You can't value anything with just a serial number. Who made it? What condition is it in? Is it a hand gun or a long gun?
Can't be answered without knowing who made it, all markings, box, papers, accessories, caliber/gauge, long gun or hand gun, finish, condition, etc..
It depends on what kind of shooting you do. Bulls-eye shooters hold the gun with one hand. Shooters that participate in practical shooting sports typically hold the gun with two. http://www.handgunsmag.com/tactics_training/HGcombatg_100206C.jpg
Any shape can be the biggest - as long as it is the biggest.
There is no such thing as the "biggest longer".
The .950 JDJ is the biggest rifle The biggest hand held gun is the 600 Nitro Express Pistol
.500s&w
You will have to define if you are talking about hand held or crew served.
The Potato Gun
The BATFE web site has information that can assist you in answering your question.
The biggest gun is a SPG gun the Monster which is a german rail gun mounts a 800mm mortar
a hand gun
The Paris gun made by the Germans in WWI.
Gun store.
who invented the six shooter hand gun
Oklahoma has the biggest, followed by Dallas, IIRC
break down a lorcin hand gun