How To Choose the Right Bushing for Your Neck-Sizing Die
One of the most commonly-asked questions on our Shooters Forum is “what diameter bushing should I use with my neck-sizing die?” While we recommend that users obtain at least two bushings, you still have to know where to start. For hunting ammo and gas guns, we still recommend choosing a bushing that is 2 or 3 thousandths smaller than the neck diameter of a loaded round. However, in a bolt-action benchrest gun, you may well get superior accuracy with less neck tension. A while back Larry Isenhour set a spectacular 50-5X, 600-yard IBS record using very light tension — Larry employed a .268″ bushing for a .2695″ loaded round.
How to Select the Right Neck Bushing for your Cartridge Brass:
A while back, we discussed neck bushings during a visit to the Redding Reloading booth at the NRA Annual Meeting. In the video above, Patrick Ryan of Redding explains how to measure your cartridge brass and select the proper bushing diameter. Please note that Redding has changed its recommendations for benchrest neck sizing in recent years. Redding now recommends that benchresters start with a bushing that yields slightly less grip on the bullet.
This is “right bushing” concept is very misleading.
First of all you will never end up with only one bushing, more importantly you should have more than one bushing.
You will actually need progressively smaller bushings as the brass work hardens after firing…. Easily 0.002” smaller than you started with over the life of the brass.
Furthermore… sizing down from a fired round in a standard chamber to a size that will hold a bullet, creates a taper to the neck with the mouth smaller than toward the shoulder.
To remove this taper, resize the neck one more time with a bushing 0.001” smaller than the first.
You might even repeat one more time with a 0.001″ smaller bushing to get the neck walls really parallel.
You can feel a change in the resistance when cycling the lever on your press and can feel when its right.
You will also feel the difference when seating bullets.
Just make sure you finish at the size you need that creates your desired neck tension.
Bushing sizing dies have many flaws that show up with competition sizing dies. Top competitors are going back to custom solid neck dies.
One more point about the correct bushing size…
As stated above, the brass hardens with each firing. As the brass hardens you get more spring back during neck resize and that eventually demands the next smaller bushing.
But what if you anneal the brass?
Well… Then you are back to square one and you should use the larger bushing again.
If after annealing you can achieve neck tension with a larger bushing than you initially used for new brass, interpret this as meaning your brass has been over annealed… or at least some of them were.
EDITOR: Yes changing bushings may be required. However, this need to switch may be over-emphasized. I shot a 6BR for many years with up to 8 firings between anneals with no need to change bushing and no loss of accuracy. Furthermore, after annealing, the originally-selected bushing still yielded the best accuracy. Going to one-size smaller bushing gave too much tension. While it involved a different system, I have had outstanding success with a honed FL-sizing die (no bushing), and again, there was no loss of accuracy even after repeated firings. That said, it’s certainly not a bad idea to have a bushing .001 less and .002 more than your current optimal bushing size — that gives you options. And if you find you have too much resistance to bullet seating (with your current bushing size), try leaving the carbon in the inside of the case neck after firings.
Interesting…
Am I correct in assuming that you had very little clearance in the neck of your 6BR bench rest rifle?
The amount of neck work hardening is relative to the amount of resizing required.
A reduction of 0.012″ per firing (like a factory chamber) will strain the brass much more than a tight neck chamber with brass that only needs to be reduced 0.002″-0.003″.
EDITOR: .003 Clearance with loaded brass in chamber.