Benchrest Central 

[an error occurred while processing this directive]

Tips, Tricks, & Info

| BC Home |    | Info Home |

  • Case Neck Turning and Annealing (Charles E.)

    The starting point is this: we want the bullet held as close to the bore centerline as possible. The easiest way to do this is to use a muzzleloader & be careful with seating the bullet. But since we want to use breachloaders, we need a different technique to get us to roughly the same point.

    Here's the sequence that's been worked out:

    (1) The neck portion of the chamber must be true (axially) to the bore.

    (2) The neck of the case must be "a close fit" to the chamber, so when the round is chambered, the bullet (which is held by the neck) is very close to the center of the bore.

    (3) The wall thickness of the case, at least in the neck area, must be the same.

    In other words, think backwards.

    If any one of these conditions isn't met, the other two don't matter too much. It's the old problem that if three variables matter, and you fix only one of them, the improvement to the system isn't much.

    So benchrest rifles approach the matter from the beginning, the cut of the chamber. The neck portion of the chamber is not only held true to the centerline of the bore (.0002 to .0004), but it is undersize from SAAMI specifications. A SAAMI maximum cartridge shouldn't even chamber. This forces you to turn the neck just to get the round to fit the chamber, and has the additional benefit of ensuring that the wall diameter of the case neck is the same.

    In short, you don't get much by neck turning if the other items haven't been done.

    Annealing is enjoying a rebirth. but remember for years, the best advise was "don't do it." The only reason I anneal is because I have to; I make small cases from big ones. The current popularity of annealing starts from the assumption that cases harden at different rates when fired & resized, so one should anneal to restore the evenness of the neck tension.

    There are a lot of assumptions buried here. First of all, benchresters don't use much neck tension, so a small variance in the elasticity of the brass can result in a reasonably large variance in bullet pull. If you use a lot of tension (high bullet pull) as is frequent in highpower, the small variation in brass hardness disappears into the noise.

    A second problem is that it isn't all that easy to do a good, even job of annealing, esp. using a propane torch. I use 700-degree tempilac, & still find that from time to time, I get one too hot, or another not quite hot enough. Red Ryder uses a steel plate with holes in it & heats the plate, which is likely to give much more even results. Torch work is a craft, & requires practice.

    Why does this matter? Because if your annealing isn't even, you are (at best) right back where you started, uneven neck tension. At worst, you've ruined the case.

    More than one old-time benchrest shooter wouldn't use a newly made case untill it had been fireformed a couple of times; obviously, their belief was that the work-hardening that comes from firing & the SMALL amount of resizing BR sorts do evened things up. By in large, this has been my experience. I did some chronograph work with just annealed cases and cases that had 10 firings through them. The Standard Deviation was better, by just a little, for the cases that had 10 firing on them. One could argue that the results would be different if I was a master annealer, and that may be true. But I stopped worrying about the need to anneal for "even neck tension."

    Updated: 12/19/99

  • | BC Home |    | Info Home |