I purchased one of the newer Olympic Arms .45 ACP upper assemblies, and the first session of shooting it, after about twenty rounds, it would not feed.  The bolt would get the round most of the way into the chamber and then not be able to get it any further in.  I use a Lee factory crimp die on everything I handload, so I'm pretty sure the rounds weren't too wide.  Having perused the forum here, I saw that many people recommended a heavier buffer and maybe a heavier buffer spring.  I decided to go with the heavier buffer, thinking it was more likely a momentum issue than an energy issue.
So, I purchased a Spike's Tactical heavy buffer.  Went to the range, annoyingly without my magazine, and decided I would sight the red dot in with manually fed rounds, since that shouldn't take more than nine or ten rounds.  The first round, I didn't notice any problems with.  But the second and third were caught between the bolt and the chamber.  I opted to stop there.
The load isn't starting load, in fact, it's closer to max load than minimum, so it shouldn't be the ammunition.  I can't imagine the lack of magazine would be the problem, either.  Was I wrong to go with a heavy buffer?  Should I have just tried to break the gun in more?

I'm kinda going to be speaking Apples and Oranges here. I have a 45 acp upper from Ron Williams.
10.5" with a 5.5" flash hider welded on. It's a design that works, Ron has more that runs great.
It's gas operated. Initially, I was using a standard buffer and spring with a Full Auto Carrier. The upper
would cycle the first round after dropping the charging handle on it. Every round had to be fed individually
after that because the bolt wasn't cycling far enough to catch the hammer and pick up the next round.

Ron opened the gas port more than initially was done, I went to a Colt Horseshoe Carrier and will be
testing it and a number of magazines that I've made from various donors. I'm taking a buffer with the
weights removed and possibly something to cut the spring if needed. I'm running Winchester White Box,
Remington and Federal 230 gr ball. As with mine, you may have too much mass weight. It wouldn't hurt
to try a lighter buffer and or spring. I do realize we are on 2 different operating systems, yours is blow back
and mine is gas operated. But, those are my thoughts.

Good Luck,
Spec

I guess it makes sense, sort of, that since the heavier buffer was worse, lighter might be better.  
As fate would have it, I do have a spare buffer.  The guy I originally asked to get me a heavy buffer got me a standard buffer (or, rather, a buffer that, according to my scale, is 8 grains heavier than the one I had in my buffer tube to start with).  I might try disassembling the spare and removing some weight.  Do you, or anyone, have a suggestion as to how much lighter to make it?  I'd rather not do too much trial and error, even with the $3/hr shooting range I go to.  Otherwise, I'd just lighten it until it works.

It's just one of those things, You need to lighten it a little at a time until it works.
I can't venture a guess on how much since our 45's are so different.
Spec

Oly's .45 upper were designed to be used with a standard AR15 buffer.

What lower are you using? What mags are you using? The heavy buffers are necessary for use with Cav Arms polymer lowers but not necessary for a standard AR aluminum lower. You need to try some basic factory loads like WWB before you do anything else. This sould confirm or deny you have a hand load issue.

It sounds like your chamber was dirty from the loads. What loads were you running?
May also need to polish the chamber. it has come up before. Dont know why oly dosent polish them.
I polish all my chambers to be sure they are as smooth as posible.

SemiChrome Polish comes in a yellow tube with white print and red graphics.
Does wonders to make chambers like a mirror without taking too much material
off. Usually found at Motorcycle Shops or Auto Parts Stores....

I'm so happy that Ron came in with some input. He's the Man.

http://buyitnow64.stores.yahoo.net/simepo.html

Ron: N340 with a plated FMJ.  I've never had to gauge the dirtiness of my loads, so I can't really say how dirty this load is compared to others.  It's never been an issue, even when I owned a Hi-Point.  :P  I sure hope I don't need to polish the chamber.  I hate taking guns apart that far.  Thankfully, however, I do have access to the tools necessary to do it.

Tango: Stag Lower, the newer Olympic .45 ACP magazines (the ones that look like a giant slab of plastic)

I've bought some Winchester white box and my plan is to use my handloads until it stops working again, then switch to the Winchester to see if that helps.  If it doesn't, I'll see how hard it is to just drop a round into the chamber through the ejection port, and it if doesn't go in without help, I'll know it's a problem with the chamber.

Thanks for the help, everyone.

Exelent powder. I run 6.5g N340 & a 230HB. Burn is 99% in my 10.5"DI upper so its not your load. I sugest trying the WWB first(its real dirty) & if it does the same thing I am afraid it is your chamber. I have heard about oly parkerizing the inside of brls & may be why some have to polish the chamber.

My MGI .45 upper wouldn't run until I used the lightest buffer with the heaviest spring.

Well, I took the gun out with standard spring and buffer again, and it works fine now.  Maybe it just wanted some attention.  Who knows?  Apparently the mashed cases from the time I took it without the magazine were because I was dropping the bolt onto a round already in the chamber, and the extractor isn't designed for that.  Dunno why that happens with *this* blowback but not any of my *other* blowbacks.  But, it's an easy problem to deal with, as problems go.

Thanks for all of your input.