So, as was requested/mentioned earlier, some folks expressed an interest in a tutorial on case forming from .223 to other cases. Since brass availability seems to be a fickle thing these last few years, it would seem a interesting topic to cover. I apologize in advance to those who are bandwidth challenged, but a photo says a 1000 words...
Okay, first we start off with a box of nasty, dirty, range pick up, military brass.
Here in the States, when there is some idiotic run for components going on, a box of a 1000 of these cases (already cleaned and deprimed) runs about $35. You'll have to remove the crimp, but for those who are not already aware, these cases (Lake City) are very high quality, and extremely strong. These were range pick ups, and had to be run through my wet, SS media tumbler...
Okay so you've got some clean cases. The first step is basically bumping the shoulder back to that of a .221 case. This is done with a .221 FB form die, and are (not surprisingly) very inexpensive. I think mine ran about $28. Since .221 is the parent of a great many cases, I assume that accounts for the lower price of this form die; so many people use it, that they make and sell a lot of this die. At any rate, this die is really short, and so you will need an extended shell holder (10E for RCBS).
But, with that you just lube the case and run it into the die.
As you can see, there is a lot of excess material. This can be taken off with a hack saw (as the die is hardened steel, it won't hurt the die). Preferably, the hack saw should be somewhat dull (no, not daft, dull) since brass is soft, a new hacksaw blade tends to cause more problems with it galling. With a slightly dull one, you can take the excess off in one stroke. You'll need to leave some of the case proud, so don't try to cut it off right at the die. Once the excess is off, then you'll file it flush with the top of the form die. Again, the die is hardened, so it won't be harmed by the file, and you're best off using a slightly older file; one destined soon for the trash heap.
Congratulations, you now have a .221 case ready to be full length sized (after deburring the case mouth). The case mouth will be slightly out of round, due to the force of the hack saw, but the FL die will resolve that issue.
From here, the steps are similar, and repeated for taking it down from .221 to .20, and then .17.
Here is a case being taken down to .20 caliber (incidentally, a 17 Mach IV form die brings a .221 down to .20; a perfect way to make 20 Vartarg brass). Form dies are expensive, so 17FB seating die, would probably suffice. I use form dies when I can afford it though; just less head aches and having a dedicated die helps keep everything set they way I prefer it. (The Mach IV form die was close to a $100 when I bought it, so I'm not sure what they go for now).
You'll notice, the extended shell holder is no longer needed.
From here, the case can be run into a 17 Mach IV FL die and then trimmed, necked turned and prep'ed for loading.
As you can see, there isn't a whole lot to case forming, it just having the right dies to do it. Some will use seating dies form various cartridges (BTW, Redding has admitted that their seating dies are also used as the basis for their form dies) and others will use form dies. It's really a matter of how many cases you are willing to lose in the process, and how severe the forming is from the parent case.
I would have shown a full try of 17 cases, but alas, these cases are not intended for a 17 Mach IV. Actually, they're heading off to Muir for his .300 Whisper (now known as the 300 AAC Blackout), so they were left at .221 for him to neck size up to .30 caliber.
Hope this helps, and gets some guys thinking...