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Thread: 7mm TCU brass not forming from a .223

  1. #1
    Boolit Bub beng's Avatar
    Join Date
    Jun 2009
    Lat. 33N 6' 48" Long. -84 15" 11" Middle Georgia

    7mm TCU brass not forming from a .223

    Have a quick question about 7mm brass.....I just got the TC 7mm TCU 10" pistol. Having trouble making the brass. Tried using the 7mm TCU dies and about 1/2 of all made will not fire form. Meaning the primer will not go off, it has a small dent in the primer pocket and at times the brass is INSIDE of the Extractor........ I got a new one (extractor) but the same. Do not want to put a .223 down the barrel.....So what do I do???????? Thanks for your time

  2. #2
    Boolit Buddy 35isit's Avatar
    Join Date
    Dec 2009
    Central Ky
    Your headspace is incorrect. If you are using minimum charge to fireform you can seat bullet until it just touches the lands. This will be the case against the breech and allow the gun to fire. There is a great how to on the specialty pistols forum. Bellm has a how to on his website. I set my die up to give a two to three thousands headspace when I make brass. I leave it that way and always size my brass the same.
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  3. #3
    Boolit Buddy
    Join Date
    Jun 2011
    Oklahoma / Wyoming
    My wife and I both shoot the 7mm TCU, mine a Super 14" and here is a 21" carbine.

    We use 204 Ruger brass in both guns, as it allows for an additional .100 case neck length after trimming and fireforming.

    All fireform loads are with a 160 gr. bullet jammed hard into the rifling, using book listed "middle" loads.

    Never had a round fail to fire and fully form, but when you do fireform, make sure your load is enough to fully form the shoulder. If it is slightly rounded, increase your powder charge accordingly, until you do get a fully formed shoulder angle.

    Only after the cases have been fireformed, do you need to trim the cases to length, but more importantly, to square the case mouth, because they can become quite distorted from sizing and the first firing.

    If you stay with 223 brass, you will wear your cases out from shooting them, before you will ever have to trim the cases again.

    When sizing, best accuracy with no misfires ever, comes from NOT full length resizing the cases. If you can feel just the slightest resistance when closing the action on a sized case, you should be good to go.

    Best powders we have found are H-4895, H-322 and H-335. CCI-450 is our first choice in primers, BUT when the outside temperature hits 90 degrees or higher, we then use CCI-400 primers. Of course ALL loads were worked up and tested, so we both know what loads our guns like best.

  4. #4
    Boolit Master
    Join Date
    Feb 2007
    Communism closing in!
    +10 on everything discussed so far.

    I would suggest newer brass that has not age hardened or anneal, then size up your necks as gradually as you can to avoid case mouth splits (stepped mouth sizing).

    As written above, use the bullet engaging the rifling to keep the case head against the breach face of your pistol.

    You can tell with a Contender if you have too little headspace because the gun will not fire, only click. You need to either seat your bullet a bit deeper or set your full length die ever so little deeper to increase the headspace by a small amount.

    Once you get it right, it is a very rewarding cartridge. I have a Super 14” and a 21” carbine barrel. They are both tack drivers with the right load.


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  5. #5
    Boolit Master marshall623's Avatar
    Join Date
    Jan 2011
    I usually take the barrel off the frame when setting up my sizing die and do a plunk test , I set my dies to where the case head is flush with the end of the barrel . That meathod is what a gun smith showed me as I was having alot of misfires with the light primer strikes . This is a little harder to do with the spring loaded extractor's for the 223 head family . You can tell if its going to act up when you cock the hammer , you look at the little transfer bar in front of the hammer as you cock it . When the gun is locked up properly you should see the transfer bar drop about a 1/16" or just see it move .If its not locked up, the bar will not move thus giving you the light strike . I thought I had my 30 Herrett dies set , I had some misfires at a match and then had it do it on a deer . I got the barrel out last week and re plunked them , had a few that were a little high instead of flush . I moved my die down about 1/32 of a turn and that looks like it fixed it .
    Good Luck , Tim

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  6. #6
    Boolit Master 243winxb's Avatar
    Join Date
    Aug 2005
    If the shell holder is contacting the bottom of the fl sizing die, you have pushed the shoulder of the brass to far back.

