By the proofmarks, that gun was made between 1925-54. If you look at those H&H shotshell boxes--and I happen to have a box of 67mm 16's from H&H--it will likely tell you that they're OK if the gun is proofed for loads of at least 1 oz and the chambers are at least 2 1/2" in length. Your gun is good to go in both those areas.