A Minor Controversy Over Cartridges

We’re having a bit of a friendly disagreement over cartridges here, and I’m curious to hear some unbiased (or at least differently biased) opinions from you guys.

Suppose you were putting together a new, cool military style rifle – not for production, but just for your own use and for the fun of building and having it. Semi-auto, detachable 20-30 round magazines, good iron sights, provision for optics, etc. The design is easily capable of handling full-power rifle cartridges, but it doesn’t necessarily need to use any particular cartridge. The question is:

Given that you are not encumbered by a pre-existing magazine design or OAL requirement, what cartridge would you use in a general-purpose individual shoulder rifle?

One school of thought here is leaning towards 8mm Mauser, because it is still relatively cheaply available (and we have a lot of it stashed away) and the gun could be built around cheap and high-quality MG13 magazines. Also, there is a general lack of semiauto, detachable-mag 8mm rifles (G43, Hakim, Yugo M76 – and none of them were issued with >10-round mags…there are also the G41 and FN49, but those relied on stripper clips). The 8×57 cartridge is a good design, and being rimless would not present any particular difficulties in rifle design.

The other side of the debate is to use an intermediate cartridge along the lines of .276 Pedersen or .280/30 (but something for which brass is still easily available, so probably one of the 6.5mm or 7mm commercial hunting rounds). The ammo would have to be handloaded, but it would allow the best balance of firepower and handling/recoil for a shoulder rifle. Any of the common .308 magazines could be used, and with some strategic lightening the gun could be in practical terms a recreation of the intermediate caliber prototypes of the 1950s like the light FAL or early CETME. The specific cartridge to be used remains undecided, though – perhaps 7mm-08, or .260 Remington – or something more esoteric.

What do you think?