Mpi-K East German Assault Rifle. The reason why the lower handguard is wood is because in the 50s and 60s, the brown plastic handguards were melting because of the hot barrel on the rifle. The East Germans then decided to use wood as the lower handguard material. It wasn't until the 1970s that a heat resistant bakelite to use on the lower handguard.
what you do to fix this is
1. export the model as a JAVA file
2. Import the JAVA file into a fresh window of toolbox (the armor should be squeezed together and looking like a messy clump)
3. export as a JAVA file again
4. Enjoy your fixed armor