I own an 18" Ultralite50.  I installed the supplied heavy duty hammer and spring that came with it.  The trigger pull is that of a stock AR, and I need to upgrade it to something better.  I have an RRA 2-stage NM trigger which I would like to use, but if I do, it will not work with the ultralite50 heavy duty hammer.  I do not want any parts breaking or be unsafe, so what do I do?  what are my options for triggers for this thing, being as it seems I need to use their heavy duty hammer?  Would rra's NM hammer that comes with the trigger be strong enough?  I need help, as I want to use a real trigger for shooting the .50 instead of this heavy stock AR trigger.  

please help.

the 2 stage bushmaster sells will work with the big hammer and it nice, i use it now on my UL

In my ultralite 50 I used a JP trigger but kept the stock AR hammer spring.  I have had good luck with mine