So... what is the diameter of the beams? Millimeters? Centimeters?
What about heat, and for Fusion, radiation?
Just idle thoughts at 03:00.
What about heat, and for Fusion, radiation?
Just idle thoughts at 03:00.

So... what is the diameter of the beams? Millimeters? Centimeters? What about heat, and for Fusion, radiation?
I'd say it's just a man-portable particle beam generator (effectively) of maybe 1mm
well it's held to have very serious recoil. on the other hand it's not held to be a nuke or a anti-armor artillery piece, it seems to be just a heavy-duty anti-personnel tool. so I'd say it's just a man-portable particle beam generator (effectively) of maybe 1mm able to penetrate any man-usable armor (and probably any armor at all). think of it as the LAW or Javelin of its setting - a company-level anti-fortificaation "heavy" weapon.
This depends on the version you play...on the other hand it's not held to be a nuke or a anti-armor artillery piece
MGT1E core book, page 102:
FGMP: (...) fires what amounts to a directed nuclear explosion. (...) FGMP emits 2d6 x 20 rads, which will affect everyone in the immediate vicinity.
Except it becomes the "standard" infantry weapon for TL 14-15, as far as I recall.
fires what amounts to a directed nuclear explosion. (...) FGMP emits 2d6 x 20 rads
If you read the other answers in the thread, you will find that the "by the book" Original (Classic) Traveller answer of 2cm diameter was given by Dolphin in a Robot Suit 7 hours and 7 minutes before your post. It is the post immediately before yours.
Tech level 13: All infantry is generally now in combat armour and equipped with gauss rifles. Battle dress is issued to selected assault troops.
Tech level 14: A higher proportion of the infantry is equipped with battle dress, and the standard small arm for such troops becomes the PGMP-13.
Tech level 15: Most infantry is by now equipped with battle dress and has converted to the FGMP-14. The gauss rifle remains the standard arm of non-powered troops.
FGMP - for when collateral damage is a feature, not a bug.
Exactly. Yet improving weapon technology tends (within a given weapon type) to reduce collateral damage.
One of my favourite moments form the CT short Argon Gambit.After the first round of gunfire, however, a bright flash of light will
literally burn them from behind. The two men who burned them will show themselves
briefly to check the bodies, and then leave. These unknown protectors are
armed with FGMP-15s