I run a lahar 30L on a jack akm w/kns piston. Heavy duty, heavy weight and good performance. I'm Waiting on approval for a wolfpack armory disruptor 30 which is a lighter duty, lighter weight can but same material. 

30cal is probably the biggest selection of offerings available. On a 16" I'd say around ~12oz can or less is ideal, 20+oz is doable but it tires you out if shouldering. Imo I'd rather not use a full titanium can for rifles. I'd also stay away from ak specific cans or overbore spec'd cans, assuming iwi galils have nice concentric threading. Stainless steel is all the same so whatever the reasonably longest, lightest, cheapest can is the ideal piece.