I love using the ac5 and ac2 combo it feels like a uac that never jams :3 so in this build your tatics would be to continuously fire the autocannons and then alpha strike till your hot and then do some heat managing with the autocannons and srms. The reason for the srms is because if your gun torso is gone you can be a suicidal face hugger useful as you have enough damage to keep on fighting Here is the ac20 version if you are very accurate and patient by having no long ranged weapons to counter those ppcs.
This build can go 1 vs 1 with nearly any heavy mech since I've severly* destroyed many thunderbolts, miserys, and other orions it certainly tears up armor. *disclaimer: you need help from your team mates as well since the orion doesn't have enough armor for itself its just like a urbie big guns, and faster speed then a atlas.
I hope SRMs get better soon. I enjoy running them on my Orions. Build works well. I'm excited to see if it does better after the SRM buff we are getting today.
you can always change the build so it has more dakka fire power rather than missiles so it would be something like this: and even this