Safe for the target, also maybe. Just depends on whether the exploding action and barrel throw shrapnel down range, or if you had a shitty weld. Guy holding it won't have a good day, but could survive. Something something Kentucky ballistics.
Read somewhere in an book that sometimes soldiers/aides tried to hurt/kill their officers my minimally reducing their barrel width mechanically when cleaning their pistols for them.
Hard to detect and can fuck someone up good.
But while I can see how that would work in theory I don't see how this could be done without someone noticing it and with the tools at their disposal.