They stretch it out very carefully using a die.  But this isn't true of all wildcats.  If the size change is too extreme, stretching isn't an option and creating a new case is in order.

Sometimes a wildcater will cut a very long case at the shoulder and then neck that down to the desired size rather than necking UP another already shouldered case.


-T.

All the above is correct, of course.  It gets rather involved when you make radical changes, but in the case of .35 Whelen and the like a case is simply run over a tapered expander and the case neck opened up like one would resize a ring.

To neck down a case, the case is run into a die with a smaller neck.  You do this everytime you resize the neck when you reload, necking down is just more of the same.


When you neck up or down, you also thin or thicken the case neck slightly.  Most wildcat chambers take this into account.  If you were to try to make .22-250 cases from 30-06 this would need to be addressed.  Fortunately, 22-250 cases are easy to buy.  Necking down cases also makes them longer.  A radical example:


Factory cases are typically formed to be useful in the cartridge for which they are headstamped.  This isn't always the case, but 99%.  I've got cylindrical  brass from several manufacturers, but you mostly have to seek this out.

But then how do you ensure your franken-bullit will be safe to use?

Wildcats are cool.  I never thought I would get into wildcatting until one day I stumbled upon a beautiful Sako in 17-222.  This is a 222 Remington necked down to take a 17 caliber bullet.

My first time at the range I did a quick sight in at 50 yards then proceeded to set a pop can filled with water at the same distance.  I took a shot then went downrange to see the damage.  What I was looking for was a can with a small entrance hole and a large exit but what I found was a many small pieces of a can that had been destroyed by a 25 grain bullet moving at 3900 FPS.  That bullet must have completely grenaded.

Someday I need to try it on a prairie dog......

But then how do you ensure your franken-bullit will be safe to use?

  Are you talking about the rifle I'm having built?

Be assured that the guy building it is not named "Frank", and he's very good at what he does. The 1903 is a good action to build on for non-magnum applications, and Shilen barrels are a high quality product.

The big keys:

1. Having a safe action to build on(best determined by a good gunsmith with the proper equipment)

2. Having a correctly head spaced chamber.(Again gunsmith territory with the exception of Savage rifles with a barrel nut.)

3.  Your/my job?  Understanding powder burn rates, knowing how to watch for pressure signs, and knowing how to use a chrono during load development. 

And now I will take the liberty to clear up some issues that do not let me understand head spacing.

For example, in laymans terms, what does it mean that cartridge XYZ headspaces at the shoulder?

And then I remember hearing something about headspacing and gos and no-gos.

Headspace is the distance between the breech face of the gun and whatever is the first thing that a chambered cartridge bumps into. Ideally the cartridge will not quite completely fill that distance. Too little headspace and the action can't close. Too much headspace and you may run into problems such as the firing pin not reaching the primer or the case stretching excessively to fill the available space.

What part of the cartridge it is supposed to headspace on depends on the type of cartridge. Rimmed rounds generally headspace on the rim, straight walled rimless rounds generally headspace on the case mouth, belted rounds headspace on the forward edge of the belt, and rimless bottlenecked rounds typically headspace on the shoulder. There are some exceptions. .357 Sig headspaces on the case mouth, and it's common for handloaders of rimmed or belted bottleneck rounds to minimally resize their used brass so that it headspaces on the shoulder.

Headspace gauges are used when installing a barrel or cutting a chamber and for checking for safe headspace in a used gun. The gauges are machined steel tools that simulate the critical dimensions of a cartridge. A GO gauge is equal to the minimum length of a cartridge (from the base to the part on which it headspaces), the action must be able to close on the GO gauge or the headspace in too short. A NO-GO gauge is a bit more than the maximum length of a cartridge, the action of a new gun shouldn''t close on a NO-GO. A Field gauge is the absolute maximum length for safe headspace. It's for checking used guns and the action should never close on a field gauge, otherwise it's dangerous to shoot.

Clear as mud?

Jesse, can you perhaps put up some diagrams?

Then it will be clear as day.  I am one of those visual learning type of people.

THANK YOU.

Setting headspace involves the gunsmith carefully trimming material off the barrel threads and checking with a headspace gauge until the desired tolerance is reached.  That way a custom built gun can be set up with a super tight chamber in an attempt at a high degree of accuracy, or on the looser side for AK-like reliability.  Mass produced rifles usually split the difference.

That's one way to dot it, but depending on the particular action there are several other ways to set headspace too.

For some bolt actions, especially those that need to have the barrel installed at a particular angle due to things like extractor clearance cuts, the gunsmith may control headspace with how deep the finish reamer is run, rather than by cutting back the shoulder of the barrel.

In Lee Enfields, the headspace may be adjusted with different size bolt heads.

In Savage bolt actions, headspace is controlled by how far in the barrel is screwed. The barrel is then locked in place by a lock nut.

In M14 type rifles, a special pull through chamber reamer driven from the muzzle can be used in a short chambered barrel. Headspace is just right when the bolt closes.

Naw.  Just found them with Google.


-T.

Dang right. The last thing I need is someone mistaking me for an expert and taking what I say too seriously.

Mm.  I suppose it does.

After some thinking on it, the clue might be in the name.  "Field" might mean that when in the field, the only thing that really matters it sending lead down range without damaging yourself in the process.  When under fire, you want the maximum tolerance possible for the sake of speed in making the weapon ready to fight with.  The wider the margin for error the better, eh?  You want to goof with it as little as possible and get in the fight.

On the other hand, when in the shop or at the bench, you'll have the time to work on the tighter tolerance so as to not be so hard on your brass and the gun in general.

Just an educated guess.


-T.