|That Crazy Alchemist|
I think the idea is that Lead Blades means "blades made of lead" not "leading the blades" (tho i prefer the later interpretation), and weapon made of force is not made of lead, but thats just the spell's name.
I mean, if it actually transmuted blade into lead it would deal less damage cos it would be too soft to hold an edge.
The trick is the sword created by the spell Force Sword is a spell effect and a force effect. Secondly(minor point), duration is normal rather than instantaneous meaning the sword isn't permanent.
Lead Blades is a personal spell.
likely only the Occultist has both on their spell list.
Offhand I'd say sure (once) but having spells affect other spell effects is very tricky territory usually reserved for metamagics, dispelling, etc. My rule sense says 'no'. It would take more research on my part to make a stronger statement.
Here are the relevant entries for the spells in question:
You create a +1 longsword of pure force sized appropriately for you that you can wield or give to another creature like any other longsword. At 8th level, the sword functions as a +2 longsword.
At 13th level, it functions as a +3 longsword. A force sword cannot be attacked or harmed by physical attacks, but dispel magic, disintegrate, a sphere of annihilation, or a rod of cancellation affects it.
If a creature you attack with the sword has spell resistance, you must attempt a caster level check (1d20 + your caster level) against that spell resistance the first time the force sword strikes it. If you fail the check, the spell is dispelled. If you succeed, the weapon has its normal full effect on that creature for the duration of the spell.
Lead blades increases the momentum and density of your melee weapons just as they strike a foe. All melee weapons you are carrying when the spell is cast deal damage as if one size category larger than they actually are. For instance, a Medium longsword normally deals 1d8 points of damage, but it would instead deal 2d6 points of damage if benefiting from lead blades (see table below). Only you can benefit from this spell. If anyone else uses one of your weapons to make an attack it deals damage as normal for its size.
Omitted the chart at the end.
As a note, neither spell is a conjuration effect. I am actually surprised at the line that allows the Force Sword to be handed off, that is unusual for a non conjuration. That said, there is nothing in precedent or in the spell descriptions which indicate these two spells will not interact with each other as stated (I have not scoured any FAQs however for this situation as I do not recall any that would be relevant to review). Of note, however, is that Lead Blades is a Ranger spell only and personal range. Force Sword is an arcane spell on multiple lists.