Never owning one you're just talking from hear/say with no personal experience. That's called a rumor. Rumors aren't worth squat. I, personally, own a couple and have vented, tuned and proofed many. I've run into a few made in someone's garage in India with a water pipe for a barrel. However, India guns made by established manufacturers, are decent guns and work as designed. Semper Fi.I’ve never met one in person that was of sufficient quality to justify me parting ways with my hard earned money. I learned all too well from my financially irresponsible father.
Here's a pic of my 1717 French Military Musket from Military Heritage. I've fine-tuned it so the trigger pull is decent. .69 cal. I get 6" group at 100 yards. .680 ball, .010 oiled patch with .75gr 2F Goex. I have lots of Goex.