Hayst,

FYI here is a 3-6 that was made the same time as your sheath (Very early 60's). Note the big difference in choil cuts vs your late 60's knife:



Here are a few more sheaths with those same snaps:



One of the above sheaths has the Heiser mark. The other is not marked at all:









Here is that same snap on a Heiser cartridge carrier:





It was pretty close to a decade after the first brown button outage in the very early 50's that it happened a second time.

Ron