Fire forming

[MakeMineaP99]

Background:

I have a 6mm TCU on a Ruger 77 action. The parent cartridge for the 6mm TCU is the 223 Rem. The 6mm TCU is similar to the 6mm-223 (223 necked up to 6mm), except the case taper is removed and the shoulder is improved Ackley style. As such, you take 223 Rem, neck it up to 6mm, which is by definition the 6mm-223, then fire form to remove the taper and form the 40* shoulder for the 6mm TCU round.

Methods:

There are two methods of fire forming. The first method uses the use of a fast burning pistol powder, Bullseye, Clays, etc, with a filler, cream of wheat is popular, with a wax seal of the case mouth. Use pistol primers and about 10 percent of the case capacity for powder charge. For example, 30 grs capacity, 3 grs of powder. Depsite what some "experts" claim, you can over charge the case, since the filler acts to create pressure, as the pressure is needed to form the case. Don't just fill the case up with powder. If you are getting sooty cases or imcomplete fill out, work up in half grain steps as you would working up a load until you get perfect fire form.

The other method is to use a medium load, in between start and max, with ligher weight bullets and shoot as normal, resulting in fire formed brass.

The $64,000 question:

Which do I use?

Well, that's a very good question. I'm of the opinion to use the former method, as the latter method does cause wear and tear on your barrel just to fire form brass. You can use the fire forming step as productive use of the rifle, but keep in mind it opens up another variable. For something like a 22 or 6mm, you're probably looking at somewhere between 750-1500 rds of barrel life, so fire forming 100-200 pieces of brass to your chamber is going to eat up a good portion of your barrel life.

There you have it, the quick and dirty on fire forming.

[AdamN]

When I was playin around with stuff like that fireforming was used for the barrel break in, (another subject)

Using a pretty stout load , loading long so the bullet would be into the lands.

This was forming Lapua 22 russian to 6mm ppc

Fireform about 50 rounds of brass and with proper care that brass would last the life of the barrel

[MakeMineaP99]

My barrel came to me broken in, so I can't speak about barrel break in and fire forming. Seems there's several opinions on barrel break in.

Yeah, with a bolt gun, you don't need very much brass. I have probably about 1000 for the 6mm TCU, but this is a varmint rig, not a benchrest rig. I assume since you were into PPC, you were shooting benchrest, which is way beyond my scope right now.

[AdamN]

That straight sided case design will really make the brass last longer, wont stretch much at all.

If youre doing the cream of wheat thing just bump the shoulder back to where the action will just close.
If not the firing pin will drive the case forward and it will tend to stretch the case body instead of just blowing the shoulder to the proper shape

[JLarsson]

Sometimes, you can work up fireforming loads with good velocity that are quite accurate as well. If so, then you can just shoot the thing and enjoy the fact that you're having your cake and eating it, too.

And Adam's observations about how much to set the shoulder back are spot on. Since you're blowing it out, however, it's possible that you can't actually cause the shoulder to contact the forward part of the chamber when firing. Since you're shooting a Ruger 77 with a claw extractor, that may be enough to hold the case head to the bolt face while firing. If not, and if it becomes a problem, the only other thing I know to do is expand the neck one size (or two) larger - say .270 or 7mm - and then neck it back down to 6mm, being very careful how far down the neck you go, creating a step that acts as an artificial shoulder. The downside is the extra working of the brass in the neck and, in this case, the possibility of splitting the necks or collapsing the shoulder. Since you've already got 1,000 formed cases, I'm betting the "load and fire" method works pretty well with that rifle.

For my 7mm TCU Contender handgun barrel, I just expand the necks and load with 120 gr. Hornady bullets over H322 and shoot them. That's my hunting load and it's quite accurate to boot. It shoots the same whether fireforming or using formed cases.

[MONTEGOD7SS]

The only one I've seen done personally is a .35 Whelen Ackley and it was down with full snot loads. Load in a standard .35 Whelen boomer, out pops an empty .35 Whelen Ackley case. Good to go.

Your CRB status might be in jeopardy if you are wasting powder and primers just blowing cream of wheat out the end of the barrel and not at least taking a poke a something. Just something to keep in mind.

[Tailgunner]

The only one I've seen done personally is a .35 Whelen Ackley and it was down with full snot loads. Load in a standard .35 Whelen boomer, out pops an empty .35 Whelen Ackley case. Good to go.

Your CRB status might be in jeopardy if you are wasting powder and primers just blowing cream of wheat out the end of the barrel and not at least taking a poke a something. Just something to keep in mind.

The rimless Ackley's (and most other "improved" varients there of) use a slight crush fit at the neck/shoulder junction to control headspace (that's why you have to set the barrel back when converting a chamber to a improved design).
Now when you move up to a Rocky Gibbs design, you have 2 choices for controling HS, 1 is to create a false shoulder, and the other is to hydroform the brass to a 95% and than fire to finish forming.
On a rimmed or belted case, you can get very creative on the shoulder/neck movement, as you have something else controling the HS location. See samples below (Improved than Standard photos)
http://i81.photobucket.com/albums/j212/Tailgunner1954/3-21-09004.jpg
http://i81.photobucket.com/albums/j212/Tailgunner1954/3-21-09006.jpg