At the Las Vegas show several years ago, I tested one sample of Lippard's gun with one-piece barrels and found them to be of typical weight, balance, and MOI. I did not test them for regulation.
I'd surmise thw main factors on current level of acceptance. One, they are still costly relative to current maker's product cost. And, two, makers and their customers still have a lot of inertia in the direction of current current barrel assembly practice. I'm sure one-piece barrels will come, I'm just not sure when.
No one has mentioned yet that one-piece barrels appear very limited in repairability. Of course, if they become cheap enough, that would be a mote point.
