Brady Campaign vows suit against mfr protection bill
The Brady Center has announced it will file suit over the gun manufacturer/dealer protection legislation.
I can't see a broad challenge. Brady and suchlike places have pushed the legislation that pushed the envelope on Congress's powers over interstate commerce (somehow, having an assault rifle or other designated gun in your closet is a matter involving interstate commerce), and this law involves commerce far more clearly than any of those. Specifically, it involves protecting commerce from state actions, which is at the very core of the commerce clause power.
One possibility might be the claim that cutting off lawsuits after they were filed is a violation of due process, a deprivation of "property" without due process. I haven't done much research there, but it'd at best rescue the lawsuits already filed. Given the the vast majority of ones filed to date have lost anyway, that wouldn't be much of a victory.