Shortening a rifle barrel will reduce velocity (in most cases) but when done correctly does not reduce accuracy. The cut must be square with the bore, and the crown (end of the barrel) will need to be machined after the cut. The cut should normally be made on a lathe, and not with a hacksaw. BTW, 30 inches is a VERY long barrel for anything but a muzzle loading rifle!
Typically the crown of a gun is on the muzzle end of a rifle. It is the recessed area at the very end of the barrel. Poor crown cutting can be the cause of many accuracy problems.
For range and accuracy, a rifle
Increased accuracy and power.
Depends on which specific rifle you had in mind. They're usually determine by Minute of Arc (MOA).
bed the rear stock
If you do you will destroy a perfectly good rifle. The Whisper is designed to shoot Pellets not BB's. It has a rifled barrel (Grooves in the barrel to catch and spin the pellet) this makes them fly straighter. Pellets are a soft material. BB are a hard material. Forcing them through a rifles barrel will destroy the rifling. This is why BB rifles have smooth bore barrels. If you have started to shoot BB then you have already started to destroy the accuracy of the rifle and dropped it's value. So don't do it.
Depending upon many conditions -weather, type of projectile, condition of rifle bore, type of rifle, etc. - combat accuracy can be achieved out to around 600 yards/580 meters. Target accuracy with a highly accurate rifle can be stretched out to 1000 yards/ 990 meters.
good to very good. I have one.
Yes this gun has great accuracy if you adjust it and set hop up right
How long is a string? I have some rifles that are 26 inches long, and some that are 72 inches. Depends on which rifle.
About equal at ranges up to 300 m. Beyond that a slight advantage to M1A
14.5 inches on the actual M4 rifle.