I've owned a few 870's, IMO they function fine, however they do have a few quirks. Back in the beginning, Remington made the 870 to shoot 2 3/4 shells. The opening and the extraction/ejection parts worked in harmony. To accommodate 3" shells, (a 2 3/4" receiver will not eject a 3" shell, really bad jamb-up), they moved the ejector spring back a 1/4". Remington did nothing else, the opening in a 2 3/4 receiver is exactly the same size in a 3". As the bolt goes back the 3" receiver just waits that extra 1/4" before it ejects. By setting back the ejector, it allows the 3" shell to just clear the port before it ejects. When you fire a 2 3/4" shell in a 3" receiver, the timing gets a bit weird, the 2 3/4 shell is well clear of the front of the port before it gets ejected. Politely put, a minor design flaw or weakness.
When the 870 was reworked for 3 1/2" shells, it got real ugly looking, I certainly won't buy one.
My 3" Express is set up for geese, I have hunted deer with it, 2 3/4" slugs, ejection was OK, doesn't fling it far, just OK. I have a 2 3/4" Wingmaster as a yard gun, skunks squirrels and other vermin.
If you use 3" shells, and the parts are good, it should eject fine, enjoy. If you want to shoot mostly 2 3/4", find an old Wingmaster with a 2 3/4" receiver. The sn will not end in "M", it will end in "V"
cowpoke on another forum explained it a better:
"There's no difference in the ejection port.
The only difference between 2 3/4" and the 3" receivers is as follows.
The 3" capable guns have an "M" as the last letter in the serial number.
The 3" guns have a longer ejector riveted in the receiver wall.
That's it.
Gunsmiths like Wilson Combat can replace a 2 3/4" ejector assembly and the gun is then fully capable of shooting 3" shells.
In fact, you can FIRE a 3" shell in a 2 3/4" receiver as long as you have a 3" chambered barrel, but due to the shorter ejector, the gun can't eject the longer shell.
Except for one or two special 870 models, you can use any barrel on any receiver within gauge.
However, if you want to use 3" shells you have to have a 3" chambered barrel and a receiver set up for 3" shells.
That's why the advisory. If you buy a 3" barrel you can't use it on an unaltered 2 3/4" receiver to shoot 3" shells.
You can shoot 2 3/4" shells."