Ivy Mike
Member
and honestly, the ability of the cartridge to handle pressure is more about the chamber than anything else. Well supported chambers don't generally have kabooms.The True Velocity (teamed with General Dynamics in the NGSW program) composite case (polymer and steel) has a steel case head in it. Combining the compliance of a well engineer polymer to form an excellent gas seal backed up by steel for the structural strength. I suspect the case will survive higher pressures than a brass case will.
Sigs case for the NGSW is a steel/brass highbred and again utilizing a steel case head it has already proven to go well over pressures all brass cases can survive.
Finally Textrons entry to the NGSW program is using case telescoping ammunition and this unique cartridge is supported in such a way as to make case strength almost irrelevant. I believe they are using and all polymer case that will easily out perform brass cases in this application due the the guns design.
Toss any bullet in a fire and the case will fail without generating much pressure and the bullets don't end up going anywhere with any sort of velocity. About the only drawback to polymer cases is that they are single use, but the military doesn't reload anyway.