I have no issue with the gun barrel or Bonecrusher's crotch. Bonecrusher's crotch gets a bit fiddly during mid transformation. I initially had trouble making it connect because I kept on squeezing the two halves of his pelvic girdle together, but I actually find it better to just squeeze from his hips; i.e. the upper part of his legs rather than the crotch pieces themselves. Works on mine anyway.

Anyway, here are some more comparison pics between Devastator and other large Transformers.