Not just bushmaster. Im having the same problem with my DPMS AP4 as well.
Went to the gun show in Sharonville, OH today looking for a new lock nut... Not a single one to be found.
Going to try the hairdryer in the morning and see if that works. If not, I'll be cutting mine off after I order a new replacement... Thinking about ordering a new buffer tube as well, since I am pretty sure its gonna get boogered up as well.