i have an early 80's 870 wingmaster. want to convert to home defense gun. am looking for an 18in. barrel chambered for 2 3/4in. shells. went local gun shop and tried to fit an 18in. barrel of a current 870. won't fit. just a hair too long. couldn't get the magazine cap on all the way.apperantly the current barrel is chambered for 3 in. mag shells and won't fit my receiver. anyone who can help please contact me. thanks in advance, michael