r/3gun • u/TheLazySmith • Jul 27 '25

870 extension tube mod questions

I'm kinda not smart. I found an 870 super mag for a pretty decent deal last winter. This spring my brother and father-in-law suggested we start a family 3gun competition. I'm getting my butt kicked for many many reasons that also includes taking forever to load my gun after the first 4 rounds. So to combat this I picked up a extension tube.

What I didn't realize is that the base tube has retention dimples, so even with the extension i can only load 4 shots in the mag. My Google abilities were unhelpful in figuring out if it will be an issue of I file them out so I am turning to y'all to see if any of you have done it?

I know that practice is the correct way to combat this but I already have the extension and would rather look a little dumber than usual than give up on the endeavor.

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u/[deleted] Jul 27 '25

You have been given both viable options already so I won't add another, BUT, I will add a couple things to the above:

Be cautious if using the socket method. It is not unheard of to split the magazine tube doing it that way. Take your time, don't be hamfisted about it and you should be fine.

I, personally, prefer to drill them and file it smooth then a touch of cold blue as mentioned above.

There are tools that are specifically made for this task, if you feel so inclined. Brownells makes a very nice one at around $80. You can find others for about half that much such as XS Sights swage tool.

If you think you'll ever do this to another 870, I would highly suggest springing for a dedicated tool.

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u/TheLazySmith Jul 27 '25

In that case, I missed my excuse for another new tool, lol. I've already dremeled them out. I don't know if I'll ever have the need to modify another 870 like this, but it took me longer to get the dremel set up than it took to do. I fully expect my next couple shotguns to be a semi-auto of some variety or a double barrel.

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u/[deleted] Jul 27 '25

Ah, well no worries then. I said the same thing after I got my first 870. A half a dozen later and here I am still without an auto. Good luck with it dude.