The Remington 90-t is a 12 gauge, single shot, break open, trap shotgun
Value of any firearm is based on the current condition of that particular firearm.
Dimensionally similar, but they are not exactly the same. A firearm with a 5.56x45 chamber can accommodate the .223 Remington cartridge, but a firearm with a .223 Remington chamber cannot accommodate the 5.56x45 cartridge.
A shotgun is a firearm. A revolver is a firearm. A pistol is a firearm. A rifle is a firearm. If you want even more specific -- A Remington 1187 is a firearm (shotgun). A Smith and Wesson 686 is a firearm (revolver). A Sig Sauer P226 is a firearm (pistol). A Colt 6920 is a firearm (rifle).
.223 Remington can be cycled in a 5.56x45 rifle; 5.56x45 should not be cycled in a .223 Remington firearm.
I don't see dbl in Remington, if you mean the dbl in general when when referring to a Remington firearm that's double as in double barrel shotgun, derringer, etc.
Remington serial numbers are unique identifiers engraved on firearms produced by the Remington Arms Company. They are typically used to trace the history, ownership, and manufacturing details of a firearm. The format and location of the serial number can vary depending on the model and year of production. For specific inquiries about a particular Remington firearm, you can often refer to Remington's official resources or consult a firearms expert.
Remington never made a model 84 anything, unless that's a typewriter or firetruck or something other then a firearm.
Not without endangering yourself and anyone else in the area. Stay with ammunition designed for the firearm you are shooting.
Quality firearm
That is too vague to answer. It depends on exactly which variation it is and what kind of condition it is in.
That is a statement, not a question. WikiAnswers is for questions. Please ask a question.
Google Remington scoremaster model 511. Several websites have information on this .22 firearm.