In spite of the reinforcing band, the 20-pounder earned a dubious reputation for bursting without warning, killing or injuring gunners.

Robert Parker Parrott was an ordnance officer in the US Army who inspected cannons manufactured at the West Point Foundry in Cold Spring, New York.

Several years before the American Civil War, gun founders grappled with the problem of rifling cannons.

Windage caused the propellant gases from the gunpowder explosion to leak out, but it also put less stress on the gun barrel.

With rifled cannon, the ammunition was designed to expand the shell so that there was no windage between the projectile and the gun barrel.

Ordnance Department trusted Robert Parrott to such a degree that he was allowed to be the inspecting officer until the end of 1862.

The rifling consisted of five lands and grooves of right-hand gaining twist (increasing toward the muzzle) and the caliber (bore diameter) was 3.67 in (93 mm).

[8] A number of the guns were designed for Navy use and had a block and pin that fitted over the cascabel (end knob).

The Confederate pattern differed from the Federal gun by having a reinforcing band 20 in (51 cm) long and 2 in (51 mm) thick.

The Noble Brothers & Company of Rome, Georgia contracted to manufacture 20-pounder Parrott rifles for the Confederacy, but it is not known if they were produced and none have survived.

[10] The 20-pounder Parrott rifle had a bore (caliber) with a diameter of 3.67 in (93 mm) and fired a projectile weighing 20 lb (9.1 kg).

The gunpowder charge weighed 2.0 lb (0.9 kg) and fired the projectile with a muzzle velocity of 1,250 ft/s (381 m/s) to a distance of 1,900 yd (1,737 m) at 5° elevation.

[11] A smoothbore cannon's projectile usually retained only one-third of its muzzle velocity at 1,500 yd (1,372 m) and its round shot could be seen in the air.

Tumbling occurred when the shell failed to take the grooves inside the gun barrel or when the spin wore off in flight.

This meant that the final impulse on the projectile as it left the gun was on its base, possibly causing the shell to wobble in flight.

[31] The Artillery Reserve was posted on the east bank of the Rappahannock River on Stafford Heights, opposite the town of Fredericksburg, Virginia.

[33] On the first day, Captain Henry Richardson's Battery D, 1st Missouri Light Artillery helped repel two Confederate attacks but lost one gun.

[35] However, the tide turned and Federal troops recaptured the position, re-manned the guns, and fired on the retreating Confederates.

[37] Union General Quincy Adams Gillmore believed that Parrott rifles were as good as the best artillery despite their "unequal endurance".

Confederate Major John Haskell wanted the 20-pounder Parrotts taken away from the Macon Light Artillery to spare its men possible injury.

Union General Hunt protested that the 20-pounder Parrotts were "very unsatisfactory"[38] because the shells were unreliable and dangerous to Federal troops.