I found this button glitch along time ago, but i don't know if it any good, for i have yet to been able to be forced in a situation where i need to use it.
It has the same effect as a BXR, although slower, and possible suiced if it backfires on you.

Combo(default settings): B,L,YY,R
Bump Jump: (RB)L,YY,R

The combination of L after the melee cause you to throw a grenade, and cancle your Beatdown(make sure you melee hits) , then you hit YY it cause you to switch weapons, again cancling(wait till your grenade leaves your hand, or it will never exist and you'll lose a grenade count) the grenade animation and then you shoot. I do not know if this is only an off host thing though. If done correctly from some one elses view it will look like you are throwing an equipment, but a frag/sticky comes out instead. I'll post a video some time soon.

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skadoosh