Is this a trick question?
- Once, because then it's different ammo.
Seriously, if the question is how many times a brass case can be reloaded, the answer is
Warm loads, fully resized, fired in a SMLE, maybe as few as 3 reloads. Hirtenberger 7.62x51 brass in my M14, about 6 reloads, My father's 7mmRemMag has some cases he's reloaded 35 times, and benchrest guys often get more than 100 reloads out of a piece of brass.
The chief variable is how much working the brass gets.
- Fired in a loose chamber, with a generous neck, in an action with rear locking lugs, then squeezed back to minimum SAAMI specs, means the brass is getting an awful lot of working. It's going to stretch like crazy. 3 reloads and you're flirting with a head separation.
- The same case fired in a super tight chamber, in an action with properly lapped front locking lugs, and in reloading only the neck gets squeezed 0.003" just enough to hold the new bullet, this case will last a long time.
Depending on the action/chamber design, the ammo's pressure can be a significant factor in case life; but it's not written in stone. Have a look over at 6mmBR.com, these guys get over 2800 fps with the 107 grn MK out of the little case. That's just a couple ticks slower than the .243 The pressures are pretty darn high.