I need some suggestions on case forming

[kbstenberg]

I have a problem forming 223 brass to 7TCU. I went through about 300 pieces of 223 brass looking for the longest cases I had. the shortest case I segregated was 1.754" the longest I had was 1.77".
I did a 1 step process running the 223 brass into my RCBS 7TCU sizing die. The trimmed length is supposed to be 1.75" for the TCU case. I lubed each case inside the neck before re-sizing.
The shortest of the resized cases was 1.73? and the longest was 1.74?.
is there a way when reforming to lessen case shrinkage? Kevin

[GRUMPA]

I do a lot of those, and if you don't use LC 5.56 brass your never going to achieve the length your after. Over time I've learned most of the other head stamps make things to work, and not so much precise. The way things are when you start out with 5.56/223 brass you need to find cases that are on the high of the case length. When forming into 7mm TCU the case shrinks, always will have that happen, that's why its important to work with a parent case that's at the high of the case length.

[Artful]

You want it longer, start with a longer case like 222 magnum then trim.

If your going to keep using 223
- don't clean/lube the inside of the case neck and rough up the expander it will pull the neck when you form the case - it to help but you won't gain much and it thins the neck.

In Theory, if you don't use the die to reform the case but fire formed the 223 case into the 7TCU chamber you would have the maximum effect on stretching the case forward at the same time as forming it. Maybe something to experiment with.



Here a swage die for the old black powder straight wall cases.


Another way
https://www.youtube.com/watch?v=oGzQsrPT4Qs
The only other thing I can think of is, if you have access to a lath you can stretch them.

If you’re fortunate to have a lathe or a friend that has one, brass can be
lengthened using a “nib & spin” technique.
The process involves the use of a die to hold the case and a “nibbing rod”.

The nibbing rod is similar to a boring rod but has a very smooth hardened bump on one side close to the end, or has a hardened ball bearing seated on one side to form the bump. A die, similar to a full-length resizing die, is constructed to rigidly
house the case and hold it from turning. The die inside diameter (ID) must
closely match the outside diameter (OD) of the case. The die and case are
aligned and clamped in the chuck jaws.

Once everything is setup, the nibbing rod is inserted deeply into the case at a point where the case wall is thicker. As the lathe is running the rod is adjusted so that the bump or ball bearing presses against the wall of the case and slowly “irons out”
(thinning) the wall as the case spins and the rod advances towards the
case mouth, hence the term “nib & spin”.

As the wall is thinned the excess brass is forced forward lengthening the case.

The photos below were provided by Mike Deland, aka mdeland.




The last photo displays the results of two lengthening runs of a .45-70 case.

An original .45-70 case is on the left for comparison.
As an example, from slightly less than 2.1”,
the long case on the right was lengthened to over 2.67”.


http://www.texas-mac.com/Stretching_...R_Chamber.html