Neck Sizing a Heavy Straight-wall Case to a Bottleneck

M

Mirage416

New member
Greetings fellow shooters,

I am building a new wildcat cartridge based on the needs of a local set of hunting restrictions that apply to me. In other words, it is out of necessity that I build the cartridge, and therefore the cartridge design is something which is maybe a bit of an oddball by the more common standards for wildcat cartridge designs.

In an effort not to ramble on about why I am using the parent case that I am using, etc, I will simply state the pertinent details. I'm hoping I can potentially get a little help towards obtaining a set of standards to follow, when taking a straight-wall case, shortening the case, and then bottlenecking it down. When I say, "a set of standards", an example would be, how much sizing to do per step (with each new die), I.E., Is there a ratio to follow based on case wall thickness, or diameter, so that I do not try to squeeze too much diameter down per sizing step? Another question would be, how many steps between annealing stages?

I am going from a case which is 0.635" OD and straight, down to about 0.330" neck, for .30 cal. So it's quite a large transition, which I don't expect to be easy to do without a proper process.

I am turning the dies myself from grade-5 bolts, since it machines quite well.

When making the neck sizing dies, are there any rules to follow about an entry cone shape/angle/size? Obviously I would make a shoulder bump die that gets run last, to create the final shoulder angle, I'm just wondering how I should properly prep for that angle bump during the neck sizing stages.

The neck is going to end up being very short, with a steep shoulder angle alpha of 45°.

I suppose my final question would be concerning prepping the brass wall thickness before neck and shoulder sizing; if I'm starting from brass which has been fire-formed straight, and I indicate off of the outside to ensure each case is centered, can I inside turn the brass thickness down past the entire shoulder to thin it a little in order to aid the sizing process? Or is that a no-no?

Sorry for all my questions. It's a new process for me, and I would just like to know that I will be setting the project up correctly from the start. Thanks for any help that any of you can offer.
 
Please NEVER be sorry for questions! "There Is Only ONE Dumb Question" :)

I do a lot of these and prefer not to go clear down from straightwall, instead trying to find a case that's within 30-40 thou.

I've recently premiered a bunch of case based on the .404 Jeffery for instance..... started with a .270 (which I made from 7MM RUM, squinched down) followed by .300 and .338 versions (which I blew up) during the course of these developments I tried 3 times to neck down from .404 and failed each time.

Necking down is hard...... IME you get ONE squeeze of maybe .020-.030 between annealings. I've done as much as .040 with NEW brass and home-aid dies. Different brands of brass yield different results.

I like Lapua
 
BTW several fellers on here have made and sold dies made specifically for this purpose..... maybe you'll get some real help :)
 
alinwa said:
BTW several fellers on here have made and sold dies made specifically for this purpose..... maybe you'll get some real help :)
Click to expand...

I think the largest neck down I've done was forming a 7MM Alpo from a 444 Marlin case. I used a 35 Rem, 308 and 280 Remington AI shortened. It was for a Contender and the 280 die was shortened so that a factory round wouldn't chamber. Skip Otto made form dies for such a project, but I believe mine came from PBIKE (Paul Becignuel, sp?). Paul's dad Francis reads this forum from time to time, but since he and Al don't quite gee haw, he make not look at this thread. I'll give him a head's up and maybe he'll post. I've used Paul's form dies to remake 6 BR brass (prairie dog) from well used 30 BR. Worked pretty well.

Rick
 
I used to make and sell case forming dies. I have reduced 458 Lott to 224. Needs to be in steps of .030. Don't worry about shoulder angle as your fireforming will take care of it.
 
wildcat

Mirage -

My custom RCBS case forming die set for my " .22-35 Remington " wildcat featured 3 neck-down steps.
.358" to .308" cal, .308" to .257" cal; and then .257" cal to .224" final cal. That's a .050" redux, followed by a .051"; and then a .033" redux.
That's how RCBS set up the forming die steps, and I did not do any annealing of the new parent brass efore performing the 3 neck-down steps.
The form set also included an inside neck ream die + reamer. My final desired neck wall thickness for the wildcat was .010", and I only had to do a veryminor amount of outside neck turn to uniform things.

Whenever / wherever possible, I like to do wildcat case forming using existing ( usually FL sizer ) dies. When this is the approach used, one would likley be utlilizing
dies for the more common calibres, and nothing exotic.

Thinking out load in loose terms.... an example neck-down process might be: .620" down to .585" cal, .585 - 550", .550 - .500", .500 - .452", .452 - 416", .416 - .366";
and likely then a final step of .366" cal down to final .308" calibre. While this last step is a neck-down of .058" ( more than the .050" redux proposed in previous steps );
let's remember that necking down brass several calibres can produce thickened case' neck walls. Therefore, reaching the final .308" cal desired for the wildcat will be a comination of both the final neck-down step + inside neck ream and outside neck turn; to insure final neck wall uiformity. The inside neck ream would be cutting the entire inside neck length. It would not be just cutting out a " doughnut ", especially on fore-shortened brass.

