Fire forming wild cats

Discussion in 'Reloading' started by J E Custom, Jul 4, 2012.

  1. J E Custom

    J E Custom Well-Known Member

    Jul 29, 2004
    Having fire formed many wild cats I just had an interesting outcome and wondered how
    many of you have had this happen to them.

    Having read about the problems of the 22 hornet while fire forming I was ready to take on all
    problems but was not expecting the outcome I had.

    Before fire forming, I measured the case length to see how much growth in length I had to
    monitor case thinning.

    The cases did not lengthen but actually shrank in length by .009 thousandths.

    I can theorize why it happened but would like to hear what experiences anyone has had with
    this and how/why It happened.

    I am very happy with it, but it is the first time for me that a case has shortened while fire forming
    in a larger chamber .

    Any theories or comments are welcome (You are never to old to learn something).

  2. Edd

    Edd Well-Known Member

    Jan 26, 2011
    Without seeing the shape of the cases it's tough to comment. But I'd guess your case surface changed shape. Did the length of the surface get shorter or just the end to end length?

  3. Mikecr

    Mikecr Well-Known Member

    Aug 10, 2003
    If you improved shoulders, they pulled the neck back.
    I see this all the time.
  4. Trickymissfit

    Trickymissfit Well-Known Member

    Jun 11, 2010
    I've found in the past that when fire forming an improved case shape, that the over all length will shorten as much as .04" (usually in the neck area alone). Some cases are much worse about this than others, and I think it has to do with just how much brass is moving around during the fire form operation. My 30 Herretts shrink about .02" while my 6/250AI goes close to .045". I've heard guys that shoot the .243AI loosing .040" - .050" in neck length
  5. Boss Hoss

    Boss Hoss Well-Known Member

    Nov 10, 2005
    Very normal for improved cases---brass has to fill somewhere...
  6. Varmint Hunter

    Varmint Hunter Well-Known Member

    Dec 26, 2001
    Fire-forming 6mm cases to 6mmAI ALWAYS resulted in shortened cases. It never presented any problems though.
  7. specweldtom

    specweldtom Well-Known Member

    Jun 7, 2004
    JE, about 4 yrs ago, on every rebarrel and rechamber that I did, I started recording the dimensions of unfired rounds and then the dimensions of that same case after firing. I only have 8 examples.

    .375 H & H (belted) rechamber. case OAL unfired---- 2.840". Fired------ 2.854". SAAMI std. --- 2.850".

    .358 Norma Mag (belted) rechamber. case OAL unfired--- 2.505". Fired---2.500".--- std.(Barnes book)--2.520".

    .270 WSM rebarrel. case OAL unfired----- 2.094". Fired----2.097". ---- SAAMI ---- 2.100".

    7 x 57 Mauser rebarrel. case OAL unfired----2.238". --- Fired---2.240". SAAMI---2.235". (S&B ammo).

    6.5 x .284 Norma rebarrel. case OAL unfired---2.170". Fired---2.169". std (Cartridges of the World)---2.170".

    6.5 x .284 Norma rebarrel. case OAL unfired--2.160. Fired---2.160". std. 2.170"

    6mm BR Norma rebarrel. case OAL unfired----1.554". Fired----1.554". std. (Nosler book)--1.560".

    .22 Kilbourne Hornet rechamber from Hornet. case OAL unfired----1.4" (WW brass). Fired----1.395". Std. (Hornet), 1.403".


    One belted mag case OAL grew .014".-------One shrunk .005".

    Two factory rimless rounds grew .002" to .003".

    The two 6.5 x .284's shrunk .001" or less.

    The 6mm BR was unchanged.

    The K-Hornet shrunk .005".


    The fireformed K-Hornet approximates your experience. For the others, I would hate to have to predict what they will do, based on the very limited data I have, but it appears that standard factory rimless rounds stretch when fired the first time. Years of reloading support this because of all the times I've had to trim brass back after repeated reloading. That experience holds true for repeated reloading of belted magnums also, but they don't grow much before the primer pockets get loose. The only belted magnum I've had to routinely trim was a .300 H & H. It would get too long before the primer pockets loosened.

    Different brands of new brass and ammo were used, but since the dimensions were taken on the same hull before and after firing, the data should be accurate. In some cases, the std. dimension that I use may be a maximum case length.

    JE, I got way off your original subject, but the thread caused me to go back and see if I could make any sense out of what little data I had for several cartridges.

  8. J E Custom

    J E Custom Well-Known Member

    Jul 29, 2004
    Thanks to all that replied to this post and I hope more conversations are still coming.

    The reason I added this side note is that normally I make provisions for the neck to
    shoulder junction to be in the proper position of the wild cat chamber to head space on
    thus normally preventing case stretch.

    Fifty posted a great post on his approach to this problem with the K Hornet and I was prepared
    to use it if needed.

    This is the first Rimed cartrige that I have wildcat-ed and much like the belted cases have the
    full case length to contend with. I have made provisions to limit head space on all cases to be
    fire formed and just had not had this type of change.

    The Hornet is a low pressure cartrige and may be the biggest difference.

    It just goes to show "The rule is, There is no rule"

    Again thanks to all, and thanks to specweldtom for all the data.

    Interesting !

  9. Buttermilk

    Buttermilk Well-Known Member

    Dec 19, 2005
    On most improved cases, the shoulder of the case is increased in diameter and I believe this causes material to be pulled from the neck area resulting in a shorter case.

    All of my improved cases have exhibited a shortening after fireforming.

  10. Zep

    Zep Well-Known Member

    Dec 4, 2011
    J E Custom - I would like to hear your impression on the 22 K Hornet. Is it really worth the effort? I had been reading the basic 22 Hornet does not have to be maxed out powder/speed wise as many varmint loads do for best accuracy (maybe I am totally wrong). That makes me wonder it the K is worth the extra effort.

    Of course all comments are appreciated. Thought I would start here instead of posting a new thread.
  11. Brush4646

    Brush4646 Well-Known Member

    Apr 30, 2003
    Having fireformed thousands 0f PPC brass from 220 Russian it all ways shortens if you jam the bullet and lube the case so it doesn't grab the chamber walls.
  12. trueblue

    trueblue Well-Known Member

    Feb 18, 2008

  13. 41mag

    41mag Well-Known Member

    Feb 7, 2005
    In looking back over to the post of Fifty's you referred to, that is the method I use to form the cases for my Contender in 7x30 Waters.

    For the most part I simply use range brass as most don't reload the 30-30 and there is usually plenty of it to be found. I have found it almost completely eliminated any split cases that I had seen using other methods. Also as with Firty's results in accuracy I also see the same thing as well. The FF loads shoot just as tight as the final rounds.

    That is the only one I load for which has the rimmed case, that gets any real resizing when fired. With my 30-30 AI it's just the same however, if I run the cases through a .303 Brit sizer to expand the neck just a touch to give me the false shoulder, I get great results with them as well.

    Like has been mentioned in all of my AI chambered barrels and the Waters, I do see some shortening, but it hasn't effected much if anything IMO, as they all still function and group the loads just fine. Once formed I simply trim the mouths to square, and give them all a consistent lenght, and go on about my business.
  14. Clark

    Clark Well-Known Member

    Oct 19, 2006
    223 shrinks more, the more pressure in firing.

    And when FL resizing, grow more, the more it shrunk.

    And when FL resizing, grows more, the more the shoulder gets pushed back.

    To get .008" growth per cycle of firing and resizing, the shoulder must be pushed back .005".