I know it sounds simple but I'm having a time fireforming some 223 cases. I measure them before and after firing (head to shoulder) and they don't change. I need to lengthen them about .004" to fit my rifle snug on closing.
I've tried partial sizing, neck sizing, always checking each case for center of shoulder to base with a die I made on the lathe.
What do you use for slightly shorter cases.
David

Why?

I believe that if you are neck sizeing brass fired in your rifle, that is as close as you can get. Remember the case expands and contracts a tiny bit in the fireing process.

Someone will jump in here if I'm wrong.

Guys I'm sorry, I should have put this in the reloading section. Thought I was there.
David

Everybody(well, most) make a big production out of fireforming, just make the first fireing a good stout load and the cases will form nicely, and in my experience are quite accurate on the first firing, go kill something other than paper and don't worry about a few thousanths in length for a while as long as they chamber without effort.
Stepchild

I suspect you are defeating yourself.

In a full power load, the case "blows forward"/shortens under primer pressure, THEN it blows back and the "lengthening" is dependent on how quickly pressure has risen and how firmly the neck and shoulder area has expanded against the chamber gripping it.

If you are fire forming with cream of wheat then forget this ....

And this is the reason they recommend not using cases that have been used for reduced loads/cast bullets with full loads... Might pull apart. Primer induced shortening not compensated for.

Then there was the scheme to lengthen the case by oiling it and firing a full pressure load so neck would not grip chamber... (Risky???)

Fire a full power factory or equiv load and hit it with a length guage. If too long, trim it. If not, reload and enjoy... Sure, your gauge will give you body info but don't over interpret and harm your cause... Luck.

David,
If the die is homemade, would suspect that a critical dimension was blown somewhere.
Personally, have had very good succes by VERY SLIGHTLY crimping 1st-time wildcats/reloads w/ a pair of smooth jaw pliers. Annealing the neck also helps. The idea is to provide JUST ENOUGH friction on the chamber's wall to hold the cartridge firmly against the breech face. I will carefully & very slightly squeeze the case @ approx 1/2 way between base & shoulder, then check it by chambering. Repeat if necessary. Slight friction upon closing is all we need.

I've formed 7mm TCU's this way for years & have had very few failures. As always, YMMV.

G' luck !!

1. Get a tapered expander that will open the necks up a few calibers, say from .224 to .243. These should be available from RCBS or Redding, also they should be available for expanding necks to .264". Lube the inside of the necks and run them over the expander. Back out your full length die several turns and lube the cases with something like Hornady's Unique Case Lube, avoid sloping on the shoulder area or you'll make dents. Size a case and try to chamber it. It won't fit, the bolt won't close. Don't force the bolt. Lower the FL die a 1/8th turn and try again. Repeat this until the bolt just closes with a bit of "feel." You now have a case with a slight double shoulder. Lock down the FL die. Load with a fairly stout load but stay under maximum. You need a stout load to overcome case stiction to the chamber walls, otherwise the case will shorten, check the primer - it must be flush with the case head, not protruding. Now you have minimal dimension cases that can be neck sized. Cases may need annealing after work hardening so much, but you should get at least 10 reloads before they need it.

2. Just try a few, if there is no accuracy improvement, then discontinue the practice.

There are some great ideas here. I am going over my procedure. What happened I found some cases way short and have been trying to figure out what happened. One thing I've learned, something I hadn't thought of was that a 1/8 turn of the die is .008". This could be part of my problem, sloppy on the setup. Also I have several presses and try to keep the same set of dies with a certain press, thinking back I may have used the wrong one.
Guys thanks for the help on this I appreciate it.
David

David,

I encourage you to try Wrangler John's approach above.

quote:

Load with a fairly stout load but stay under maximum

Also, as you're trying the above seat a coupla .224" 55 grainers out INTO the rifling with @ 95% load.

That ought to give you about as perfectly formed case as you're gonna get in your chamber.