1899 Takedown 22 HP threaded muzzle

I have a Savage 1899 takedown in 22 High Power made in 1913.
The muzzle is threaded and on the bottom of the barrel below the front sight there is a small notch.

The threading I would assume is for a suppressor. what is the notch for?
Was this done by a gunsmith after the gun was purchased or was this a factory option?

I have owned it for many years but never fired it. Brought to the range and it supprized me how accurate it shot.
With handloads at 50 yards Iron sights a 7 round group measured 1.2 inches.

https://ibb.co/cLaVTx
https://ibb.co/gbGR1H
https://ibb.co/i5MtgH
https://ibb.co/fCVVTx
https://ibb.co/hz4UMH

I'm thinking it's some sort of muzzle protector to keep the crown from getting dinged up.
OR, some sort of optional front sight, but the current sight base looks brazed on.

Ya see something new every day!! It's got me stumped!!

https://laststandonzombieisland.file...e-compared.jpg

The top picture is of a Model 1910 suppressor fitted to a 1903 Springfield, so it's from the same era as your 1899. It appears to be threaded on with a cross pin, the notch on the bottom of the barrel, to hold it in place. Just speculation of course, but a good possibility!!

I've seen a handfull of them threaded like that in the past, not sure if it was factory or not, seem to be a few out there so I'm always wondering if there was a gunsmith who did a bunch of them and resold them or what the deal was.

That image of the 1910 suppressor appears to be a similar layout to what is on the barrel on my 1899.
I am not really sure but a long time ago an old timer told me he remembers a savage branded suppressor so it may be possible that at least some may have come from the factory threaded.

I've never ran into a Savage branded suppressor but would love to know if they're out there, that would explain all the threaded barrels.