

Consistency and accuracy — that’s really what this all about isn’t it? We want to find the best neck tension for accuracy, and then maintain that amount of grip-on-bullet over time. To do that you need to look not only at your bushing size, but also at how your brass has changed (work-hardened) with time, and whether other variables (such as the amount of carbon in the neck) have changed. Ultimately, optimal neck tension must be ascertained experimentally. You have to go out and test empirically to see what works, in YOUR rifle, with YOUR bullets and YOUR brass. And you may have to change the nominal tension setting (i.e. bushing size) as your brass work-hardens or IF YOU CHANGE SEATING DEPTHS.

Remember that bushing size alone does not tell us all we need to know about the neck’s true “holding power” on a bullet, or the energy required for bullet release. True bullet grip is a more complicated phenomenon, one that is affected by numerous factors, some of which are very hard to quantify.

Permalink Bullets, Brass, Ammo, Reloading, Tech Tip 2 Comments »
November 17th, 2018

Get FREE Reloading Data Sheets and Ammo Box Label Templates

Reloading Data Form Ammo Box Template printing labels chronograph data sheet

Redding Reloading offers handy Handloader’s Data Sheets in printable PDF format. This FREE form allows hand-loaders to document their tool settings, bushing size, powder charge, load specs (COAL etc.), and case prep status. In addition, the form allows you to enter your load testing information, complete with chronograph data, group size, zero range, and wind/temp conditions. With this single, handy form you can document all the vital information for your particular cartridges and loads. We suggest you print these out, 3-hole-punch ‘em, and then keep them in a three-ring binder.

Download FREE Handloader’s Data Sheet (PDF)

We’ve seen various reloading log templates, but this Redding form (shown below) is better than most because it combines both reloading data AND range-test data in one place. You can see all key details of the reloading process (tool settings etc.) plus the end results — how the load actually performed over the chronograph and on paper. This form allows the user to capture a large amount of information for later use, while accurately track load development. Go to Download Page.

Reloading Data Form Ammo Box Template printing labels chronograph data sheet

FREE Ammunition Box Label Template
Reloading Data Form Ammo Box Template printing labels chronograph data sheetRedding Reloading has also developed a printable template for your ammo boxes (see photo at top of article). This lets you put all vital load info on your ammo boxes. There are fields for: Date, Cartridge, Powder, Grains, Bullet, Weight, Primer, Case type. Designed for Avery 5260 (or similar) label sheets, this template allows you to print 30 labels at one time. You can purchase the Avery 5260 peel-off printable label sheets at any office supply store.

Download Box Label Template (PDF)

Permalink Bullets, Brass, Ammo, Reloading 1 Comment »
November 17th, 2018

Make Your Own Ammo Caddy with Wood Knife-Holder Block

Wood Knife Holder ammo caddy

Forum member Alex W. (aka “zfastmalibu”) came up with a clever adaptation of an item you may already have on your kitchen counter. By drilling a few strategically-placed holes in a wood knife-holding block, Alex created a handy, 20-round ammo holder for the bench. We’re not sure the wife will appreciate the new holes in her kitchen accessory, but we think this is a smart invention. Alex asked fellow Forum members: “What do you think, is there a market for it?” We think there is. Of course, with a ruler and an electric drill you could probably make your own version easily enough.

Get a Solid Wood Knife Block for under $25.00
Hardwood Knife blocks can be purchased for under $25.00 through Amazon.com. They are also available in bamboo ($18.14), beechwood ($39.95), acacia ($49.95), and solid walnut ($59.95).

Permalink Gear Review, Tech Tip 1 Comment »