Spaceships 7 and Cannon/Catapult Damage

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We're working on a Spelljammer inspired campaign at the moment, and looking at using GURPS Spaceships (and SS 7 in particular) for ship design.

My current question regards the damage done by Low TL cannons and catapults. Unless I'm missing something very obvious somewhere in SS 7, there is no difference in damage done by TL 6 and under guns, and catapults, versus their high TL counterparts. So we have a TL 5 slow firing 12 cm Gun (equivalent to a 24 lbr?) doing 6dx30 dDamage, and a 5 cm TL 4 catapult doing 6dx12 dDamage.

The closest matches I can find in Low Tech is 6d x 5 (non decade) for a 24 lb cannon, and 6d for a 5 lb Ballista.

I know that the damages listed in SS is based on a Kinetic warhead with a 1 mps base impact. But a 5280 fps muzzle velocity is a stretch for TL 7 guns, let alone TL 5 or less, or for mechanical artillery.

Is there any rules for adjusting damage of these weapons? Espeically more in line with the dDR 10 and that seems to be the upper limit for SM +8 or +9 ships using wood and iron armor.