Hello,
You have a B-O-Y-L-E (BOYLE) made drum pouch. I found two(2) of them many years ago unissued. I sold one and kept the other, I have probably had it for thirty years, or so. The BOYLE made pouches are not rare, but are not as commonly seen as several other manufacturers. They are are not date marked, but typically these pouches were manufactured in 1942. It is an original WWII military issue pouch for the fifty round drum. Nice find.
The BOYLE Logo is very hard to read and it appears to have been somewhat smeared when applied. The one pictured below is about as clear as they get.