Antimatter powered laser?

so I'm trying to make a hard sci fi universe. that feels grungy and a bit anachronistic so it's an interstellar civilisation but people still look the same as folks now, there's no holograms, very little touch screen devices, and no sort of internet analogue. obviously theres stuff like interstellar travel (stl), spin gravity, extremely long ships with radiators, space habitats, and some future weapons like particle beam weopons, lasers, rail guns on attack ships. want it to feel like its a bit old and a little dirty.

in line with this I originally wanted to keep the characters using modern chemical weapons but I still thought that might seem a bit too anachronistic since the setting still takes place at least 20k years in the future so I thought up another weapon.

what I was thinking was there is a small penning trap (like the size of a shotgun shell) made of a room temperature and pressure stable superconducting metallic hydrogen that contained a very very very very miniscule amount of antimatter and when the weapon is fired the antimatter meets normal matter and is annihilated producing gamma rays which are absorbed by the metallic hydrogen breaking it down and turning it into plasma and making it release reflectable photons and (OK going forward from here I'm a bit less sure on the science here but) the plasma is used as a lasing medium and the photons produced are reflected and columnated to create a high energy laser all this is meant to happen fairly quickly like as fast/faster than human perception and (this one might change) the hydrogen us ejected forward after everything to make space and to give the weapon recoil (that last bit bout the recoil is just for the aesthetic so its open to change).

these would come in a variety of forms and the penning trap would act like and be stored like bullet.

I'm curious as to if any of this is really plausible or just technobable but it allows my characters to have weopons that feel high tech buy still feel like modern guns more so than a typical sci fi blaster.