im considering adding a 5 round extension tube to my 870.  

im concerned that some of the shot may strike the tube & go unwanted places.

is my concern well founded?

btw, dont let the california address make you prejudiced.  i lived in north central ohio & east tennessee for 28 years before moving to this accursed state.  i would ask someone back home, but the time difference makes that kind of hard.

thanks.

How long's your barrel?

18.5 inches.

i have an offer to trade for a 20 even up if i need to.

By 5 round extension, do you mean an extension that ADDS 5 rounds to the 4 round magazine tube?
That would mean 10 shots total with the chamber loaded, and that tube would stick out awfully far.

A standard 18" barrel is usually fitted with a +2 extension which means a total of 7 rounds with the chamber loaded.  That would not stick out beyond the muzzle.

If you get a 20" barrel you can use a +3, or total of 8 rounds with the chamber loaded without sticking beyond the barrel.

The long 10 shot extensions are only for 26" barrels.  Putting one of these on a 18" or 20" barrel and there is a chance of the shot damaging the extension.

Plus, there's not enough support for that long an extension on a shorter barrel.  A not-to-hard bump will either bend something or knock the extension off.

In either case, the gun's original magazine tube is usually the part that gets damaged.  This means a trip back to Remington to have a new magazine tube installed.

Best advice: If you have a 18" barrel buy a +2 or 7 shot total extension.
If you get the 20", buy a +3 or 8 shot total extension.

Whatever you get, BUY AND USE A BARREL CLAMP.  The clamp prevents bending or knocking the extension off.  How strong the extension is doesn't matter.  The GUN'S magazine tube is the weak link.

why thank you muchly.