How can I resize the brass before using an expanding mandrel?

[JFrank]

This seems to be a tireless topic that’s worthy of discussing again.

Neck expander mandrels

I load on a Forster Co-Ax and am currently using Redding Bushing Competition Neck Dies on all my precision calibers. I currently measure the outside diameter of a loaded round and subtract 0.002” for the bushing dimension. Would there be any advantage to using expander mandrels 0.002” below...

www.thehighroad.org

 

[BBarn]

The ball doesn’t fully support the neck, so as you push the ball fully to the bottom of the neck, the top is allowed to contract above the ball in natural springback, so when you withdraw the ball, you’re still pulling up on the shoulder - without any kind of case support - and redrawing the diameter of the neck during the pull stroke.

Think about pulling an egg out of a snake vs pulling a post. The egg has to force elastic expansion as it is drawing out PLUS the friction of the wall, whereas the post only fights the friction. One is reshaping the snake along the way, one is not.

I wasn't implying that the approach was equivalent to using a mandrel. But it does seem to reduce the effort required to pull the expander out, and it can be done with standard dies. So there may be some benefit over the normal size and expand in one step with standard dies. Easy to try with no additional investment, especially for someone not on a quest for benchrest records and wanting to save money.

 

[Varminterror]

it does seem to reduce the effort required to pull the expander out

This reduction in resistance is because you have unwittingly lowered your case mouth out of the die neck, so your case is free floating without support within the die as the ball finds its way through the neck. By design and intension, the case mouth should still be supported by the neck of the sizing die at the moment the top of the ball contacts the bottom of the neck as you withdraw the case from the die. By sinking your stem and ball deeper, you eliminate that case support.

 

[BBarn]

No. Nevermind.

 

[Varminterror]

No. Nevermind.

My point was rather that while it SEEMS like hanging the expander ball low in the die and expanding separately would be relatively mimicking a mandrel expander, it really doesn’t pan out that way, and in fact, systemically is less likely to produce better ammo than using the die as described in its instructions. No free lunches to be had there.

And WHY do I know this? Because I tried the same idea ~22-23yrs ago when I was a broke student trying to take on long range reloading on a budget and thought I had discovered a trick to avoid the cost of the die. My concentricity went sideways, and I couldn’t figure out why… so I called my mentor, and IMMEDIATELY he pointed out exactly what I described above. I guess I should have asked if it would work before I tried it - or at least thought deeply enough about what I was really doing, because once he said it, it was totally obvious that I should have thought about the lost neck support for the die. “Ask and learn” is a much faster and efficient process than “Live and Learn.”

 

[westernrover]

Or "buy and learn." This thread has been tremendously helpful to me. For what it's worth, I'm ordering dies today and I'll get the Redding Type-S bushing die and a SAC bushing that should put the brass 3 under. That's exactly what I've done before with other cartridges. The dilemma that remains is whether I should leave the necks 3 under with a bushing-only OD sizing, pull my carbide expander ball through them (already have this caliber), or get a mandrel and push it through the necks.

If I were to get standard mandrels (Wilson, Sinclair, K&M, 21st Century) they are sized 1 under. According to what I've read in Accurate Shooter bulletins and other sources, the brass (typically Lapua) is expected to spring-back to 2 under, and it is advised to use 21st Century mandrels in half-thou increments if something else is desired or needed. I'm skeptical and I doubt my brass will spring-back. I believe if I push a 1 thou under mandrel through it, it will be 1 thou under and I'm doubtful that is enough neck hold. I could buy the 21st Century mandrel kit and have everything just in case.

If I were to do bushing-only sizing, the thing that concerns me is the obvious taper of my necks. Pushing a cylindrical bushing over a conical neck could do some bad things to the ID. I would feel more confident finishing by pushing a mandrel through or pulling a ball through to be sure the ID is cylindrical.

If I get a mandrel, it will probably have to be one of the 21st Century that is at least 2 thou under, and that will be a separate order. The only mandrel I can get on my die/bushing/bullet/wilson-seater order is a Wilson mandrel.

