a)
7 mm TCU cases are made of .223 brass.
I anneal them and use a mild load behind a filler.
What happens if I fire a .223 round in the 7 TCU barrel ?

b) what happens when I fire a .44 mag in a .45 Colt barrel ?

Both in a Contender, both is not state of art, but is it dangerous ?
I think yes, my friend sees no problem.

What do you think ? (better I ask you than risk a test).

waitaminit,

The 7 TCU headspaces on the shoulder, which is not in the right location on the initial .223 case, which is why you're fireforming in the first place.

I recommend seating 7mm bullets out as far as possible, so that you can headspace on the ogive for the fireforming shot, thus keeping the case from moving forward until you can get a proper shoulder.

If you seat a .223 bullet, you won't get proper headspacing. Also, I don't know what that violent "necking-up" is going to do to your necks.

Rick.

In regard to the 7 TCU, when you neck-up for the 7mm bullet, leave a false shoulder below that to engage in the area that the chamber necks-down from the large diameter of the case, to the shoulder cut in the chamber. This false shoulder will set the proper headspace, prevent violent slam-backs and form the brass properly from the breechface forward.

Well, this is 2 different things isn't it?

I know people who fire .223 in 7mm TCU to fireform. They claim no problems but I don't do it. I think it is asking for trouble.

It seems that you are already forming brass in the normal manner. IME, annealing, even of military brass, is unnecessary. Also, so-called "fire-forming" loads can be the same as your regular loads (if, of course, they fit in the case). I form my brass as I shoot it, for fun or hunting. This is a particularly forgiving round (I've got 2 barrels) and I notice no difference in accuracy, which is excellent. So, there is no reason to fire .223 in the 7mm TCU to form (and what a waste of ammo for THAT barrel! )

The .44 Mag in the .45 LC chamber is another matter entirely. You will inevitably get at least some split cases. This just isn't good form. Heck, I've had .44 Mag Remington brass split in the .44 Mag chamber (and factory loads at that!). It can't be good for the gun, you can't get good accuracy (.429 bullet in .452 bore), .45 LC brass is cheap and available (at least in the U.S.). The more I think about it the more stupid it sounds.

I don't know about the 7mm TCU but it's baby brother the 6mm TCU I shoot. to form cases I just get IMI military loads and chamber and fire. I don't seem to have any problem. I began fireforming in this manner at the recommendation of my gunsmith for my 358 Winchester. Again, military ammo load and shoot - 358 fireformed cases. I have had a couple of the 308's split necks but only a couple in all these years.

PaulS

okay, I tried the fireforming of .223 to 7 TCU today, but they did not fire- only the firing pin formed a neat little dent on the primer.
But this altogether is not what we mean with fireforming :-)

Hobie, (question b) you know the situation, sitting with a friend and some beers, phantasy creates situations like:
deep in the forests at the camp fire. the biiig bear shows up, and you have your .45 Contender and ONE round .44mag at hand.
Who will survive, the bear or you ?

I do not believe that anyone would try to make a .45 out of a .44 to save money - how?

I must a bit too old for fantasies since that did not occur to me.

If you have only one round I suppose you better reach for the ax that you used to cut the wood for the fire. Would the bear even approach the fire? What did you do, rub bacon aaaallll over your body?

I suppose that I should try out the .223 fireforming but not wanting to put a .224 bullet down a .284 bore, I'll just try it with a couple of blanks. All other conditions would be the same.

The best thing (and did I not say this before?) is to take empty .223 cases, lube and run into the TCU die. Check for proper fit in the chamber (i.e. the case should allow the gun to just lock up). Then do all the cases you plan on forming. Load with whatever starting load for the powder you plan on using. Go shooting. I see absolutely no reason for special fireforming loads or shooting meal of any kind out of the barrel. Waste of time, I know I've done all that, too.

Good luck.

waitaminit
Probably did not fire because the firing pin just pushed the case forward. You need to seat that bullet out to almost touch the rifling. Some say light rifling contact is better still. If I were doing it, I'd back off the load a bit if I was seating the bullet tight against the rifling.

John, there is no adaquate neck/datum line for the .223 case in the 7 TCU barrel. The cartridge is kept in position by the extractor.
I checked it - Head and bottom of barrel are flush and do not move when I press my finger on it.
But as the primer cap is quite strong, the impact causes the case to move in a circular movement around the extractor claw. This is only a fraction of a degree but enough for a misfire.

I hope this explanation is correct - or my barrel has a flaw.

Your right about the extractor holding the case in place in a T/C. If the extractor is fit correctly that should be enough to fire form. However, I wouldn't depend on it. Expand the case to something over 7mm then back down to put the shoulder in the proper place then fire form, and I would not use a bullet just a filler load. Could save some head separations.