I see what the problem is now- I've been using the Arsenal tables for all weapon stats.

Having a future version of the Frag-12 be an Ex-Explosive round for shotguns seems plausible since the damage of shotguns are powerful, add an explosive charge and we have horrible damage potential to the victim.

A possible idea is to add a small 'splash' damage to anyone within a meter or two of the target, say enclosed areas or if in melee with the target. But giving it an explosive radius of a grenade is a bit extreme. It is still a shotgun, not a grenade launcher.

A little note on math

First, impact armor is less than ballistic since the gimmick-formfit only provides 2 points of impact (raising the max impact from Body*2 to body*2 +1) where ballistic is easier to mix-match together to the maximum of Body*2 +3 without encumberance.

AND, it takes +6 ap to negate +2 DV on average (+8AP to buy off 2 damage), in most cases the NET DAMAGE even with 5 more armour will be positive.

And finally, only dwarf mages tend to have more stun boxes than physical boxes. Not only is stun damage better in every possible way (dead targets can't be interrogated and murder means more shit (and notority) flying your way than a simple bruise) since you can always just execute snoozing bodies once combat is won.

Flechette rounds and shottys are better in nearly every aspect except your need to abuse weapon mods some more to bursts to work for shotty recoil.

Nothing stands after a long burst with a moddded SPAS. (9p(f) base + 5dv long burst +1-5 net hits for a regular sam with 20+ attack dice pool = 15-20 stunboxes that takes more than 30 points of armor will keep you awake, even more if you plan to stay standing.

Yeah sadly those don't have the correct AP values for flechette, even thought that book came out after the change.

This however totally contradicts the RL effectiveness of shot vs. armor. That's why it has been changed to +5. Combined with the +2DV this is still too much armor penetration IMHO since Impact armor is used which is generally lower than ballistic. On top of that the writers can't do basic math. -1+5 still is +4 and not +5. On average +2DV more than cancels the +5 AP, except for checking whether the damage remains physical.

BTW is shot=flechette? I don't think so because flechette is much too expensive, and it has no spread. IMHO shot should cost the same as regular ammo, gets the benefit of the choke and the drawbck of the reduced range. Flechette should work in shotguns just like in other weapons i.e. use slug range and no choke.

It's a typo. There's a couple of weapons that don't properly list values when using flechettes. It should be +4 AP, otherwise the Remington 990 would be -3 AP when using slugs. I've not seen anything in the reading that AP values supersede the weapons AP value and I see nothing that indicates that the weapon's AP value applies only to one type of armor, so a weapon with -1AP using flechette should be +4 AP not +5 AP. Though I welcome anyone that can point out the flaws of my logic to do so. This is just how I've interpreted the rules.

Yeah, someone on the devteam fails at doing math - most shotguns are 7p ap-1. With flechettes in them, it goes to 9p ap+4.
The confusion comes in where some shotgun models are -only- able to fire flechettes, and have that damage code base.(the pre-factoring).
Somewhere along the lines, someone went 'dur hurr, ap+5 on flechette, copy, paste, done' and forgot about the basic ap-1.