A few things worth knowing...
1) I don't think you can KEEP the third gun. When I used I dropped my SKS AND Mosin, but only the SKS was on the ground.
2) Shifting guns around is.... complicated to say the least. I didn't see a way to swtich without dropping. You most likely can't.
3) This MAY work with more than three guns if you repeat the process.
4) I don't know if you can drop the guns on the ground manually.