Not sure if anyone has looked at this before, but I was interested to find out so had a little look.
A quick background:
I play Imperials and my lad plays Space Marines. Always seems to me that the SM rip apart IG so much easier that IG rip SM, so I thought I would take a dig into the maths. I promise to keep the maths simple.
A SM shoots an IG with a bolter at long ranger and the IG is not in cover. A SM has BS 4 so needs a 3+ to hit (4 in 6 chance of hitting (4/6) or 67%). If the SM hits he then needs a 3+ to wound as the IG has toughness 3. Again 4 in 6 chance of wounding or 67%. The IG does not get a save against a bolter so the chance of a SM killing an IG is (4/6 * 4/6 * 100) or 44% chance of a kill.
When I worked it the other way around it did not look so jot for the IG.
A IG shoots a SM with a Las Gun, again at long range and SM not in cover. A IG has BS of 3 so needs a 4+ to hit ( 3 in 6 chance of hitting (3/6) or 50%). If the IG hits the SM he needs a 5+ to wound as a Las Gun is S 3 and the SM is T 4 (2 in 6 chance of wounding (2/6) or 33% chance). If the IG manages to wound the SM gets a 3+ armour save (4 in 6 (4/6) or 67% of saving). So the actual chance of an IG wounding the SM is (3/6 * 2/6 * 4/6 * 100) or 6% chance of a kill!
This is just some basic maths that I worked out, will work out how much better Twin Linked weapons are when I get time. Someone please correct me if I am wrong as it does not make for good reading. In case anyone is wondering, it works out you need 7 IG to have as much chance of a kill a 1 SM.
Let me know what you think.....