Walker stayed in Syracuse after the Stars released him, returning to a position in the postal service. Around this time, a former Syracuse University professor, Dr. Joel Gibert Justin, had been experimenting with firing artillery shells with gunpowder rather than compressed air, culminating in his failed invention the "Justin Gun". Fascinated, Walker designed and patented an outer casing in 1891 that remedied Justin's failure. The first of his four patented inventions, Walker invested in the design with hopes it would be in great demand, but the shell never garnered enough interest.