Military round comparisons

[Tony Williams]

is there anything important to know about the interior ballistics of lead-free ammunition, anything that, vis-à-vis safety, should influence chamber dimensions, etc.?

The key issue with lead-free bullets (by which I mean with some mix of copper and steel - tungsten is too expensive for general use and has its own toxicity issues) is that they are less dense than lead. So if you just keep the same bullet shape you lose weight and therefore BC, other things being equal. To keep the weight and BC the same, the bullet has to be longer. This can cause problems with ammo packaging (the longer bullet may leave less space for propellant) and even stability issues, since a tighter rifling twist may be needed. In fact, with a 6.5mm bullet you might find that a lead-free 123 grain is beginning to push the envelope as far as the maximum length/diameter ratio for spin-stabilisation is concerned - especially when you bear in mind that a tracer bullet will be required, and they are less dense still so tend to be longer than their ball equivalents.

Taking all of that into consideration, lead-free bullets are a PITA for achieving high-BC bullets in a compact 6.5mm cartridge.