Were the guns used in WW2 more advanced than those used in the American Civil War?

Far more advanced.

While cartridge weapons were in use, the metallic cartridge was still not perfected. The repeating firearm had been developed but that was hardly any match for a firearm that used a metallic cartridge with a more advanced gun power.

Advances in the "guns" as opposed to small arms were also numerous. Breech loaded cannons were not common in the civil war. By the time WWII rolled around breech loaded cannons (guns) were considered museum pieces. The "long tom" could fire and hit targets well out of line of sight. Most of the guns in the civil war used line of sight for targeting.

In the civil war, iron clad ships were first used in combat. By the time of WWII iron clad ships were the norm. They still had wooden boats (PT boats and mine sweeps). Steam power and the internal comusbustion engine had done away with sailing vessels being considered combat vessels.

I have strayed- a gun in the military is a large bore weapon used as artillery and yes the artillery of WWII was drastically different from even the most advanced unit of the civil war.

very much more advanced

You're comparing finnicky single shot rifles that get disabled if the black powder gets wet to bolt action rifles that have a decent rate of fire. And I'm not even talking about submachine guns, semi automatic rifles, machine guns that can be carried around by 1-2 people (unlike a gattling gun which has to be wheeled around), and artillery pieces with much greater range and more effective shells.

yes. The Germans also had the first modern assault rifles although I think Hitler limited their use as he believed the soldiers should have standard rifles. Fully automatic weapons were widely used in WW2 as well as machine guns.

During the American civil war most guns were muzzle loaders requiring the person to put powder and shot into the muzzle end of the gun and ram it down before firing. The North started to use rifling which is boring a twisted cut along the inside of the gun barrel that caused the bullet to spin greatly improving accuracy.. When the Confederates first encountered this weapon the old was to walk towards your enemy as the old muskets were so inaccurate then run the last 50 yards where the accuracy of fire was more dangerous. When rifling was introduced it tripled the distance the rifles could fire accurately and with the Confederates were mown down before they started their 50 yard charge.

Back then a 3 shot a minute rate of fire was acceptable but by WW2 they were able to fire hundreds of shots a minute with some guns.

A WW2 U.S. Infantry Battalion had 10x the amount of firepower than Civil War Union Corps.

yes

A 1000 times more advanced

Yes. Of course. In WW2, US soldiers used the M1 Garand. while the Springfield Model 1861 was the most widely used rifle of the civil war.

Nope military technology has obviously been on the decline since the civil war. The muzzle loader will always be the best and most efficient gun ever.