Physical projectile damage (research) is not receiving infinite research correctly. It is compatible with vanilla turrets up to level 6, but with infinite research (7+) the vanilla turret begins to receive a 70% damage bonus; But the turret added by this mod gets a 40% bonus here, meaning it remains 30% weaker than the vanilla turret... I don't think it is intentional for balance, I think it should be fixed...

https://wiki.factorio.com/Physical_projectile_damage_(research)

table.insert(
data.raw["technology"]["physical-projectile-damage-7"].effects,
{
type = "turret-attack",
turret_id = "gun-turret-2",
modifier = "0.7"
}
)

0.4 should be 0.7

you are right, fixed in v1.0.7