There are numberous ones. The only limitation is your bank account.
50's or so
Yes, I can. A Barrett M107 is a .50 caliber sniper rifle.
In the case of the Barrett M82 rifle, about 30-31 lbs, depending on the model. The scope may add several more pounds if a night vision scope is used.
It will require that the rifle be drilled and tapped for scope mounts. Some small rifles (usually .22 rimfire) can use a dovetail mount, but those rifles are made with the dovetail grooves, and they will not work with a heavy recoiling caliber. There are a very few scope mounts that use existing rear sight bases to mount the scope, but it will be very far forward on a T/C, and need a long eye relief scope. Your best course would be to have a smith do a professional D&T for your rifle- relatively cheap to do.
You need to give us some more information to answer your question- there are dozens of firearms that would fall under "50 rifle". If you mean a Barrett .50 caliber rifle, anywhere from $6,500 to $10,000- plus another $2000 for a scope.
50 caliber
Yes
50-150
Any bullet that has a diameter of one half inch is a .50 caliber bullet. There are different .50 caliber bullets- my Hawken muzzle loading rifle shoots a .50 caliber lead bullet, but different from the .50 Browning Machine Gun (that is also used in the .50 Barret sniper rifle)
how far does a 50 caliber sniper rifle shoot accuratly
Over a mile.
50-75