wil473

Is there a modifier for weapon recoil? I've got muzzle brake attachments that in theory take some of the bite out of recoil. Also, I've got the Gyrojet pistols in my mods, it would be reasonable to make them recoilless.

There is not. There is autopenalty tag (in weapons.xml) and modifier(in items.xml) (if I am correct), but that's just for guns auto-capable. There is RecoilX and RecoilY added by Headrock for NCTH, but it is not entirely speaking about the back recoil.
I could add a modifier to items.xml, which reduces recoil kick impact on energy (RecoilEnergyCostReduction or BackRecoilReduction). That could be added both to guns, and attachments, thus making what you need possible. Though I am always hesitating on adding new tags. But if you see it a good idea... making it is not a problem.