A Giant Sword, A Shield That Blows Up, and Reactive Armor

[Varyon]

Originally Posted by Sindri

1. It shouldn't deal enough damage to reduce hit points of the shield or TSF.

And note that this is going to be a contact explosion on the shield itself, for maximum damage. I'd probably limit it to (Shield's DR)/2 in maximum damage, just in case it gets detonated in an enclosed environment (which doubles damage, see HT181), such as might result from punching a particularly squishy foe.

Originally Posted by Sindri

2. It should be able to penetrate non-armour-plate BETA DR.

Note if the above damage is insufficient for this, you can state the explosive plates - which appear to be designed more for offense than defense - are actually shaped charges with metal liners, which can justify anywhere up to a (10) Armor Divisor against the target (no divisor against the shield it's mounted to).

Originally Posted by Sindri

3. It should be reasonable given plausible REFs for the TL and eyeballed dimensions of reactive armour patches.

I can't imagine casing/etc taking up more than 10% of the patch's weight (although I could be mistaken), so going with that we can fill it up with a 2:1 mix of CL20 and HMX (this mix being the highest power TL 8 explosive that's safe to transport that I can readily find online). The end result is going to be that the explosive patches have overall REF of around 2.0.

A typical shield scaled up to SM+6 is going to have DR 40 or so, but ST 300 is more appropriate for an SM+9 character, so scale shield weight up to that. An SM+9 shield would have DR 80, but with only 1/3 the surface area this gets boosted to DR 160. So, your shield is safe for a 50d or so explosion. That's around 8.7 lb of armor patches being detonated at a time. If 50d cr ex (arguably maximized for contact) is enough to punch through and appropriately injure typical BETA's, you're set. If they have too high of DR for this, give the patches sufficient armor divisor to get through. If they have too high of HP, consider giving BETA's a Vulnerability to explosions. If this is too much damage, either have fewer patches explode per hit or use a lower-yield explosive. This explosion will occur concurrently with the punch/shield bash, so each should have to deal with armor separately (it may be possible to delay the explosion so that it functions as a follow-up instead, in which case a punch that gets through DR can result in the explosion not having to deal with such). Note that, with ST 300 giving 31d thr and 33d sw, this explosion is probably the mecha's best melee attack - which I suspect was indeed the intent.

EDIT: As for the swords, you can scale them up to SM+9 (or SM+8 if it normally has MinST above 10) for weight and damage, SM+6 for Reach. So a thrusting broadsword would do thr+60 imp, sw+30 cut, which works out to around 48d imp, 41d+2 cut (yes, the scale is a bit broken here).