squirrelgirl-
Several things could be causing your problem, and with an 1100, they are usually simple fixes. I would recommend, if your gunsmith cannot fix an 1100, try a different smith.
1. Field strip the weapon by removing the magazine tube nut under the barrel, and remove the fore end and barrel. There are two holes inside the round lug that goes around the magazine tube. Make sure these are not obstructed. Clean with a paper clip, or pipe cleaner. If there is only one hole, your barrel is a magnum model, and may not shoot lighter loads well.
2. After cleaning the gas port holes, look at the chamber end of the barrel. About 3/8" from the end, there should be a small stub protruding about 3/16" or 1/4". This is the ejector, and if damaged, or missing, your gun will not kick out the shell. Any competent gunsmith can replace this.
3. Next, look on the magazine tube, and find the rubber O-ring and the metal gas checks. On older models, there will be a two piece gas check. On newer models, the gas check is one piece. Make sure your O-ring is not damaged, and the gas checks are installed correctly. There should be a small diagram depicting correct installation on the underside of the sliding part that is around the magazine tube.
4. With the gun disassembled, check the extractor. This is the small part you can see on the bolt, through the ejection port. The extractor should be spring loaded into the bolt,(just a little wiggle) and have a good, defined edge to fit over the rim of the shotgun shell. If it is broken or rough, the extractor cannot pull the shell from the chamber. Have it replaced.
5. Thoroughly clean the chamber. This is the first 2 3/4" or 3" of the barrel. Sometimes powder residue, crud and even rust can hold back a hull enough to inhibit good extraction.
If none of these basic fixes will work, I would recommend finding a different gunsmith, and request that he fire the weapon to determine the cause of the malfunction.
Hope some of this will help, and good luck!
crm

This is not uncommon problem with 1100's. I f you have never done this before, make sure to do it inside the house to prevent missing parts Carefully remove the top of the gas cylinder, the spring may fly out like a champagne cork. This stopper is right ahead of the forearm. Keep your head away and your hand on top. Once you have relocated all the parts, clean them carefully with brake cleaner, or something similar. This is also where the plug goes that limits how many rounds you may use legally to hunt with.
You should probably to take it to a gunsmith the first time, don't forget to duck.

that is a common problem with 1100 ive had over half a dozen, after a good cleaning most of them seem to work better but i have 2 at the moment that refuses to shoot anything but high brass shells, no matter how much cleaning and oiling i do. try cleaning the gas holes on the barrel, the wholes are located where the barrel slides over the magazine tube. pipe cleaners work great for that.

Don't know if this is the case with yours, but my older 1100 had a power ring on the top of the magazine tube that you had to invert if you were shooting magnum loads. If you tried to shoot regular 2 3/4 shells, it would not load. I would expect that your gunsmith would know this and position it appropriately but you never know. Friction of that ring on top of the magazine tube has major impact on reloading.

Tell us what it is doing.is it pulling the fired hulls from the barrel completely,or is it not releasing a fresh round into the chamber,is it full cycling and locking on an open bore.Give us some help.

i used to use an 1100 20 guage. Try higher end brands. Clean often. It usually likes bigger shells like slugs,steel,bigger birdshot

low brass shells cause the same problem for me,are you shooting high ,low,or mixing rounds?

I have an 1100 in 20 gauge and I was having the same problem. I found 2 simple issues. #1 was low base shells didnt have enough weight to kick out completely. I switched to hi base and no more problem, UNTIL, after several hours and many many rounds of practice, the powder build up and whatever dirt and grime in the chamber seemed to cause the same issue even using hi base. For me, using hi base in the field(not so many rounds in a day) didnt have an issue. So try using hi base and keeping everything clean and you should be good to go. happy huntin'