I've finally managed it. I now use motes to level up every blue weapon before dismantling. Some guy had a good tip to buy year 1 exotics (costs an exotic shard- but you get it right back when you dismantle, so it's basically 2500 glimmer for 6-8 weapons parts) and I've been constantly buying Thunderlords (machine guns level fast), leveling up, dismantling. Because yeah, the best way to play Destiny is to sit in the tower leveling up and dismantling- versus firing a gun.... But at least I think I'll have enough parts to level up and test all of those guns in the vault.....