These are widely considered a “step up” from a routine case sizing die. Well. Not always, or at least not in all ways. Lemmesplain.
First, a “bushing-style” sizing die is manufactured such that the user selects the desired bushing, and this allows control over case neck sizing. A good example is the Redding “S” die, and there are others.
By Glen Zediker
There are a few reasons neck bushing dies came about. Probably the main reason came from those who want to do away with the expander or sizing button. There’s a widely-held belief that an expander is a bad thing, that it contributes to non-concentric ammo. I disagree, with a couple of qualifications having been respected. One is that it’s been treated as I have said time and time again: polished and centered.
Anyone who has measured results from a conventional sizing die after the expander has been removed know that the case neck outside diameter is sized down way on smaller than needed to grip a bullet. That’s what the expander does coming back through the downsized neck: it opens it up to a workable diameter. The combination of the outside sizing and the inside sizing determine “case neck tension,” which is just the difference between the case neck diameters before and after bullet seating.
Here’s some math (and this is all about math): Let’s say loaded (with bullet) case neck outside diameter is 0.248 inches. If we want to attain 0.002 “tension” then sized case neck outside diameter needs to be 0.246. Although this varies with the alloy composition and the number of uses, every sizing operation done results in some amount of “spring back” from the brass. Brass is elastic. The most constant figure I can give is that this amount will be at least 0.001 inches. So. If we want a neck outside diameter to be 0.246 we need to use at the least a 0.245-size bushing. If a standard sizing die is reducing the neck outside to 0.240 (common enough), then it’s pretty clear the expander has a chore to open the neck back enough to net a 0.246 outside. That, pretty much, is the source of ills associated with expanders.
So. It looks like bushings are the answer. Well, not so simple as all that. There’s a few issues. The neck walls in a cartridge case get thicker after use and reuse. If there’s no expander to set the inside case neck diameter, then the inside case neck diameter is going to get smaller and smaller if only the outside of the neck is sized. Follow?
Another issue is that the neck bushing doesn’t or won’t size the full length of the case neck cylinder. There’s about a 0.020 area that doesn’t get touched. Whether that’s a problem or not depends on the bullet seating depth needed. Keeping in mind that there’s no expander functioning to open up the downsized neck cylinder, that little untouched area coincides with the location of the “dreaded donut” that can, and will, exist. This is a little elevated ring that lives right at the case neck, case shoulder junction. It’s daggone bad. More in another article. Upshot is that leaving this area untouched can contribute to its influence, and seating depth matters because if no portion of a bullet’s major diameter extends into this area, then it never factors. But most extend below it from a little to a lot.
If anyone chooses to use a bushing die, I strongly suggest that they still run an expander (or a mandrel as another step/station) in their sizing op. Inside sizing provides more consistent sizing results use to use to use than only outside sizing. If not, then there’s a lot to keep up with. Bushing size has to change as the necks get thicker, or the necks have to change, and that’s another two articles… Plus, some semi-autos leave ding-dents in the case mouth area, and an expander irons those out; outside-only sizing won’t.
I have a local machinist modify my conventional sizing dies by increasing the neck sizing area diameter. I get him to set a size that gives the expander 0.003 to displace. Mo math!
The preceding is a specially adapted excerpt from the new book Top-Grade Ammo, available for pre-order now at BuyZedikerBooks.com or ZedikerPublishing.com
.003 the average thickness of a human hair! “Mo math” indeed.
I do concur; however, that the rifle case neck is one of the areas that the brass flows to. Possible reason to not only outside neck “ream,” but inside as well. I think that necessity might only come after ‘several’ loadings and firings of the same case, unless you are one of those “one hole” shooters at 600 yds!
It might well be pointed out that by the time you experience any MAJOR issues in the neck area, your concern should be on the area from which that brass is coming – thinning the case just in front of the web – if the case comes apart, you might not enjoy the result!
Jamming the case in the chamber with a neck that has no room for expansion to release the bullet is a definite BOOM danger; however, again, by the time the brass has moved that much, the case is past the point of hitting the “recycle bin!”
I think there my be an exception to the new wall thickness changing or at least changing very slowly.
After doing some extensive reading about some of the methods bench rest shooters use for their rifles, I decided to try something that does wonders for case life. Or at least it appears to be true for me. What I read was about “tight necked chambers” and how many of them often get 100 reloads per case using a “tight necked chamber”.
I purchase 100 rounds of Lapua brass for my new Shilen “Select Match” .250″ diameter tight-necked chamber”. Brass was turned to a .012″ wall thickness giving a total of .002″ total clearance around the neck portion of the chamber. To date my necks haven’t increased in length more than .006″ & some less than .002″. I measure the neck wall thickness before reloading every time. The neck wall thickness of these 100 ea 22-250 cases has not changed. I assume this is because there isn’t enough room for it to grow in. I do know what they measure though.
Before anyone makes the assumption, I must not no know how to measure precisely. Rest assure, I do. I worked for 46 years measuring very close tolerances of .0001″. That’s 1/10,000 of an inch. If you could divide the thickness of a piece of copy paper into 40 equal thickness, one of them would be .0001″.
I haven’t lost a single piece of brass & expect I may never need to buy more brass if what I read is true about BR shooters & case life. Neck sizing with neck bushing is all I’ve ever done with these cases. These cases have been reloaded 7-8 timesThe only thing I have noticed, is a slight donut has formed at the junction of the angle where it meets the brass inside the case. But so far this hasn’t been a problem since the neck portion seems to be long enough to keep the base of the bullet away from the donut.
I agree. At the pressure levels I’m running for competition loads, my cases are done for prior to anything like excessive thickness. it always is wise to keep after it, though, because, over time, it can be a serious problem.
I always cam over about .003 just enough to feel it on bottle neck cases and never had a problem, also i found out many years ago that when reloading they will fit any rifle of the caliber you are reloading, been reloading since 1967 and about ready to give it up….
I neck size with bushings only for my 6br with lapua brass and my chamber is .272 no turn neck and have loaded some of this brass 20 times so far and have never trimed the brass and it hasent grown over .002 thousands and I load hornaday 57 grain v-max bullets with 8208xbr and run them out there at about 3750fps out of the barrel.Great prarie dog medicine.
I think neck sizing only with bushings is the way to go if you have a barely no turn neck or a tight neck like I have on my duce. I have a hart barell on that with a 246 neck so have to turn the brass again lapua brass to .011 thousands to have about .002 grip on the bullet. thanks for reading my comment. Rich Lee
I have been using Lee collet dies for years .Lee will grind the mandrel to any size you want no guess work there , size the brass then turn the outside of the necks
Sorry I’ve been neglecting responses… Been out for a spell. Keep in mind that this article and the advice in it is geared to someone loading for a semi-auto and also someone who wants to keep it more “simple.” For myself, yes, I do all the inside/outside case neck work. Point is that I think we’re buying into additional maintenance using things like bushing dies. That’s all good, if the reloader is willing to look after it. With some set-ups, like tight-necked rifles, all this extra work is accepted from the get go.
Great info. I have one question regarding the term “treated” when making reference to the expander ball. What exactly does that term mean ?