The systems I have played tend to have a fairly standard set of rules for weapons- as you might expect given that there are a limited number of traders and they need to be able to sell to players across different systems for their work to be viable.
The largest system I've played ( The Lorien Trust, about 5000 players at large events, weapon check guidelines here ) uses the following standard:
- Maximum one-handed weapon length of 42".
- Two handed weapons must be used two handed at all times.
- At least two inches from tip of weapon to tip of core.
- At least one inch between core and striking surface of the weapon - this is the guideline I have used, but I think sometimes with lighter cores this is less of an issue.
- No stabbing at all by anyone ever.
- Bows users must pass a basic competency test ( because the bow is non-padded equipment )
- No core in thrown weapons.
The system I have been playing most recently ( Profound Decisions, Empire, around 1000 player events, weapon guidelines here ) has a similar standard but they do allow stabbing spears ( at least 6" of soft foam at the tip ) which can be used one handed but must only be used for stabbing.
The important thing in both systems is that all weapons must be checked by specialist staff before they are used and that no weapons that have not passed check should be in the game area. A weapons checker has the right to judge a weapon unsafe in their view even if it conforms theoretically to the guidelines. There is usually some visual indicator of check ( UV stamps or coloured bands are examples I have seen used often ) and weapons checkers have the right to check any weapon at any time and typically you have another round of weapons check on the way into a battlefield. This is particularly important because even well made weapons will break with use and one that passes on Friday may have been stood on or damaged by Sunday morning, rendering it unsafe.
Also having refs on the field during combat to ensure that fights are safe and fun for everyone is essential. Anyone using a weapon that is clearly unsafe or using a safe weapon in an unsafe way needs to be pulled up and the weapon/player removed from the field as necessary.