The new bullets are Hornady 200 grain LSWCs. They often fail to feed with the action closing on a cartridge sitting nose up at a 45 degree angle. I noticed that the new bullets are stubbier than the old ones. Changing the seating depth hasn't helped. Cabela's stocks Berry's Preferred Plated Pistol Bullets, anything from 185 to 230 grains in various shapes. They aren't quite as cheap as the LSWCs but the round nosed ones should feed more reliably.
Have you checked your magazine springs? More importantly, have you ever replaced your magazine springs? (And your recoil spring, as someone else said?)
Without seeing the issue, it SOUNDS like a combination of mag spring not pushing the top bullet into the right position in time for the slide, AND the slide not having enough umph to drive it forward anyway. (Which, I'll note, is a perennial problem with many 1911s. Finding magazines that are reliable with a particular firearm is....an issue. And then keeping them running is another issue.)
When the bullet is stopped, is the case contacting the throat? Or the bullet itself?
(How much crimp are you putting on the case at the end? Is it still flared slightly?)
Note: Some 1911s just don't like some bullet shapes, and won't feed them. It really might just be that. But...springs are often the culprit for many issues.
Are there any problems with plated bullets? I have been told by one person that the plating comes off and fouls the barrel. Note that I load to around 800 fps to minimize recoil. I don't know what his velocities were.
As SFG said, you have to be driving plated bullets pretty briskly to have issues with the plating, and in .45, you simply aren't going to see it at all. No problems there.
My other problem is a frequent failure to ignite with the new Winchester primers. They are not hangfires that go off if I wait a bit. So far I have been able to get all the failures to fire after a second or third strike. Because of these problems I have been using factory 230 grain round nose FMJ ammunition in matches. With that ammunition, every cartridge fires on the first strike. Since the problem appeared when I began using the new primers, I am inclined to blame them rather than the gun especially since it is reliable with factory ammuntion. I wonder if Winchester primers are harder now than they were thirty years ago. Would it help to switch to a different brand of primer? If so, which one?
I use Winchester primers pretty much exclusively. It would surprise me extremely to find that they are harder to ignite and would cause this sort of problem. Sure, it might be from a bad lot, but...since you are only having problems with your reloads, and not
factory ammunition with the same primers, my guess would be something about the primer depth is an issue---particularly since you can get them to light on the second strike. First strike is light due to high primers, but it drives the primer down a bit, second strike lights them off just fine....this is pretty common.
Doesn't mean that IS the problem, but I'd certainly check that out.
Federal primers are pretty much the softest out there, if you need to switch.
Do you check for high primers at the end of the reloading process? How deeply do you seat your primers?