The ARMSCOR model 20 was made for quite a few "Big Box" stores, like K-Mart, and was rollstamped with the name of the store, or S-B, or ARMSCOR, or any two of the three.
Squires-Bingham was the original 1905 British Factory which was run by the Tuason family since 1952...and in 1980 changed the name to ARMSCOR.
In the last decade they've invested heavily in CNC equipment and have been turning out a better line of products than ever before!
Your model 20, currently known as the M20P (Model 20 Plain) or M20D (D for Deluxe checkering) or M20C (C for Carbine, shorter barrel and barrel band).
It should be easy to tell which version you have, especially if you post a pic
Here's the manual...
Special Note: Phillipine Mahogany or Phillipine Wood...
This is more commonly known as Rubberwood...as in, the tree they tap for rubber like you do a Maple tree for Maple Syrup.
If you ever refinish a stock of this material...DO NOT USE MINWAX STAIN!! The rubber sap will not allow a smooth finish.
You will need to use a HIGHER GRADE of stain than cheap Minwax...like Formby's, General Finishes, Old Dad's...etc...
As far as clearcoats, Minwax Polyurethanes & other clearcoats are fine after using a High Quality Stain. I'm fond of their Spar Urethane (Marine Grade Poly)
It also does take paint very well if given a light sanding first.
Hope that helps