Print them sure, print them with enough accuracy to actually work with a firearm no. Enough sanding might get the job done but it won’t work reliably for long if at all

Edit: little more explanation, the holes and alignments need to be just right for the trigger group and the slide rails are the hardest parts. They’re fairly small but need to be very smooth and induce very little friction (for a pistol) on a rifle it’s a little different since the moving parts are in the upper sans the trigger group. Even then the threads have to come out pretty darn nice for the buffer tube and accuracy on the mag well especially where the hammer goes is really important. Can it be done? Sure, are you going to have to be a pretty darn good understanding of mechanics to get it done? Absolutely. Now we’re back to someone who has the skill to 3d print a weapon with the current state of technology probably has the skill to do it other more effective ways