This is me pulling together my responses to this thread.
This is basically pulling together rules concepts from a few different places:
- the idea that bucklers (shields held in the hand) are treated like weapons, shields strapped to the arm are treated much more generously and don't fall off if unreadied (or even if destroyed to less than -10xHP!).
- the ready time of an unreadied shield from B382.
- the BL-based limits on parries from Parrying Heavy Weapons, p. B376.
So here it is all together, slightly changed to reflect some further thought.
Blocking Heavy Weapons - A sufficiently heavy or forceful attack can overwhelm a shield. Bucklers can block attacks up to your BL. Shields can block attacks up to your BLx2. Attempts to block anything heavier fail automatically; the attack sweeps your shield aside and damages you normally. In addition, a buckler is dropped; a shield is still strapped to the arm but cannot be used to Block until a Ready action is taken to re-grip it. If the Block is made by the DB of the shield, suffers damage and provides it usual cover protection (DR + HP/4, see Damage to Shields, p. B484).
- Optionally you can let every block provide shield DR/HP as cover if the roll succeeds. I can see some flaws in this - you basically get a roll to get cover DR, and with a sufficiently good shield this can let you block anything. Pretty much any Slam will do no damage to you, even if it's way to heavy to get Blocked. That makes a lot of sense for, say, a man with a large shield blocking an ogre or a bull or something, but a lot less for a halfling with an SM-2 light shield blocking a charging dragon. Especially if it's a nearly-invulnerable faerie-material shatterproofed metal shield. Or a Force Shield - it's sci-fi tech but provides DR 100 and can attempt to block anything, ever, regardless of the weight, and gives you +100 DR if you try; that's especially useful with an All-Out Defense (Double) or when you can't risk Dodging. It feels silly with, say, a 2# light shield providing some extra DR versus a giant's sword blow but your 3# broadsword doesn't do anything but get swept aside without slowing the attack. I'll have to mull that one over.
- It's odd that making your roll marginally is better than making it well - the reverse of the normal case with Block, where a marginal success gets your shield clipped and possibly causes knockback as well. You can fix this by inverting the odds (so if you roll under 3+DB of the shield) is possible, too - but it's an inversion you'll have to remember to apply before you roll.
Basically, you can choose to try to Block a too-heavy attack, but all you get is a roll to see if you get the shield in the way or not. If you make the Block roll you may get some DR from the shield (which gets damaged doing so).
This will work very well with the rules I use for BL-based parries.
Also, apropos blocking and parrying heavy weapons, here is a fun, heroic parry rule:
Critical Success On Parrying Heavy Weapons - When attempting to parry a weapon that exceeds your BL limit for parrying or which automatically breaks your weapon, if you roll a critical success on the parry you somehow avoid the attack hitting you. Your weapon may break, but whether it breaks or not it deflects the attack just enough to miss you. Handle breakage and other effects of normally per Parrying Heavy Weapons, p. B376.
- This can give very unrealistic results - parrying dragon's claw with a cheap dagger successfully, or parrying a charging bull with a sword. But it's kind of heroic, and it gives that bullet-stopper bible or lucky move saving you against all odds effect of fiction. If you use that with the inversion mentioned above, the DB of the shield applies in the die range above the critical successes.
Both of these could use some playtesting, so if you try them out let me know how they work and give me any feedback you can. Thanks!