High Power Chambering. That would either be a change from 8P(f) +5 AP to 8P -1 AP or 8P(f) +5 AP to 10P +4 AP, depending on how you see the HPC mod working.
I doupt there are many GM:S who would allow you to HPC mod a gun that can only fire fletchette ammo.
Just start using AP fletchettes that gives you damage code of 8P 0 AP
Well, it's War! A lot of the rules are only half thought out. There's nothing to stop you from modding an Ares Thunderstruck with HPC, even though it doesn't even use a standard explosive propellant...
Honestly though, it does make some sense to mod up even flechette as HP, if you read the entry. It just uses a more expensive propellant in the round and a heavier firing chamber in the gun to deal with the extra blast force. It could easily be something applied to any type of full metal killing round.