 

[JFrank]

Wilson bushings are tapered also bushings in general won’t size the entire neck to the neck shoulder junction, nor do they really need to.

 

[Walkalong]

The dilemma that remains is whether I should leave the necks 3 under with a bushing-only OD sizing, pull my carbide expander ball through them (already have this caliber), or get a mandrel and push it through the necks.

I pick a bushing so that the mandrel does at least a tiny bit of work on every single case, but no more.

Wilson bushings are tapered also bushings in general won’t size the entire neck to the neck shoulder junction, nor do they really need to.

The SAC bushings have two diameters, they gently take the case mouth down after it is surrounded/supported by the first part of the bushing. It really does do a better job. Concentricity will improve, especially if you are having to take the diameter down a good bit.

I have Wilson steel, Redding nitrided, RCBS coated, Forster, a couple of old Whitetail Engineering carbide bushings, and the SAC bushings are superior.

 

[westernrover]

I found the same thing with SAC bushings. I'm a total convert - previously I've only ever used Redding nitrided, but had problems when taking the diameter down too far in a single step. I haven't proved the SAC bushings are better with a fully controlled experiment, but what I have demonstrated to myself is that I get an OD that matches the printing on the bushing. With Redding bushings, I would get OD's less than the printed dimension. Yes, less. Can't explain it, but Redding acknowledges it happens. It makes it super frustrating to guess which bushing I need.

 

[Varminterror]

I pick a bushing so that the mandrel does at least a tiny bit of work on every single case, but no more.

This.

 

[JFrank]

I pick a bushing so that the mandrel does at least a tiny bit of work on every single case, but no more.

The SAC bushings have two diameters, they gently take the case mouth down after it is surrounded/supported by the first part of the bushing. It really does do a better job. Concentricity will improve, especially if you are having to take the diameter down a good bit.

I have Wilson steel, Redding nitrided, RCBS coated, Forster, a couple of old Whitetail Engineering carbide bushings, and the SAC bushings are superior.

I can’t speak for or against short action custom bushing’s, I hear they aren’t cheap but have never seen a side by side comparison or any results on paper that suggest they are any better or worse than another brand. I suppose It’s just up to the individual to decide so if something instills confidence than by all means use it.

Just my nickel’s worth…

 

[JFrank]

I wouldn’t mind hearing more about this two step process, are they tapered or have a step inside?

IThe SAC bushings have two diameters, they gently take the case mouth down after it is surrounded/supported by the first part of the bushing.

 

[westernrover]

I would describe them as having the first 2mm tapered. The Redding have a larger chamfer on the face of the bushing but no taper inside. SAC are less costly than Redding's bushings.

 

[JFrank]

I would describe them as having the first 2mm tapered. The Redding have a larger chamfer on the face of the bushing but no taper inside. SAC are less costly than Redding's bushings.

Thanks, if that’s the case then they must not size all the way to the NSJ ?

 

[Walkalong]

IThe SAC bushings have two diameters, they gently take the case mouth down after it is surrounded/supported by the first part of the bushing.

Correct.

Thanks, if that’s the case then they must not size all the way to the NSJ ?

Correct.


Chamfered, a slight taper from one diameter to the next, but two diameters.

This case was sized with a .264 bushing, and expanded with a .241 mandrel.

The top 80% or so is .266 OD. The .267 bushing is slid down over the case
neck in both directions. Near the bottom it tapers to .273. Most of the neck
is sized/expanded to the smaller diameter.

 

[JFrank]

So about a .001 taper, kinda like getting two bushings for the price.
I think Wilson is about half that taper which for myself is not a problem.

 

[Walkalong]

It does a better job than the Wilson, it really does. I'll go get my pin gauges and get some numbers.

I have done this already, but don't remember the numbers for sure, want to get it right.

 

[JFrank]

No worries, I’ll take your word for it.

 

[Walkalong]

The pins are warming up to room temp, came in from the cold.

I checked them when they were still cold, so it will be interesting to see if the one that would pass all the way cold (50s) through still will (72)


Edit:

OK, using my SAC .264 bushing, the .264 pin gauge will slip all the way through, while the .265 pin gauge will slip halfway in, from the bottom of course..