Armour vs armour piercing bullets


You've helped me a lot so I come to you with another noob question :)

Enemy in battledress with Armour of 29.
Team sniper with gauss rifle and special ammo (ARMOUR PIERCING DISCARDING SABOT) has 5D dmg and 21 AP (6 normal plus AP trait equal to triple the number of damage dice it rolls.)

2 situations:
He hits and rolls 22 for dmg. How much dmg do I apply? Armour 29-21 AP, so effective armour is 8 and the final dmg is 22-8=14?
He hits and rolls 14 for dmg. Effective armour is 8, so final dmg is 6?

Additional question.
In CSC you can read:
A weapon must have a listed magazine cost in order to be able to use the ammunition in this chapter. In addition, the following weapons may also not use this ammunition.
One of the listed weapons is Magrail Weapons.
Gauss description: (...) rifles fire high-velocity projectiles using electromagnetic rails.

IMO it is kind of magrail weapon so you can't put special ammo there in the first place. Am I right?
Rules as written. You are correct. A Gauss weapon is not a Magrail weapon.

In other fiction Gauss weapons are often described as firing as small diameter projectile or dart - but in the Mongoose version the description makes no mention of that - so while I am personally suspect of the use of APDS in Gauss weapons rules as written permit it. I think the cost is incorrect as APDS is cheaper than HEAP rounds - so I would probably charge double base cost in my games. In your Traveller Universe you are free to include or modify the use of these variant ammunition at your discretion - I for one allow HEAP rounds in snub pistols and accelerator rifles - as this was an option in earlier editions of the rules and at 10x cost per mag is not something to be fired lightly.

If the weapon becomes too dominant - remember it is a big obvious gun banned at Law Level 3 - and totally impractical outside of a war zone - as your PC is shooting a Battledress equipped opponent I can only assume it is a War Zone.

Magrail weapons only refers to the Magrail Pistol and Rifle from CSC. Which is strange as the higher TL weapon is in many ways inferior to the nirvana that is Gauss weaponry.

I haven't moved up the gun tech tree yet beyond advanced.

Four millimetres is pretty thin for discarding sabots, and you're really into needle territory, or possibly nail gun.

Presumably, crystaliron is harder than tungsten.

I thought the magrails were shuriken gun equivalents.
I agree that RAW would allow the Gauss to use specialty ammo...hopefully the 2023 Update to the CSC will correct this.

Until then, I'd house-rule the exclusion list to include Gauss and Gravitic weapons like Mag-weapons are.

First, it's consistent with the Gauss Rifle that was introduced in LBB4, which did not have alternate ammo available. That book also intro'd the ACR, which did offer DS and HE rounds. So let's look at the MGT2 ACR with APDS and your examples above.

The ACR using AP would have 3D damage and the AP3 trait, using APDS; 3D and AP9 trait plus 490m range. Compare that to the Gauss Rifle's 4D, AP5, and 600m range. The interaction between the amount of damage, the ability to penetrate armor, and at what range you can do those things, makes more sense. Even looking at the Sniper Rifle using APDS, it would have an AP14 trait, but the Gauss Sniper Rifle can still put more potential damage further out (almost twice the distance).

It definitely benefits an armor's Protection score; and I don't think that's a bad thing.

Just seems to make more sense to me :)