Gents, thanks for your responses and information.
And thanks to PeteM for putting up my pics.
Still working on the meaning of the suspected barrel maker's logo - BTP, which may be within a circle - the strike was faint and on a curved surface.
It's also possible that all the Tobin barrels from this maker showed this mark, but the marks was struck off when the tubes were finished up in Norwich or Woodstock. I suspect G.B. Crandall assembled this particular shotgun in the 1920-30s, and really did not care if the barrel maker's mark was completely erased or not. Due to the faintness of the logo, it might have been missed. I missed it during my manual inspection and only noticed it when reviewing the pics I took.
Thank you all.
