A couple of observations:
1) The material used to make this part is 6061 aluminum with a .250 bore- meaning it must have been made to only withstand the pressures of
rimfire ammunition. By the time the
rimfire round passes through the third of forth section, most of the gasses have already exited the brake. This is one technique authorities could have used to surmise that the item for sale on eBay was intended to be used in a silencer part and not a muzzle device.
2) The seller could have privately advertised that this part would work as a monocore baffle stack, complete with barrel threads and bore. Remember, manufacturing any silencer parts requires a federal firearms manufacturing license.
3) Stating that a
muzzle brake has a “nice low tone” isn’t exactly evidence, but it also isn’t helpful to the defendant’s case. I don’t recall ever reading about muzzle brakeschanging to tone of a discharged firearm.
4) The defendant has a prior conviction for manufacturing “silencer kits” for which he was currently on probation. Which means if he didn’t understand that the NFA and silencer laws and regulations were complicated before, he should have definitely made time to understand the laws after he plead guilty.