Hoping to get some guidance on this one. I have a .936 barrel with a fairly beefy gasblock on a Mega SBU billet upper. I doesn't touch the handguard but there's about enough clearance to slip a business card between. No muzzle device, but I'm still wondering if it's too close during barrel whip. I can simply go with a micro gasblock if necessary, but not sure if I'm worrying for nothing.

Thanks

It can indeed be a problem, barrels whip around a lot. The other issue is that if you put any pressure on the hand-guard it my deflect a bit and contact with it. Heat and expansion can make that worse. 

Agreed. Going with a micro gasblock.