neck turning & neck tension


Here are some of my insights into case neck turning and case neck tension. I strive to load the most accurate hunting rounds possible; my hobby, my perfectionism, my drive for continuous improvement and compensation for being an average marksman. The reality is that no matter how good your equipment is, it counts for zero if you cannot use it. When I encounter problems I get to understand the root cause of the problem in order to avoid repeat issues. The purpose of the blog is not information on setups or procedures, such information is available in many forms, but to share some of my practical findings that may help you.

Case neck turning is performed for accuracy improvement or when the need arises to cut away excess brass flow at the neck and shoulder junction (after multiple loads). I will discuss the elements of accuracy; if a need then no discussion, just do it. Uniform neck turning will contribute to improved bullet seating concentricity (provided case alignment) and uniform neck tension around the circumference of the bullet. The need for neck turning is largely influenced by the quality of brass being used. I find less benefit in turning Laupa and Norma case necks because their uniformity is good anyway. If you don’t want to outside neck turn cases then as a minimum buy quality brass.

I find the benefit of case neck turning to be minimal for bigger calibers. I have loaded a lot of 9.3 x 62, 9.3 x74R and 375 H&H; all shot sub MOA groupings without any neck turning or any special case sizing procedure. Given good accuracy results and given that these are hunting calibers used for shorter shooting distances I have stopped neck turning on bigger bores. I do not use sizing dies that require neck bushings nor do I use expanding mandrels in any of these bigger bores. I condition this practice with using quality brass. I have found loading for bigger slower calibres easier than for smaller higher velocity calibers. I found slower bigger calibers shoot better groups across a wide spectrum of bullet weights compared with smaller high velocity calibers.

Let’s now focus on the smaller bores. There is no absolute transition point because the application is more relevant in deciding the extent of case preparation. I have found bullet concentricity to have a significant influence on accuracy; I have not yet experimented with the influence of uniform neck tension on accuracy. I outside neck turn for reasons of bullet concentricity rather than for benefits in accuracy of uniform neck tension. Bench rest shooters and long distance shooters take every step in case preparation to ensure maximum uniformity because accuracy deviations are exacerbated in long range shooting.

Neck tension is the amount of grip the case neck has on the bullet. We are focused on smaller calibers hence crimping is not considered. I am not going to try define what the case neck tension should be because this varies between bench rest shooting, single shot rifles, hunting conditions, higher recoil calibers etc. Directionally bench rest shooters prefer less neck tension whereas hunting conditions or higher recoil calibers require more neck tension in order to avoid bullet creep in the field or in a magazine under recoil. I recommend that you experiment in neck tension for your particular rifle and use.

Neck tension is determined by how much smaller the inside diameter of the case neck is after sizing compared to the diameter of the bullet being seated. Case neck inside diameter should be in the range of about 0.01” to 0.04” less than the bullet diameter depending on application (and gun preference). For me what is more important is to keep the same neck tension from batch to batch after achieving a good load. Ensuring the same neck tension for all rounds is another reason why I trim cases after every resize to ensure case neck length uniformity.

You need to approach neck tension based on the equipment being used. If you are using competition type dies with neck bushings then you need to select the bushing size that gives the case neck tension desired. Selecting the proper bushing requires an accurate measurement of the case neck wall thickness. Be aware of the change in case neck wall thickness if changing the brand of brass or performing outside neck turning. My purpose is not to write about the different ways to select the bushing size (many articles on how) but to highlight those variables which may influence your choice of the reloading process; it certainly changed how I reload.

My trial (or stupidity) in trying to optimize case neck concentricity by removing the expander ball showed the effect of too much case neck tension. In an attempt to avoid the risk of case misalignment when the expander ball pulls back through the neck after the neck was down sized on the down stroke, I removed the expander ball. When I seated the bullets I had excess run-out, poor concentricity. The cause was too much neck tension on seating which impacted the bullet alignment. The inside neck diameter was too small compared to the bullet diameter.

I have many competition sizing dies with neck bushings but became frustrated by the variables in case wall neck thickness; hence I sought a method similar to the function of the expander ball but without the risk of case neck misalignment. What I like about an expander ball is that the inside case neck diameter is always the same after sizing irrespective of case neck thickness (same neck tension). I therefore added a step in my loading procedure that achieves the same as the expander ball in the sizing die but without the risk of case misalignment:

1. I remove the expander ball from the resizing die when sizing,
2. I use an expander die body fitted with expander mandrel to expand the inside case neck to a uniform inside diameter. Case neck alignment unaffected.

Expander die bodies, short & long, plus numerous of my expander mandrels

Expander die bodies, short & long, plus numerous of my expander mandrels

A valuable lesson learnt with this procedure, it is important that the case does not bottom out on the expander body die, this will impact case neck concentricity. Set the expander body die in the press so it cannot bottom out. I always check a sample of cases for concentricity after the different reloading steps to catch a concentricity problem before starting a further step in the process.

It would be amiss of me not to point out that if you always used brass of the same case neck wall thickness then sizing with a properly selected bushing would achieve the same outcome without the additional reloading step I perform with the expander mandrel. In this way you eliminate 100% of the risk of case neck misalignment provided you use precision quality bushings. I have bushings in a range of +- 0.01” hence I could change the bushing with small variations in case wall neck thickness but the reality is I find it difficult to get accurate case neck wall measurements.

precision measuring equipment to measure case neck wall thickness

precision measuring equipment to measure case neck wall thickness

I have travelled a full circle on outside neck turning. I started with the Forster hand held tool, then I bought the 21st Century lathe system with different cutter angles to prevent cutting into the shoulder. “Fancy” and it works well, but I use it less and less. I prefer to use quality brass and cut out on some of the need to outside neck turn. I always focus on concentricity and hence I perform the additional step of case neck expansion with an expanding mandrel on the smaller higher velocity calibers. Uniform neck thickness achieved with outside neck turning does contribute to bullet seating concentricity but with good brass I find the benefit minimal for hunting purposes.

I will close with a hunting lesson and habit that came out of reloading, but probably more my personality. I spend a lot of effort in brass preparation and care, I retrieve every fired brass from my rifle. At a recent pig hunt in Croatia I shot a running bore at 5m with a 9.3×62. My shot was slightly forward which swung the boar around to face me at 5m. I did not work the bolt like a bolt should be worked and this pussy had a jam and a wounded boar staring him down. I looked for a tree, but lady luck, there was Ales who saved my bacon. The lesson is obvious, forget about your brass in hunting situations, live for the hunt and not the brass.

Forget about your cases when shooting dangerous game - work your bolt like a bolt was designed to work

Forget about your cases when shooting dangerous game – work your bolt like a bolt was designed to work