The notch for the catch being triangular identifies it as Savage, Remington's are rectangular. File the notch out & it will fit a Remington. It was used in almost all Savage and Stevens box magazine rifles rifles for a number of years staring in the 1930's. There were two different size 5 round and a 10 round. Yours is the longer five round and will fit any rifle, the shorter 5 round will not fit in rifles with heavy contour stock like the Savage 23-AA & 19-33 or the Stevens 416.
CORRECTION, I originally had this wrong, now corrected - The top of the notch in a Remington is NOT in the same location as the Savage, Remington magazines will fit a Savage BUT WILL NOT ENGAGE THE CATCH.
Last edited by GeneB; 01/10/21. Reason: corrected error
CORRECTION ----- this answer to that post is wrong-> They're more than just similar, like I said, file the notches for the catch out and it will fit a Remington and the Remington's will fit a Savage without modification. correction ->New notches need to be added to a Remington to work in a Savage, I've had one in a Savage I bought sometime ago and didn't realize it was just being held by friction, sorry for not looking closer to begin with and making a wrong assumption.
Attached a picture (.....what I should have done at to begin with, sorry for the (my) confusion) -
According to Triple-K the Remington Nylon 11, 511 & 513 all took the same magazine. These Savage & Stevens models all took the same with the shorter version not fitting the heavy stocked guns - Savage models 4, 7, 1933NRA, & 23-AA; Stevens models 56, 57, 84, 85 & 416. They also list some models of Anschutz but I'm not sure about the earlier magazines working in them, I think the later ones with a second set of notches higher up are for those, like the short one pictured (another assumption... but I've been wrong before doing that...)