fnuser wrote:

tough on extractors?

It didn't seem to hurt the extractor on my friends Winchester, but once he saw the cases he didn't continue to fire the .222s in it. Prolonged abuse would probably damage them though.

Back to the 270 in the 3006 - the cartridges are close enough to work without causing problems - other than a lack of accuracy. I fire form 308 cases for my 358 Win by loading a light load with old .30 cal bullets and fire them in the 358. It does a good job forming the case and the rifle is easy to clean after the process.
The smith that made my gun told me to form this way... and it works.

Not meaning to second-guess your gunsmith, but I do question the advisability of sending undersized bullets rattling down a bore.

You might want to open the necks with your .358 die and seat .358" bullets over starting loads with the bullets seated out to touch the lands. This holds the head of the case properly against the breech block and allows the case to expand forward (as it should) rather than stretching the web, which can cause premature case-head separation.

I think I would just buy new brass !!!

IMO fire-forming is best achieved using the false shoulder method ....... the firing pin can/will move the case forward even with bullets seated into the lands.

The outcome would have been a lot worse ig the guy in the first post had tried to fire 30-06 in a .270....

I doubt that a .30-06 round would chamber in a .270 rifle due to the greater bullet and neck diameter. That is a good safety factor.

There was a warning in WWI to American G.I.s not to attempt to fire German 8mm rounds in a 1903 Springfield or a Model 1917 Enfield. The 8mm round being shorter than a .30-06 would chamber in a .30-06 and be held by the extractor. Firing would damage the rifle and probably the shooter. In fact, some of the reports of "low number" Springfield receivers failing were attributed to the improper use of 8mm ammo. All the best...
Gil

chambered221 wrote:

I think I would just buy new brass !!! IMO fire-forming is best achieved using the false shoulder method ....... the firing pin can/will move the case forward even with bullets seated into the lands.

Since Midway offers .358 Winchester brass, I too would rather start there. It would solve the issue of mistakenly dropping the wrong rounds in the pocket just because the head-stamp would be correct!

I also agree that the false shoulder method is usually a better way of forming brass if the size difference isn't too great. The steps and expander buttons necessary to expand the neck in stages (I would guess that the shoulder on the .308 brass would crumple if you expanded the size too quickly) from .308" to .358" would be excessive and require annealing at least twice. Were I forced to do it this way, I would start with a .321", jump to a .338", a .358" and finally a 9.3mm (.366"). Then once again using the .358" sizing die neck the case back to .358" leaving just enough neck-bulge to hold the case firmly against the bolt-face. The problem is that these steps would work the brass excessively and likely lead to neck-splits.

As to the firing pin moving the case forward when the bullet is seated touching the lands; if the bullet is firmly against the lands (not jammed into them) it is unlikely that the force of the firing pin spring would move the case forward enough to make any real difference.

Well, I may someday have to buy new brass but for the forseeable future I have more than I can shoot. Never had a problem with the brass - I did split a few of the cases but I chalked that up to old brass that was passed off as once fired.
The gun and ammo still shoots sub caliber groups (center to center).