DO NOT shoot that rifle any more!
They are notorious for the receivers breaking due to the age of the material that they were manufactured from.
As it sits, that is a valuable rifle. Once that receiver cracks or breaks, not so much.
Go to the American Vintage Airguns forum, register and post about it over there. It should cause a little bit of a stir.
American Vintage Airguns-
www.tapatalk.com
I do believe that you should receive the opinions of some knowledgeable collectors before shooting it any more. I may be wrong about which model was prone to breakage, but be sure to find out before continuing. I know that the 1925 model was known for receivers breaking apart, and am not absolutely sure that it does not apply to the earlier models as well.
I posted on the AVA forum in the hopes that one of the guys who knows stuff will pop in here and comment on your rifle.
Great example by the way, very nice early rifle, actually the earliest model due to the rear sight mounting.