I'd have to research whether there are any existing dies that could work for your project, especailly whether there are any that could / would work if the die were shortened

I think of the final 2 inside neck ream and outside neck turn steps as insuring uniformity of the neck walls from a central inside reference point; as you are using mandrels. in the tooling.

Starting w/ new cases..... I'm not convinced you'd have to due any annealing. Once the shoulder location is set from the first step, and using a shoulder angle that allows for reasonable forming forces ( and no case losses ); then.... basically all the action will take place in the progressive calibre redux steps ( the neck ), along with some small transitions of material into upper shoulder surfaces associated w/ each calibre.

The final 45* shoulder angle would need to be fire formed, as such angles are too tight to be formed mechanically using traditional steel dies. A hydroform-type die might be a different matter ?


With regards,
357Mag
 
wildcat

Mirage _

Howdy, again !

As regrards case annealing:
You can always try form a trial case(s) using the dies chosen for the case forming process. IF / when you see any " striations " in the formed case' shoulders or even worse.... ones that go up into the neck wall; that'd be a pretty good indicator that the brass does need an annealing first.... and also possibly that the shoulder angle featured in the die(s) is too aggressive.


With regards,
357Mag
 
I would give RCBS a call.
You might even need to send them a drawing of the chamber.

They used to be very good at this.
They have a wide stock of dies that allows them to select multiple steps
to get the neck down bit by bit (or 'die by die').

It may require inside reaming or outside turning along the way.
 
Back again guys, this time hopefully with something useful that I can add to the discussion.

I was about to start turning a set of dies in order to keep moving forward with this project (which has a completion goal of being a chambered, complete rifle by October '23), and I thought about something; spin-forming. I've seen plenty of videos showing how various metals, including brass, are spun into highly different shapes than they started out as. Now, I'm no metallurgist, but an idea had been planted and I had to give that idea a try for myself--especially since the cost to try it would only be a few brass cases or so.

I had a pair of garage door rollers (or "wheels") in the package new with 7/16" axles. The roller radius looked like it would not work the object being spun too sharply, but rather give a nice gradual forming as it was fed down the spinning brass case.

Here's what I did:

•Mounted the garage door roller axle vertically in the chuck of the rotary table mounted on my Bridgeport bed.
•Used a 5/8" ER40 collet (the driven component in the mill) to grip a straight-wall 505 Gibbs case (case shortened to near the original shoulder location). Upon collet tightening, the Gibbs brass centered very well without requiring any indicating to rid wobble during spinning.
•Applied a little STP oil treatment as some lube on the case exterior.
•Chose 2000rpm as my guesstimate speed at my first-attempt case spin forming.
•Spun the case up, then slowly fed the roller up against it until it matched spinning surface speed, then fed another 40/1000ths or so until I clearly spotted deformation of the brass and a groove forming at the starting location.
•Pressed the button and auto-fed the roller towards the case mouth at a rate of about 20"/min.
•After each pass, repeated the same general operations of movement--though I was not ensuring each pass closed the case another I.E. 40/1000". Rather, I just wanted to see additional closing occurring to examine the end result.
•Once considerable shape change occurred of the case, I removed the case and examined what occurred.

Now let's get to the photos.

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I must now say that over the course of trying this on a single case, I developed very high hopes for using this process to quickly neck down a wildcat in which full-length sizing dies are lacked. But I won't be too naive, as it would seem that if this could take a virgin straight-wall case right to the process of fire-forming without a single die in the process, I'd have seen it somehow, somewhere, being used to do just that. I haven't seen it applied to rifle brass, however. That causes me to believe there's a reason.

I'm really hoping someone could maybe explain why this isn't (or is) being used for this task. Will the brass life be tremendously shortened? That's the only reason I can think of due to the work hardening occurring.

I figured I could go on attempting to perfect the process for my needs, or even proclaim that's it's surely a way to run the steepest shoulder angle without worry of shoulder crushing ever again, but I figured I would wait for someone who may point out some reasons spin forming isn't used, at least before ruining expensive cases I have finite supply of. If no one dissuades me though, then I will continue on perfecting what I can of the process for my needs and hope for the best.

Thanks for any further insight on this method.
 
I saw a video some years back where wildcats were being formed by chucking the case in a drill press holder and driving the neck into a chamfered hole of suitable diameter. This allowed for some dramatic reductions. I played with it a little, with no real need, and in a few short experiments it seemed to work. Pretty much just another take on what you've done there, although it might help get your shoulder closer to it's final dimension.

