The barrel itself is not really the issue, some people think, yup, it's clean, based off the barrel appearance, but, it's in the depths of the chamber where you can't see good unless you have a borescope to peek in there. I usually scrub it for a few minutes, then flush it out, then repeat, and then it's fun time, take it and try it, see how it does.
Also, you can really clean the guts of the big end of the gas tube with the .410 brush and solvent too, this is another area that could also be a contributing cause to weak ejection, I threw this out there because it's just another place to check and look, and another place thats frequently ignored. The small end, an old .22 brush works on. Old grease in it's depths can hamper or slow the gas system down.
After this, you will then know if it really has a problem, hopefully it doesn't, but, we just need to eliminate the previous user/abuser from the picture...makes troubleshooting a little easier when the rifle guts are truly clean.