I have one of the Remington 870 tactical shotguns with the screw in tube with the exterior vent system. My question is can I substitute a Remington Rem Choke rifled tube for the tube that comes with the gun? Anybody have any experience?

Not sure what an "exterior vent system" is, but I think you mean a ported choke. If the choke is I/C, try slugs that are made for a smooth bore and see what you get.

As long a you are using the proper Remington choke for the shotgun, it shouldn't be a problem to use a rifled choke. Make sure the slugs are made to be shot out of a rifle barrel.

Or you could buy a fully rifled barrel, either with rifle sights or a cantilever and get more accuracy.

call remington customer service and ask.