express tube extension?

[twoshots]

I have an express 870 magnum. I would like to purchase a tube extension. the magtube has pinched cams to hold the plastic cap lock in place. Is there a standard procedure to allow the shell rim to pass through? I was going to turn up a round punch to press out the dents the required amount. I like to ask before I do something wrong thanks for any advice.

p.s. I searched threads, but found about 1.3 million that include express 870

also posted in gunsmithing

 

[Ike]

Most people either drill them out or punch them out somehow, but they have to come out before you can use a mag tube extension. Make sure the inside is smooth and doesn't catch the round.
The other thing to be aware of is that you will need a ball detent in your barrel or a tac 3-point sling attachment with the detent built in, otherwise your mag extension (with the exception of Dlask) will come loose. The detent keeps thee extension from unscrewing. Most Expresses don't come with the detent since they don't use the detent to hold the mag cap on.

Cheers