How Brass Neck Turning Effects Handload Accuracy
October 31, 2019
What turning necks can (and can't) do for the accuracy of your handloads.
As with most performance-oriented activities, gaining the final few percent of accuracy typically demands ever-increasing tribute in terms of dollars and effort. Neck turning falls into the “effort” category. Is it really beneficial? And if so, is it beneficial in all cases or just in isolated cases? Assuming the latter, is there a way to predict benefit before the fact?
If one side of a case neck is thicker than the other, it is less elastic. When the gunpowder detonates, the two sides—of differing thickness—exert differing forces on the projectile as it exits the neck and mouth of the case. Differing forces are bad when it comes to accuracy.
Further, if the case neck is appreciably thicker on one side than on the other, it biases the cartridge’s positioning within the chamber, meaning it presents it into the rifling slightly off- center. Yes, the projectile will always have some bias introduced by gravity, but additional bias introduced by inconsistent neck thickness adds more variation. Also bad.
Benchrest shooters more or less eliminate off-center positioning with chambers that are cut very tight. That’s necessary to win matches but impractical for most types of shooting in the field, whether on game or on targets.
You can also seat projectiles far enough out that they contact the rifleing leade. This self-centers them, but it can result in the bullet being stuck in the chamber—a disaster in the hunting fields.
And then there’s neck turning. It is a lot of work, but it often provides a tangible accuracy increase. All of the tightest groups I’ve ever fired came with neck-turned cases. That may be anecdotal, but it’s enough for me, and it’s worth noting that all benchrest shooters—even though they’ve taken one or both of the steps I just described—neck turn their brass. If it wasn’t helpful, they wouldn’t do it.
So that moves us to the next question: Is neck turning your brass always beneficial, or are there some types of rifle and ammunition that won’t benefit from it?
The great thing about this particular question is that neck turning—done right—never hurts. If you want to leave no stone unturned, by all means try it. Candidly, though, production-grade hunting rifles right off the rack are unlikely to display a measurable increase in accuracy with neck-turned cases. Groups may or may not shrink, but is a drop from a 1.5-inch average to a 1.4-inch average worth the time and effort? Probably not.
A decision about whether or not to neck turn your cases should be based on two elements. These are the quality of your brass and the quality of your barrel and chamber.
Assuming you have a premium match-grade barrel correctly mounted and chambered to a trued-up action, neck turning your cases is worth a try. If you discover a measurable accuracy benefit, continue neck turning. If not, don’t bother.
Brass quality is a major determining factor. In my experience, only Lapua brass is so consistent that practical accuracy rarely benefits from neck turning. Norma and Nosler brass are also superb but can sometimes benefit from neck turning. Basically every other manufacturer’s brass exhibits significant neck-thickness differences and—if your barrel and chamber are accurate enough to realize the benefit—will improve by neck turning.
This last statement begins to answer the final question posed in the intro to this article. Specifically, whether benefit from neck turning can be predicted. The answer is yes, but not with 100 percent accuracy.
In essence, if you have a production-grade barrel with a production-grade chamber on a production-grade rifle, most likely you will see little improvement by using neck-turned brass. Quite simply, such rifles do not possess the accuracy needed to glean the benefit of neck turning.
On the other hand, if your rifle has been rebarreled with a match-grade tube and properly chambered with a min-spec reamer, you’re best served by either shooting expensive Lapua brass or lightly neck turned Nosler or Norma brass—or aggressively sorted and neck-turned brass from any of the big-box manufacturers.
There’s one final situation in which neck turning cases is almost mandatory. That’s when you’ve necked down a cartridge case significantly in size—for instance, if you were to create .260 Rem. cases out of .308 Win. cases. Compressing a case’s neck in diameter thickens the case walls, frequently to the point where the case will not chamber once a bullet is seated. Worse, the neck often thickens inconsistently. Turning the neck thins it to appropriate thickness and evens out inconsistencies.
To try to evaluate the effect of neck turning and put some sort of chartable indicator on its benefit, I recently handloaded dual 10-round batches of ammo—one neck turned and the other not—for two different rifles. The first is a Remington 700P LTR in .300 SAUM, a production-grade rifle but built with quality parts. The second is my much-loved Proof Research Summit in .280 Ackley Improved, a true match-grade custom mountain rifle.
Each lot of 10 cartridges was fired in five-shot strings, and I allowed the barrels to cool completely between groups. Each batch was then averaged.
Both loads were with new, untried projectiles in those rifles, but I figured that aside from the neck-turned cases all else was equal, making it a valid test. In retrospect, I made one mistake: I used Nosler cases for both rifles, and even the non-turned brass was pretty consistent. I should have used a lesser-quality brand that would provide greater distinction between the neck-turned cases and the original, as-is cases.
Another variable came into play. Both rifles are fit and sighted in with suppressors, and I fired the tests in cold, 35-degree temps. Heat waves off the suppressors caused significant distortion in the scope’s field of view. By the third shot in each five-shot string, mirage had the downrange target spots shimmering and blurring to the point that sight picture degenerated. All the groups displayed vertical stringing as a result. A couple of fliers that impacted significantly high or low were almost certainly victims of the mirage.
However, the groups fired from non-turned cases displayed a couple of horizontal fliers, and I’m comfortable attributing them to the less-consistent neck concentricity and tension.
The .280 AI displayed the most interesting results. With neck-turned cases it put four of five shots into an average of 0.68 inch—and all five into 0.81 inch—a difference of 16 percent I think was caused by barrel mirage.
Original, non-turned cases put four of five into an average of 0.59 inch, actually slightly better than the neck-turned cases but certainly within the realm of human error. More importantly, the five-shot-group average was 1.2 inches, a dramatic 52 percent increase caused by horizontal fliers. Presuming that those fliers were the result of less-consistent case necks, this particular rifle benefits from neck-turned cases. However, it’s such a small sample size that—obviously—additional testing is needed.
Predictably the Remington—with its factory-spec chamber—displayed less variation between handloads in neck-turned cases, which averaged 0.98 inch, and factory-original cases, which averaged 1.15 inches.