Here is a concept I made. 23rds. This one can also load on a closed bolt, activate the last round bolt hold open and doesn’t bust like a melon or damage the internal sprocket if dropped fully loaded let alone empty. The pic makes it look like the tower area is longer but it does fit flush to the magwell...
I was totally scratching my head the first time I saw the 25rd drum. Crazy how much bigger it is for just 2 more rounds. A perfect example on the difference design can make in a product...