You are correct that some will take issue with this and you are not correct on why as this is not what the law says. ....
Regardless of design, it is still an M/L.
Really it doesn’t mater if they take issue or not , its fact
What I was getting at is that some of the early plunger type inline ignition guns are simply reproductions of pre 1898 rifles that have modern stock designs , nothing less nothing more
As to the 2nd part , Ill have to disagree .
Infact as I said , its easily looked up on the ATF web site .
While most that require FFL’s are systems with interchangeable barrels , not all are . Just because it loads from the muzzle doesn’t mean it doesn’t take an FFL .
It also has to do with the design of the action and receiver making it “CAPABLE” . Case in point , the Knight ML10 .
The original design failed the letter of the law and was found to be “capable” of converting to center fire . Knight had to redesign it slightly . IE they removed one of t locking lugs . It then passed the ATF checks and now the 2nd model is sold without an FFL even though its smokeless .
In fact the ATF specifically lists the ML10 “1st version” as requiring a FFL on their web site
Now if we look at say the Bad Bull , it requires and FFL
Here is the actual laws as its written