If you are not able to find out the information from your grandfather or photos or letters, then it depends:
The type of rifle or weapon? The type weapon used depended on which service, Army or Marine, which time period, which locations, which units and which job responsibilities. If you know most of that information, then it is possible to guess which type. The most commonly used rifle by the US Military in WW2 was the M1 Garand.
The actual specific weapon by serial number? It is not likely that any military record still exists, because these are local temporary records kept by the Company Supply Sergeant or the Company Armorer. The weapons can be changed out because of damage, loss, repairs or new assignments within the squad, platoon or company for example. The weapons belong to the company, and if a soldier transfers from one company to another, then the specific weapon will be turned in at the old unit, and he will be issued a new weapon at the new unit.
Various marks of the Lee-Enfield rifle in .303 calibre. Some were issued with Owen Guns (Australian made and designed 9mm submachine gun) and Tommy Guns.
US:M16 Vietcong:Ak-47
The Ross .303 rifle was initially issued to Canadian troops during World War 1. It was highly accurate, but due to its unreliability it was unsuitable for use in the muck and grime of the trenches and so was retained only by snipers and marksman. The rest of Canadian forces were reissued with the Lee-Enfield .303 SMLE.
50-500 depending on EXACTLY what you have , condition, accessories, etc..
The Hall Model 1819 rifle was issued in large numbers to the U.S. Army. Starting in 1821 and continuing for several years the rifle was distributed to various units. It was never considered the standard arm as it was considered to be too complicated for the average soldier to use.
why dont u ask ur grandfather!
M16A2 rifle
Kinda depends on what exactly it is. Several different types of rifle saw service in WWI.
Various marks of the Lee-Enfield rifle in .303 calibre. Some were issued with Owen Guns (Australian made and designed 9mm submachine gun) and Tommy Guns.
No
This was issued in 1967.
100-5000 depending on EXACTLY what you have
A few hundered to the GNP of a third world nation, depending on EXACTLY what you have.
The Karabiner 98K was the standard issued rifle of Nazi Germany.
The US M16 (AR15) was considered a "jungle rifle" by the US Army in the 1960s. The "Jungle Rifle" was only issued to US troops in jungle terrain (Central America, South Vietnam, South America, etc.). The official US Rifle during this period was the M14 rifle which was issued to all other US Soldiers & Marines everywhere else in the world including the US.
Depends on exactly which rifle(s) you refer to.
Depends on exactly what the rifle is, and how far it's disassembled.