Enough familiarity with his firearm that he can clear FTF/FTE without hesitation, not enough time to familiarize himself with suppressor mechanics and effect on handgun cycling. I wouldn’t be overly surprised if this was a recent form 4 registration.
That’s wild, I didn’t even know that was a thing. I wonder if he’d have had better luck buying a US-made piston off the shelf and finding an “oil filter” that fits.