Good luck!

GsT
 
Just an observation. The resulting shoulder in the last picture resembles a Weatherby case.
 
GeneT said:
I saw a video some years back where wildcats were being formed by chucking the case in a drill press holder and driving the neck into a chamfered hole of suitable diameter. This allowed for some dramatic reductions. I played with it a little, with no real need, and in a few short experiments it seemed to work. Pretty much just another take on what you've done there, although it might help get your shoulder closer to it's final dimension.

Good luck!

GsT
Click to expand...

Just out of curiosity, did the form die against the case spin with it?

Because I would not think spinning the brass against something static would be very good at preserving the case surface; would think it would get all galled up.

So far I'm still fairly impressed with this method. I mean subtracting 7 dies from a process is kind of a big deal to me. ;) What I'm concerned about will be the life-span of the brass neck region after doing it this way. Though, it's hard to say with certainty which method is truly beneficial to the brass. The conventional method forms the brass axially (around the whole circumference at once, and starting from the front). Spin-forming acts on one small area of the brass, radially changing it's shape gradually, and begins at the shoulder--pulling the metal forward in the direction it needs to move to change shape.

Cases do crush with high amounts of conventional die forming/swaging, and I suppose in my lamens terms of attempting to explain why, it's because the brass is being compressed inward/downward, yet it still needs to actually move forward (gaining length). We call it "swaging", but it's being jammed into shape all at once around the circumference. There are large moments of force acting on distinct areas of the case differently, with swaging. With spin-forming, the pressure to change the case shape is rather constant and continuous, with the brass enduring similar forming pressure across the surface.

Is it that cut and dry? Surely not, but just how I am imagining the process momentarily. It will definitely take some time before I discover the pros and cons of the method within my own environment. I'll need to document my process as it goes along to develop a repeatable method to follow each time, in order for the cases to experience similar forming conditions each run.
 
Mirage416 said:
Just out of curiosity, did the form die against the case spin with it?

Because I would not think spinning the brass against something static would be very good at preserving the case surface; would think it would get all galled up.

So far I'm still fairly impressed with this method. I mean subtracting 7 dies from a process is kind of a big deal to me. ;) What I'm concerned about will be the life-span of the brass neck region after doing it this way. Though, it's hard to say with certainty which method is truly beneficial to the brass. The conventional method forms the brass axially (around the whole circumference at once, and starting from the front). Spin-forming acts on one small area of the brass, radially changing it's shape gradually, and begins at the shoulder--pulling the metal forward in the direction it needs to move to change shape.

Cases do crush with high amounts of conventional die forming/swaging, and I suppose in my lamens terms of attempting to explain why, it's because the brass is being compressed inward/downward, yet it still needs to actually move forward (gaining length). We call it "swaging", but it's being jammed into shape all at once around the circumference. There are large moments of force acting on distinct areas of the case differently, with swaging. With spin-forming, the pressure to change the case shape is rather constant and continuous, with the brass enduring similar forming pressure across the surface.

Is it that cut and dry? Surely not, but just how I am imagining the process momentarily. It will definitely take some time before I discover the pros and cons of the method within my own environment. I'll need to document my process as it goes along to develop a repeatable method to follow each time, in order for the cases to experience similar forming conditions each run.
Click to expand...

The die was static - just a plate with chamfered holes. Lube was used, of course. They may have taken the holes in steps, I don't really recall, but the whole affair was distinctly crude. I would definitely anneal after neck forming if case life is at all a concern (using either method). Having done so should eliminate concerns about shortened case life.

GsT
 
With our case forming die, the case neck is reduced in diameter with the use of progressively smaller neck buttons. There is no more case annealing needed than the regular annealling after a number of firings and really with tight neck chamber very little annealing is needed as the brass isn’t worked very much.
 
FBecigneul said:
With our case forming die, the case neck is reduced in diameter with the use of progressively smaller neck buttons. There is no more case annealing needed than the regular annealling after a number of firings and really with tight neck chamber very little annealing is needed as the brass isn’t worked very much.
Click to expand...

I was going to post a pic of my case forming dies and a photo of my 458 Lott brass necked to 224 size in a 1.5" oal length cartridge. I guess I'm not able to post photos anymore.
 
Butch Lambert said:
I was going to post a pic of my case forming dies and a photo of my 458 Lott brass necked to 224 size in a 1.5" oal length cartridge. I guess I'm not able to post photos anymore.
Click to expand...


If you guys are looking for a way to host photos, download the Imgur app or use their website. It's almost as quick as old fashioned free photo hosting sites. After I upload and submit images, you'll get a page with the photos. I click the photo on the page, and copy the link directly to the photo web location. Then you'll get the correct site address to use the "
" tags around in your post and they will show in the post like my images.
 
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