I previously posted a feeding problem I was having with my alloy framed SA 1911. I went to the range today and was able to see it happen again and checked to see if some of the questions I was asked were answered correctly.
Discription: On the last round in the mag the slide would lock back (Yes it actualy locked back) while the round was sitting loose on top of the mag but out of it. The round was not in the chamber of the barrel but free floating on top of the mag.

  I isolated it to a specific mag (mitchel 8rder from cddn) I brought a long some new Novaks and they fed every thing without a hitch. I think what was happening is somehow the bullet was nose diving and actualy bounced out of the mag but I do not know. Any way the Novaks seem to have taken care of the problem. I am going to get some more Novaks and some conversion kits from tripp industries for my two shooting stars and mithchel mags. I have the barrel that has the feed ramp built into it unlike the standard 1911 and I guess it does not like normal mag followers. My SA factory 7rders work ok but I noticed their followers are a bit different than my shooting stars or mitchels and do not nose dive as easy.

I posted this because Hobbs5624 was a great help to me and wanted to know what I came up with so I wanted to post the next time I was able to shoot that particular 1911.
Thanks for your help Hobbs 5624 and other posters that was trying to help me figure out why my pistol would do this. I still am not sure what was going on but I know it does not do it the Novak mags.

The SA mags have the dimple followers. These are very good mags. I bought ten with my loaded coupons, and the follower are made to JMB specs. All I did to them is ad a 11# Wolff spring. These Mags have been 100% reliable, More reliable the McCormicks Power Mags and the Wilsons 47D's Well anyway the dimple followers help control feeding of the last round. I cant really explain how it works. I just know the dimple followers are the best followers for the 1911.I have change the followers in my McCormick to the dimple followers and I have not one problem with it.

Two things come to mind,

One the recoil spring is on the way out or underpowdered, and casing a higher than normal slide impact off the frame which is dancing the top round out of the mag.

The second is that the mag springs are too weak, and the last round is getting danced.  As noted, the S/A 7 round followers have the dimples, but the steel follower is less than idea when cut down for the 8 round count.  On my S/A converted to 8 round mags, I use the wilson 47D followers/ spring kits and have have been good luck with them (keep in mind that my pistols are all recoil sprung to eject the cases to 5 feet  per ammo that is being shot, so that greater than needed last round follow tension really doesn't come into play).

The recoil spring has about 600-700rounds on it.

I change them every 2500 rounds. No matter what semi I use. they're cheap enough to replace frequently.

Quoted: Two things come to mind, One the recoil spring is on the way out or underpowdered, and casing a higher than normal slide impact off the frame which is dancing the top round out of the mag. The second is that the mag springs are too weak, and the last round is getting danced.  As noted, the S/A 7 round followers have the dimples, but the steel follower is less than idea when cut down for the 8 round count.  On my S/A converted to 8 round mags, I use the wilson 47D followers/ spring kits and have have been good luck with them (keep in mind that my pistols are all recoil sprung to eject the cases to 5 feet  per ammo that is being shot, so that greater than needed last round follow tension really doesn't come into play).

+1

You know even for an alloy frame the recoil does seem very stiff. I think I will order a new spring when I get my 92 and witness springs. What would be a good weight for a wolff spring in my SA 1911?

Though I'm a 16.5lb person, try an 18.  If you look at the Wolff website, it has a good explanation of what should be in the gun.  

Thanks for the info guys.

FYI, on the 92/M-9, your going to find the pistol cycles a hell of lot cleaner using 15 LB recoil spring instead of the factory 13 LB units with standard 9mm ball ammo (the 15lb may be too strong for weak reloads though).  With the 15 lb spring the cases are ejected about 5-8 feet, instead of the over your shoulder into the next county that the factory spring seems to offer.