Well the LMG version on he G11 had 3 chambers and it aparently solved he cook off problem.  Would it at least reduce throat wear or heat?

nPlex aren't a valid proposal anymore, specially with FCS fielded. APDS... I'm not sure what would happen with plastic sabot at such pressures

You can definitely make sabots hold on long enough to get past the end of the suppressor and that's really all that matters 

All you really need is something to keep the sabot in place until it's clear of the bore. I've seen pictures of shotgun suppressors around, where the bore is lined with guide rods to do just that. For a rifled barrel you'll want these surfaces to match the rifling.

As for the polymers and pressure, they should be fine. Thirty years ago sabot polymers weren't adequate for service, but they did what they needed to most of the time. These days it shouldn't be too hard to formulate a polymer with the exact characteristics you need. You can do FEAs to figure out what those characteristics are, and do computational chemistry to figure out how to get them. (Computers really are something, aren't they?)

Yeah I know of some guys who have done FEA's on a few sabot designs that look pretty favorable from a strength, function, and parasitic mass stand point (as low as 5% sabot weight to projectile weight) 

It's just a matter of getting everything together to start testing and small scale prototyping at this point.

There's a whole bunch of stuff that's absolutely possible, it's just a matter of the will and funding to get it past the digital validation phase.

All we need now is for the real Elon Musket to stand up and deliver us from this archaic status quo. 

Or something similar sure.

There's kinda no denying that we have a problem at this point.

How we solve it is not my department though.

Revive Springfield Armory.

Regarding l/d ratio, the FN 15mm had really long bullets for their APDS....look at the pics.

Im unsure as to whether a 4mm steel rod would be best (no jacket) or perhaps add a jacket to increase it to 5mm

and as as for expensive tungsten, why not blend it with a steel alloy so your only using 15 grains of tungsten

Lol Springfield was the epicenter of the worst of the worst unfortunately Stan.

The shenanigans they pulled and the good designs they screwed us out of are legendary in their own right.