Keeping in mind that I retired before the newer 1911's came out and I'm not that familiar with the newer guns, I "believe" this is the newer Colt "dimpled" feed ramp that's supposed to improve feeding of wider hollow point ammo.
Well, I did go to the range today. I had to test a rifle to make a deadline, and wanted to test fire the Defender first. (can't carry a gun that hasn't been tested)
I was actually quite pleased. I began by trying one of our departmental qualification courses. (can't carry it without qualifying w/it either) First try, first rounds out of the barrel, I shot a 95% on the 20rd. course w/ no malfunctions. This was w/ Black Hills' 230gr. JHP.
If you look at the accompanying photo, you'll see that only one round is out of the large scoring ring at 1:00 o'clock. This was one of my weak-side barricade fired from the weak hand at 25yds.
The head shot is a scored shot. (has to be inside the 3" ring)
I then tried several other rounds, and was impressed to find that it even digested the "large mouth bass" Corbon rounds. (185gr. +P) and Hornady 200gr. TAP CQ +P. I fired 230gr. Fed. Hydra Shoks and 230gr. Golden Sabers through it too, all w/ no failures to feed or eject. I finally encountered two failures to feed w/ 230gr. SXTs. I wondered if I'd gotten relaxed and limp-wristed the shots, so I took care to grip the weapon very tightly through the next few magazines of SXTs and had no more failures to feed.
I discovered that one of my two mags does not like to hold the slide open after the last shot sometimes. I marked it, and this will be my "reload" until I get my hands on some more mags.
I'm quite pleased, as I think I got more than my $300.00 worth that I paid for this little gem. That's at least $300.00 worth of performance!
At this point, I think I'll choose to believe the few Defender owners that have told me this is a dimpled barrel and the odd cut is supposed to be there.
BTW: It was hotter than hades out there today! 107 at 51% humidity! I risked my body fluids to bring you guys this report!