You can't. If you have the same weapon more and equal than 2 times the game recognise that and kicks you back in the main menu. (So to say you "crash" it with that.)
You can only have all weapons only one time.
From my notes at bit.ly/1rAxrLy:
- each gear slot has the following format:
wwwwxxxx yyyyyyyy zzzzpppq aaaabbbb cccc1111 22223333
- in particular, pay attention to hex labelled 'p': 10-bit placement index (incl upper 2 bits of 3rd byte)
- so if you want to dupe gear, the simplest approach is to designate another piece of gear to be overwritten:
1. get the raw data (6*8 hexes) from the source gear
ssssssss ssssssss ssssssss ssssssss ssssssss ssssssss
2. get the raw data from the target gear slot
tttttttt tttttttt tttttttt tttttttt tttttttt tttttttt
3. replace all hexes from source to target, EXCEPT the hexes corresponding to position; then paste into the target gear slot and poke
ssssssss ssssssss sssstttt ssssssss ssssssss ssssssss