Both Springfield Armory and Winchester manufactured narrow and wide base gas cylinders during World War II. The wide bas gas cylinder was developed so that rifle rejection rates would go down. With no latitude to adjust the front sight for windage, it was easy for rifles to not meet the required specifications. The adoption of the wider platform, for the front sight, allowed the Armories to adjust the sight for windage. It is easy to determine which gas cylinder you have by looking at the width of the sight platform compared to the width of the front sight.