I'll break this into two parts to keep it from getting overlong and tedious.
The first thing to understand is that "Controlled Feed" means exactly that. The cartridge must be under control at all times, from the instant it enters the magazine until it's in the chamber. In order to do that, it must remain in forced contact with at least two points.
In order to fully address this, we have to go back to the magazine. Browning's magazine...not McCormick's or Wilsons's. There will be a "thousand words" thing at the bottom of the post.
The original magazine's tapered feed lips accomplishes two things.
1. The taper allows the rear of the cartridge to rise as it moves forward and the front rises on the feed ramp. The release actually starts the instant the round moves. It's a gradual, late release that works to maintain control.
2. The rise at the rear not only reduces the angle of approach to the chamber, it places the rim part way under the extractor before it relinquishes control, so that when the round finally breaks over to horizontal, the extractor already has it, so if the round somehow loses contact with the breechface as it breaks over, the rim has nowhere to go except under the extractor...and control is maintained.
The photograph below shows how the two different feed lip designs affect the feeding of the cartridge. Both are 7 round sticks with the original design followers. The difference is in the feed lips. The one on the left has parallel feed lips with the timed release point. The one on the right is a "hybrid" with the original taper and a later timed release point.
Both cartridges have been pushed forward until the rims contact the follower bump, so both are in the same location. The obvious difference is the positions of the cartridges relative to the top of the magazine. The one on the right is positioned closer to the extractor...actually just starting under it. With the full taper of the original lips, the rim is even higher at final release...almost completely under the extractor...and the angle going into the chamber nearly horizontal.
The first thing to understand is that "Controlled Feed" means exactly that. The cartridge must be under control at all times, from the instant it enters the magazine until it's in the chamber. In order to do that, it must remain in forced contact with at least two points.
In order to fully address this, we have to go back to the magazine. Browning's magazine...not McCormick's or Wilsons's. There will be a "thousand words" thing at the bottom of the post.
The original magazine's tapered feed lips accomplishes two things.
1. The taper allows the rear of the cartridge to rise as it moves forward and the front rises on the feed ramp. The release actually starts the instant the round moves. It's a gradual, late release that works to maintain control.
2. The rise at the rear not only reduces the angle of approach to the chamber, it places the rim part way under the extractor before it relinquishes control, so that when the round finally breaks over to horizontal, the extractor already has it, so if the round somehow loses contact with the breechface as it breaks over, the rim has nowhere to go except under the extractor...and control is maintained.
The photograph below shows how the two different feed lip designs affect the feeding of the cartridge. Both are 7 round sticks with the original design followers. The difference is in the feed lips. The one on the left has parallel feed lips with the timed release point. The one on the right is a "hybrid" with the original taper and a later timed release point.
Both cartridges have been pushed forward until the rims contact the follower bump, so both are in the same location. The obvious difference is the positions of the cartridges relative to the top of the magazine. The one on the right is positioned closer to the extractor...actually just starting under it. With the full taper of the original lips, the rim is even higher at final release...almost completely under the extractor...and the angle going into the chamber nearly horizontal.
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