Planning to pick up a Remington 870 Express 18" with the 2 shot extension at the upcoming gun show this weekend. The only question I have is: With the extension, will there be a conflict adding another barrel to it? I want a longer barrel for skeet, but this will be primary a HD shottie with informal skeet shooting.

Also, I know about the dimples, but will it affect putting on a regular magazine cap to limit me to 5 shells so I can plug the barrel in case if I ever get into waterfowl hunting?

The Express Synthetic with the Remington factory extension HAS no dimples.

It's set up just like the Police and Wingmaster.
It has the spring loaded plunger on the front face of the barrel support that locks the extension OR the old style magazine cap in place.

All you'll need to convert to a 4 shot standard magazine is:
An OLD STYLE magazine cap.  An Express cap WON'T DO.
An old style magazine spring retainer.  This is a steel, split "Cup-washer" that inserts into the tube.
A standard magazine spring.
A Wingmaster barrel with the installed spring and plunger on the front face of the barrel support ring.

NOTE: that you'll have to be careful to buy a Wingmaster longer barrel WITH the spring and plunger installed.
The Express barrels have no plunger.

I thought all the newer express' came without the dimples..only the older models had them.
I coulda swore the 5 shot I saw at the shop the otehr day didnt have them...or am I confused?

you cant see them unless you remove the barrel. i bought my 870 maybie about 10 mouths ago now and it has the dimples..

the other thing you could do is just go and pick up a dowl and cut it to length for a plug if you plan on doing hunting with it..

Jess