    Size just enough so brass will chamber & allow the action to close.

    I made the same mistake. If i remember correctly, dies were T/C brand years ago.

    Lots of split neck . Try annealing brass first.
    Last edited by 243winxb; 05-30-2020 at 11:56 AM.

  7. #7
    Boolit Buddy
    Join Date
    Oct 2008
    Colorado Springs
    In forming brass for the 7MM TCU I start with a .257 die and then later the 7 MM TCU. I lose maybe one case in 50 that way. Use lots, but not too much lube. I shoot all loads in my Contender with 14 inch barrel or my Savage Axis re barreled with a Shilen Barrel. My gunsmith had me bring in a cases so he could set the barrel on the Savage so ammo can be fired in either. 5.2 grains Unique behind 120 grain cast Old Lyman mold is great. dd

  8. #8
    Boolit Master
    Join Date
    Jul 2015
    Just to be sure, compare the location of the shoulder on rounds that did fire as compared to your 223 brass that you want to convert.

    If the shoulder on your fired brass is farther forward, you will need to do something to reliably get rounds to go off for fireforming.

    You may be able to seat your bullets into the lands, but you may have trouble with this solution. The throat on my 10" TC 7 Tcu is so deep, this method would not work with any bullet I have ever used.

    Another choice is trying to get the rounds to headspace off of the extractor and/or case taper. This gets more iffy the looser your loaded rounds fit in the chamber. You might want to try converting some 223 as follows. Take the barrel off of the frame. Go through some mixed source 223 brass and sort this brass into three batches. The ones that go into the chamber easy, should probably be set aside for some other gun. The ones that are snug will be converted after you set your sizing die. Hopefully you will find some that are big enough toward the base that they will not chamber. Take some brass that was "too big" and convert them first. Back off the 7 TCU sizer die at first and try a round. See if it will chamber. Run the die in just enough such that rounds are snug but can be seated flush with the end of the barrel using with finger pressure. Now with your die set, convert a batch of 10 to 20. Try loading these up and see if you ignition percentage goes up.

    A more aggressive approach is neck up too big and then size down. 30 cal might be enough. Annealing would be strongly recommended.

    The sure fire choice would be to buy some Starline 223 basic, but this stinks given the cost (250 for $91.00) compared to range pickup brass.

    If you want to stick with converting 223, and your chamber dimensions are less than ideal, you may find yourself accepting less than 100% firing during fireforming. The good news is that with neck sizing only, they last a long time and with a break open gun you need a lot less than a guy with a semiautomatic rifle (me).

  9. #9
    Boolit Buddy
    Join Date
    Jun 2011
    Oklahoma / Wyoming
    I keep seeing where guys say to set the case head flush with the end of the chamber, and this is NOT correct!

    If your case head is flush with the end of the chamber, and you have .010 to .015 barrel to frame gap, then that is how much headspace you are going to have! You want your cases to have .000 to .001 headspace at most, which will give you your best accuracy potential and longest cast life.

    When your barrel is closed and locked into battery, use a set of feeler gages to see exactly what your barrel to frame gap is. If your barrel to frame gap is say .008 like one of barrels are, that means that when a case is properly fireformed, the case head should protrude .008 above the breech face of the barrel. Then, when you size your brass, check it in the chamber and using your feeler gages, if you can slide a .001 gage between the case head and breech frame, the case has been sized to much. In this case, back your size die a little further away from the shell holder. You want a gap of .0005 or less when a round is loaded into your chamber.

    The same holds true for the T/C Encore. The more perfect the headspace, the more accurate your rounds will be.

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BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
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