I needed a handguard tool...many gun related projects are 3 handed jobs; I'd rate this one a 4 handed job. I had to push down like a mofo on the handguard tool; make sure you got the front part all the way in the handguard cap...then try to get a portion of the back behind the delta ring.
Once you do, continue to put pressure on the delta ring, and give the back part of the handguard a good shot with the palm of your hand. Before you do, though, make sure the groove in the back part of the handguard is over the barrel nut, and the groove in the front portion is over the gas tube.
What makes it hard is the diagonal nature of the Fobus handguards...they just look weird when you first get them.
It's almost a full time job just getting the delta ring far enough back to allow you to get the things on...you have to move it MUCH further than you need to get the regular handguards on and off.
OOPS...I re read you post...the M33s are different from the M44s...sorry!
Without having seen them, I don't know what to tell ya...but I bet a handguard tool would help, if they're anything like the M44s I got the Midway one for $12 with the dealer discount...it makes it too easy to get handguards on and off.