In an earlier journal entry I mentioned neck turning brass as a possible way to improve accuracy.
“Neck turning” consists of shaving the outer diameter of brass case necks to minimize variations in thickness. By uniforming the brass you’re supposed to get consistent neck tension, therefore consistent velocity and better accuracy.
A lot of smart people swear by it, but I couldn’t find much in the way of hard evidence for or against.
While chasing this down I also noticed people arguing that uniform primer flash holes were important. Again, while there were no shortage of opinions, I couldn’t find a lot of evidence to either support or debunk the practice.
The logic “in favor” in both cases was certainly convincing–particularly where run-of-the-mill brass is concerned–so of course I decided to give it a try.
But I also wanted to know whether it was actually worth the trouble, or if it fell in the category of “do it because it makes you feel better.”
I decided to run the test in a regular gun: in this case a .223 Wylde AR15 build. No benchrest machine or even precision bolt action rifle, but a step up from your generic gas gun blaster.
For my test I collected three boxes of recently fired U.S. factory “Brand X” .223 brass, cleaned and deprimed. I “shuffled” the brass and divided it into four groups of 15 rounds each:
Group 1: my usual brass prep
Group 2: my usual prep, plus uniformed primer flash holes
Group 3: my usual prep, plus neck turned brass
Group 4: my usual prep, plus uniformed primer flash holes AND neck turned brass
For Groups 3 and 4 I used an RCBS Hand Case Neck Turner with a .22 caliber pilot, although instead of the handle that came in the kit I used a large drill chuck to hold the brass cases.
(note: some of these are Amazon affiliate links, which means that if you click the link and buy the associated product, Amazon pays me a fee–your cost is unaffected)
I measured about half of the case necks with an RCBS ball micrometer and found that they varied between .0112 and .0127″ in thickness.
One option was to thin all the necks down to match the thinnest spot on any of the brass; that seemed a little extreme to me so I chose instead to just knock down the high spots to .0120″.
This would reduce variation in the case necks to less than .001″, which this ballistic tech from Sierra Bullets says is the goal.
Note: it’s important that your brass is a tight fit on the neck turner pilot to get consistent results: luckily for me, the brass came off my Sinclair expander die exactly the right size.
I used an .080″ K&M tool to uniform the primer flash holes.
For the test I selected bullets, primers, and powder that were already sitting on my reloading bench. While this particular load is no world-beater in this barrel, I expected solid enough performance to allow any trends to reveal themselves.
I loaded the four groups and noted the runout of each round on the Sinclair/RCBS gauge I mentioned in an earlier post. Groups 3 and 4 (the neck turned brass) showed slightly less runout, but all four Groups were below my cutoff of .004″ (for gas guns).
(I’d chosen .004″ of runout as a cutoff because with more than that I started seeing negative effects on target)
The next challenge was overcoming my own bias while shooting: while I didn’t really expect to see a big difference in accuracy between the groups, I was secretly rooting for Group 4 (uniformed primer flash holes and neck turned brass) to shoot better after all that trouble.
While I’d like to think I can be totally objective when the occasion demands, I realized it would be better to eliminate even the hint of favoritism, conscious or otherwise.
So I loaded each group of 15 rounds into a separate magazine, labeled with a yellow sticky. I then turned the magazines over to a truly neutral party–the whole business bored her nearly to tears–who shuffled them, randomly marked each magazine with “A,” “B,” “C,” or “D,” marked the yellow stickies with the corresponding letter, then removed the stickies for safekeeping.
I would then shoot three 5-round groups, round robin, from each magazine. I’d chronograph each group and take pictures of the targets, then, when I got home, perform the big reveal–reclaim the yellow stickies and match the performance of each magazine with its particular brass prep.
I went to the range and shot the test as described above. I was seated and supported the rifle on a Caldwell rest.
Groups 2 and 4 basically tied for best overall accuracy, both hovering around 1 MOA. Group 2 was more consistent, whereas during the final round of Group 4 I shot four into the same cloverleaf before I choked and sent the last bullet an inch wide and right.
Group 1 (my usual brass prep) and Group 3 (neck turning only) yielded only mediocre accuracy.
The chronograph readings were inconclusive as well. I think the small sample size may have hurt us here: if there WERE any subtle trends to tease out, 15 shots per group just might not have been enough.
Average muzzle velocity was consistent across the board at about 2,660 fps, with overall standard deviations also holding fairly steady between groups. Group 3 (neck turned only) did show good runout and slightly more consistent velocity, but that wasn’t reflected on target.
My conclusions?
- It may have been coincidence, but the two groups with uniformed primer flash holes ended up being slightly more accurate than the ones without
You only need to do it once, it’s quick and easy, so I think I’ll continue.
Remember: some brass–like my 6mm ARC and 6.5 CM–has small primer flash holes (.062″ vs .080″). If you’re going to load those you’ll need a different uniforming tool or at least a different cutter.
- I may not have neck turned aggressively enough to make a difference
- At least I didn’t hurt anything
There is more than one way to neck turn brass. While I’m pleased that I didn’t actually destroy mine, it’s possible that I might have gotten more dramatic results by completely trimming all the necks down to some baseline minimum rather than settling for a more moderate approach.
However, most of my sources (like this one) say no, just trim enough to knock down the high spots to within .001″. I’m still comfortable with that decision.
And at last, The Bottom Line:
- My testing doesn’t justify neck turning .223 brass for my AR15
I saw no clear evidence to support the practice with this rifle, either on target or on the chronograph.
Lots of caveats here, obviously: small sample size, undistinguished load, ditto shooter…
However, I DID see a decent group out of Group 4 at the end there (if you’ll allow me the cursed flyer).
Superstition, not science, therefore compels me to continue neck turning–at least the brass that stands to benefit from it most.