Literalmente, “mazo cargado con granos/perdigones” (shot loaded mallet), pero evidentemente esta traducción literal no es aceptable. Se trata de un mazo muy especial que tiene en su cabezal una especie de cartucho cilíndrico, cargado con bolitas metálicas (= shot), ocasionalmente también otros materiales como arena, que interviene en el impacto dispersando la energía del contacto y evitando así el efecto de rebote. También existe la traducción “mazo o martillo de impacto”, con la que estoy en desacuerdo, ya que todo golpe de mazo o martillo, sea del tipo que sea, conlleva por definición un impacto.

En inglés, “shot loaded mallet/hammer” es sinónimo de “dead blow mallet/hammer”:
https://www.disher.com/2016/07/13/hammer-time-7-common-hamme...
Hammer Time… 7 Common Hammers & When to Use Them
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6. Dead Blow (Heavy Duty – Non Marring)


A dead blow hammer is a solid polymer mallet with a hidden secret. Inside the hammer head is a cylinder filled with lead shot, sand, or steel shot. When the hammer is swung the shot lands dispelling all of the energy into the object being struck. This virtually eliminates any rebound within the hammer’s head, which is a common problem with a standard mallet. The shot delivers a great deal of force per swing without the hammer needing to be very heavy.
Due to the dead blow being made of polymer it is very helpful in minimizing the damage to a struck surface. Therefore, the dead blow is used very similarly to a traditional mallet but for objects which need a little more force in order to move. Dead blows are great at dislodging stuck parts, driving stiff wooden joints together, or to pop small dents out of sheet metal. This hammer is also ideal for striking objects with a great amount of controlled force such as chisels and other sharp objects. This allows for more aggressive cuts without damaging the chisel.

https://en.wikipedia.org/wiki/Dead_blow_hammer
Dead blow hammer
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Description
The head of the dead blow hammer can be solid or hollow (often partially filled with loose steel shot), which distributes the energy of the strike over a longer period of time and reduces rebound.

https://quesignificado.org/que-son-los-martillos-de-impacto/
¿Qué son los martillos de impacto?
Los martillos de golpe muerto son martillos con un diseño único cuyo objetivo es concentrar la fuerza de un golpe y reducir el efecto de rebote que experimentan las personas con los martillos normales.
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La característica clave de un martillo de golpe muerto es que la cabeza del martillo es hueca y está llena de un material como arena o perdigones.



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Note added at 1 hr (2022-08-06 09:46:24 GMT)
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https://www.sailrite.com/Dead-Blow-Hammer-3
Description
Dead Blow Hammer 3# is a shot loaded hammer that transfers the force of the blow directly to the work. This Dead Blow Hammer has a rubber head to prevent sparking and won’t mar your work. Excellent for use with grommet die sets, hole cutters, rivet settings, soft metals and auto bodywork. Additionally, the Dead Blow Hammer can be used for nailing metal tack strips and other upholstery items.