Unless you’re content using 22LR, fully DIY 3D printed self-loading handguns just aren’t currently viable. Even those in 22LR are challenging builds with questionable reliability. If you want a reliable DIY semi-auto, you’re going to have to settle for PCC/PDW platforms. Even with those, the barrel is a bit of a barrier. DIY is possible, but you’ll have to master the electro-chemical machining (ECM) process. Barrel liner builds are only realistic for 22LR due to the enormous pressures involved in center-fire handgun ammunition. But note that in the US, commercial barrels aren’t regulated. Any local gun shop will be happy to sell you one in a cash transaction with no paper trail.

That said, relying on a 3D printed firearm for personal protection is questionable at best. Unless you’re legally restricted, pick up a law enforcement trade-in 9mm handgun or a pump-action shotgun (both can be had for just a little more than the cost of a 3D2A DIY build) and call it a day. Think of 3D printed guns much as you would a “curio and relic” antique. Cool to own and maybe safe to use it at the range, but not something you bet your life on. I love my Urutau, but it’s had one OOB that destroyed half the gun and the rebuild is now on its third firing pin. Lately it’s been running good and will shoot a full mag without a failure, but I also know that the chance of something breaking or wearing out on the next shot is orders of magnitude higher than even many antiques.