In order to effect a better understanding of the dimensions and conditions critical to reliable feeding in the 1911 pistol, I thought this might be a good idea to go into more detail than the average magazine article.
The first critical spec is feed and barrel ramp angles. The feed ramp is ideally 31-31.5 degrees and no less than .300 inch deep in the frame measured from the rails, though many old GI pistols did fine with .280 inch. Many custom builders go much deeper, but I’ve never found it necessary with magazines that don’t promote nose-diving. The top corner of the ramp should be sharp and clean and well defined. This is where many people get in trouble with polishing. If the top corner is “rolled” or rounded even slightly, it causes problems about as often as not by sending the bullet nose straight into the barrel ramp.
The barrel ramp isn’t a guide. It’s a clearance, In a correctly functioning pistol, the bullet nose shouldn’t touch the barrel ramp below the top corner as the cartridge glides across it and breaks over, or…at most…lightly brush it as it climbs toward the chamber. This is critical in positively holding the barrel down on the frame bed.
The barrel ramp should be 31-32 degrees with a light rounding at the top corner permitted. The bottom of the barrel ramp must not sit flush with the top corner of the frame ramp. It should properly sit .032-.035 inch forward. A little more is okay, but no less than .032 inch. If this condition is present, no polishing beyond seeing that the ramp is smooth and free of burrs is necessary.
All this is aimed at holding the barrel in place until the cartridge is nearly horizontal and well into the chamber with the rim under the extractor. The barrel should not move until it makes contact with the slide breechface. If the barrel moves forward and up too early for the lugs to engage with the slide’s lugs smoothly and without interference, an intermittent feedway stoppage is virtually guaranteed.
The 1911 was designed around the controlled feed principle. That is, the cartridge must remain captive from the magazine to the chamber. One problem with many modern parallel-lipped magazines with the familiar timed release point is that they release the round too early and too abruptly. If the gun loses full control of the cartridge at any point…even for a very short instant…the opportunity for a stoppage is present.
Since the slide moves at fairly high speed, its dimensions are absolutely critical in maintaining full control. One dimension that so many fail to consider or even know about is the angle of the breechface itself. Assumed to be dead on at 90 degrees, it isn’t. Print specs call for 89 degrees, 8 minutes with no toerance given. ANyone who understands machining knows that the smaller the tolerance, the more critical the dimension, and this is the only dimension I’ve ever seen on a blueprint that provides no tolerance. This tells the machinist that it must be adhered to within tenths of thousandths of an inch and hundredths of a degree.
This very slight departure from what appears to be 90 degrees is to maintain contact between case rim and breechface when the cartridge reaches the final release point….when it fairly “jumps” the last bit to get fully under the extractor’s control. It was actually one of Browning’s redundancies to keep the round from getting loose should the magazine release it a little too early due to feed lip damage or dimensional variation.
The two small, rectangular guide blocks on the underside of the breechface…the extractor passes through one of them…are correctly between .482 and .486 inch apart with .484 being ideal, and the distance that I always worked for when the distance was narrower. I can work with .486, but any wider than that made fitting and adjusting the extractors more problematical. Not impossible, but less forgiving.