In the 1950's, BSA made a Muzzle Brake available on their CF bolt action rifles they mfg'd called the BESA.
As I recall, the brake was machined right into the bbl itself and not an add-on feature.
The front sight ramp was in place right on top of where the slots were cut out at the sides of the bbl.
No Markings that I know of to tell you that you had a special BESA on your rifle,,you just had to know that.
They were extremely loud in use,,muzzle brakes can be that way. But so much so that BSA offered a metal sleeve device that slipped down over the muzzle and down as far as to cover the ports.
It was open along the top to pass by the front sight ramp.
A lug on either side projected upwards just far enough to allow a small screw to pass and clamp the sleeve in place.
Maybe a former BESA owner disliked the devise so much that they had it cut from the bbl. The front sight ramp moved back and bbl recrowned.
Never to throw anything away, a gunsmith kept it and later found use for it with another customer that delighted in reducing the recoil of his M70.
Some internal threads into the cut off BESA and matching male threads on the M70.....
Well that's my story book tale.,
As far as other Muzzle Brakes,,Herters sold one in the 50's and 60's to be gunsmith installed on your rifle.
Needed your guns bbl to be threaded.
The brake had a single slanted vent on the top of the brake IIRC. Maybe they made other styles too.
Added,,,
Here's a pic of a Herters muzzle brake,,it has 2 vents on top,,not the one I had remembered.
https://www.worthpoint.com/worthopedia/herters-recoil-eliminator-muzzle-137703612
