I've had the same problem with two different 210's that I've owned over the last few years. In both cases the guns were extremely accurate with Winchester Partition Gold slugs in 2 3/4" size, and slightly less accurate with the 3" version. Both guns were essentially single shot firearms with extra onboard ammo storage, because ejection was not only irregular, it was downright rare! The first gun improved slightly when I switched the one-piece Weaver base that came with it for a two-piece base, but even then I found myself knocking empties out of the open bolt more often than not.
I called Savage customer service for their input, but was only told that the gun was chambered and designed for 3" shells only. The 3" slug loads were slightly less accurate, and slightly more expensive and harder on the shoulder, but they did not eject any better than the shorter loads.
Seriously, look at the ejection port area of the gun, especially with a scope mounted. Then look at a 12-gauge empty hull. I'm sorry, but I just don't believe that is a combination that will ever result in consistent, reliable ejection. It's a shame, because the 210 was a sweet shooting gun that I admired in every other respect. My solution: stop buying 210's. Use my H&R Ultra Slug instead. One accurate single shot with various loads (much less picky than the Savages were) that required only a quick chamber polishing job to deliver consistent, over-the-shoulder-and-into-the-woods ejection every time.
Sorry I couldn't be more helpful.
