He seemed to get carried away on calling the 44mag a 42 cal. Trying to impress us I guess. We call the 30cals that because somewhere down the line they decided to name calibers after the hole drilled, before they rifled the barrel, figure rifling for jacketed bullets about .004 deep and you get 308 diameter bullets. BUT, pistol calibers like the 44 started to get named after case diameter. Best example is the 38 special. When cartridges started taking over they were converting cap and ball revolvers to cartridge guns. A Colt Navy or 36 Army had a cylinder that took a 380 ball. To convert they had cartridges similar to our 22 LR in which you had a heel to fit in the case and the bullet diameter the same as the case. Worked very well for these conversions Even when they started to make different cartridges like the various 38's we see where you have a more traditional cartridge, the 38 cal moniker stuck. The "44" revolvers were actually 45's taking a 454 ball. The case dimension of the 44 mag is about 456. But the revolvers were called 44's so the name 44 for a variety of cartridges stuck when they started loading them normally. Europeans use the diameter of the bullet for their designations with the exception of the English which use our system. My 303 brit is supposed to have a 311 bullet. .004 rifling added on to a 303 diameter hole gives you the 311.
As an old English playwright said "A big ado about nothing"
They sell both locally and the Cinder blocks are lighter weight. I had a old Brown Bess musket that I played with. It took a 715 round ball that weighed over 500 grains. When I went to match one time, they provided a few gongs for people to plink at. I loaded the old Bess with 90 to 100 grains of powder which may have given 900 fps. People would walk up to the gongs with various heavy loads in their smaller caliber rifles and get a kick out of how they would swing. I shot one of those gongs and wrapped the chain twice where another pulled out of the ground. That big heavy slow round ball would not shatter like the faster rifles were doing. When you looked at the base of the gongs you would find only fragments except for the ball from the Bess which were large discs (some fragmenting) . More energy was retained due to the sheer mass of the ball and the slower velocity. The rifles probably did as much damage to live tissue as the old Bess but on solid objects it was better. The cement block test showed that the lighter 30-30 bullets shattered more on cement and nothing more.
DEP