FLK is determined similarly to AC, SRM, LRM, TOR, etc.
For each range band, you take the damage values of all FLK capable weapons. You adjust for heat, divide by 10, and round normally.
Examples.
WFT-1 Wolf Trap. Has an LB-10X capable of FLK. It has no heat problems (14 maximum heat buildup -4 = 10 heat dissipation). LB-10X is a cluster weapon and a roll of 7 on the cluster chart gives 6 damage. The -1 to hit of the LB-10X cluster ammo adjusts that to 6.6. 6.6 heat adjusts to 7 (heat adjustment includes a round up to the nearest whole number, so even though the heat build-up to heat dissipation doesn’t change anything, it still hits the round up). 7 divided by 10 is 0.7. This rounds normally to 1. LB-10X is capable of reaching long range in BF/QS, so that’s a FLK1/1/1.
An LB-20X by itself is a 13.2. 12 for the cluster result, 13.2 modified for the -1 to hit bonus. Unless there are other FLK weapons though, the LB-20X will still only give FLK1/1/0 because it’s a round normal and it cannot reach long range in BF/QS.
ANH-2A has four LB-10Xs. This would normally be 6.6 damage from LB-10X * 4 of them = 26.4. 27/10 =2.7, rounds up to 3 and would give a FLK3/3/3. Unfortunately, the ANH-2A has heat issues. 26.4 * 17 heat dissipation / (26 max heat buildup – 4) = 21. 21/10 = 2.1 rounds normally to 2. FLK2/2/2 is the result for the ANH-2A.