I would like to suggest a couple of additional rules which would help players influence the outcome of Arms finds.
Proposal #1: Character Perks
A character with the Explorer perk adds (20 + Luck attribute) to the arms chance.
The Ranger and Scout perks each add a flat +10 to the arms chance.
In order to rate the bonus, a PC must participate in at least 50% of the salvage operation or be the "finder" of a cache. Multiple perks can add to the same arms roll, but each perk can only be added once.
Example: Tom, Dick, and Harry locate an abandoned bunker and work together to harvest the find. They can each contribute a different perk, but if all three have the Scout perk it still only counts once.
Proposal #2: Critical Success Margin
Critical success on an Arms roll is one-tenth the total Arms Chance or the main character's Luck, whichever is higher. If the crit margin or less is rolled, you get two rolls instead of one on the Arms Table.