JHP = Jacketed Hollow Point
HPBT = Hollow Point Boat Tail
JHP-BT = Jacketed Hollow Point Boat Tail
OTM = Open Tip Match

JHP and HPBT are simply terms that describe bullets by a couple of specific or relevant features.  Not all JHP bullets are HPBTs, because some JHP bullets are flat-base, and others have a boat-tail base.  And I suppose it would be possible to make a HPBT without a jacket, but AFAIK that's never been done.

OTM is a term that was invented by terminal ballistics researchers to be politically correct for the military when describing JHP match bullets.  The Hague Conventions restrict signatories (of which the US is not, but we follow them anyway) from using bullets that are *designed* to expand.  Conventional JHP designs are indeed *designed* to expand.  OTM bullets, though they do have a hollow nose, are NOT designed to expand; they are designed to be accurate, and the open nose or tip is a function of the manufacturing process.  OTM bullets don't mushroom at the nose like a conventional JHP.

Using the term OTM helps the military distinguish between the two bullet types, and makes dealing with the lawyers easier.  You'd be surprised at how seemingly minor variations in wording make a HUGE difference in how something is treated.

-Troy