I’ve heard about this Remington 870 modification several times. I was not sure about it because it requires modification of the ejection window and it cannot be undone. This is the most radical way to improve reliability of your Remington 870, so if you don’t have many issues with extraction you don’t need it.
WARNING! This modification cannot be undone. Make it only if you are 100% sure.
But as author of the Rem870.com blog I need to check everything about Remington 870 and see if it works.
This upgrade will not harm your shotgun. It functions properly, but only tests and several hundreds of rounds can tell if this upgrade is good.
Here you can see two Remington 870 receivers, one is standard, secone one is modified:
Start process with fixing Remington 870 receiver in vise:
Then, carefully measure how much metal you need to remove with Dremel to make front part of the ejection port rectangular: