Stratasys makes rocket engines and gas turbine blades with DMLS, for whatever that’s worth.
Robert Hofmann GmbH has utilized 3D printing technology to create a fully functional cylinder block for a Volkswagen engine.
The pounding of 4-cycle combustion is probably pretty close to the pressure excursions of rounds being fired...
It takes more than just sintering it together to make those things. That said, it also looked to me that there were little voids in that picture - though that could be just the surface ripples.