I know that each semi-auto brand and model and even each sample of semi-auto can have variations in reliability with any given load, but I'd like to learn some from your experiences as to what loads cycle with utter reliably in your semi-auto and what loads DON'T.  

Would you share your experiences?  Also mention what model of shotgun, any modifications made to it, etc.? Thanks, in advance.

Dude,
There are just way to many makes of semi's to even think about, much less write novels on their load preferences.

If you want to narrow the field down to a few makes, list them and what you are going to using the shotgun for, and we can help you decide on the model best suited for you.

Estate 2-3/4 Gameloads wouldn't cycle for shit through my Saiga 20, while Winchester AAs cycled without fail.

Dano... good suggestion, fair enough... sorry for being so general. h
Here's what I've got so far with a brand new 1100CM:

As expected, 00 Buck runs like a top in the new gun.

But being brand spankin' new, I expected some cycling issues with light ammo and I got them...

Winchester Super X Game Load 2.75", 3.25 Dr Eq, 1 oz., #6

will not cycle AT ALL.  Not a big surprise... I was told to expect this, at least initially, with 1 oz. loads, due to the stiffness of the new recoil spring.

A subsequent test with:

Estate Heavy Game Load 2.75", 3.25 Dr Eq, 1 1/8 oz., #6 shot shells

proved smooth and totally reliable. Wham bam just right every time. Amazing what a difference just 1/8 of an ounce will make!

Then:

Estate Super Sport Competition Target Load 2.75", 3 Dr Eq, 1 1/8 oz., #7 1/2 shot shells

cycled 5 of 6 shells, but one of them didn't quite push the bolt far enough back to eject the shell.

It seems the new gun wants 3 1/4 Dr Eq and 1 1/8 oz. to cycle reliably at this time.

A follow up with another 8 shells of:

Estate Heavy Game Load 2.75", 3.25 Dr Eq, 1 1/8 oz., #6 shot shells

flew in and out of the shotgun as fast as I could pull the trigger... WHAT FUN! Oh man... I feel like a kid in a candy store.  Semi-auto shotguns are waaaay more fun than I had any idea they would be!!! (Can't wait to get my hands on the FN SLP I've got coming next week).

As has been suggested on Brian Enos' 3-gun forums, for a week or two I will store the new 1100CM with the bolt locked back to soften the recoil spring tension a little. And to help "wear-in" the gun, I'll be pushing a lot of the aforementioned Estate Heavy Game loads through the gun.  So far, I'm really liking this shotgun!

And I've got to get some slugs to test too.

I don't expect I'll be taking this shotgun into any 3-gun competition until next spring, so there will be plenty of time to thoroughly wear it in and test it out in the laundry room. (I use stacked fir rounds as a backstop, but unfortunately, shotgun blasts sure chew through that wood quickly... got plenty of sawdust!) I'm going to mix in lots of outdoor shooting as well.
;)

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UPDATE.... after firing the gun some more tonight, interestingly, now the Estate Super Sport Comp load that was just a little balky is running through the gun like greased lightning... I had read that new semi-auto shotguns take some wearing in to run really well, and I'm experiencing that... it does just get better!

Benelli super 90 feeds everything fine now. When it was new it would not cycle light target loads. After a few thousand rouns light loads cyle 100%.

My Beretta AL390 cycles most anything. I shoot clays with it quite a bit so those are 1-1/8 oz 1200 fps load which are quite mild compared to home defense loads.

I'm not real familar with the newer AL391 but the old 390s you could use different valve springs in them if you wanted to tune it. I never bothered doing that.

Sounds like I just need to shoot the snot out of this new 1100CM and then try some really light stuff to see how it runs.  It's comforting, at least, to know that the heavier loads, even the medium loads run like a top in it.

I have a Bennelli M-3.  (pump/auto).  It has only had maybe 200 rounds through it.

Shooting Federal reduced recoil 00 buck.  It often chokes at or after the third round with a rapid dump.  That disappoints me only becaue I have a bunch of that stuff.  I usually shoot only full power loads... so since I have a bunch of this... it is disappointing.  Maybe after a few hundred rounds the M-3 might break in a bit and do OK.  I like hot loads better.

My Benelli shoots the reduced recoil loads like butter.  It does well with 6 or 8 shot as well.

I have not tried messing with ultra-light loads, as my Benelli is a big gam getter not