Clamping new armored cable run to existing conduit

[Paul]

I'd like to run a new circuit of armored cable ("BX") alongside an existing conduit. 1/2" conduit clamps don't get tight enough to hold the armored cable very well. Does somebody make a clamp for this application? Would fastening the AC to the conduit with a plastic cable tie be NEC "legal"? How about stainless steel cable ties (i.e. fireproof) ?

TIA, Paul

[RBM]

They make BX (AC) straps. They look like the ones you have, only smaller