A few comments:
BrassFetcher's tests on the links above for 000 buck and a WINCHESTER Foster 1 oz slug were into 20% (NOT FBI spec 10%) ballistic gel. The penetration in 20% gel is far less. Do your research to discover the difference. It is NOT a 2:1 ratio.
Labs do this (and smart "home testers") so that there standard size block has a better chance of stopping/catching the projectile, then using the well established math to correct the results for the "standard". Also, as in the case of buck and slug, you can literally blast to smithereens a 'standard' size block. There isn't a block afterwards, just widely scattered chunks. You go with a HUGH non standard size block or increase the density
On BRI sabots. Chase my posts. The 1966 Gun Digest had a large 5+ page article on them. They were tested in MANY types of shotguns: doubles side by & stacked with many chokes NOT JUST cylinder to improved cylinder. In Single shots, bolts, pumps and autos. Again in all chokes including full. This was well before "rifled barrels" were a manufacturer option. They were made with smoothbores in mind. There was a zinc projectile and a lead projectile. The zinc had the same dimensions but due to metal density was 260 grain instead of "an ounce". The zinc were much faster and marketed for police use. My hunting experience and antidotes are mostly from after Winchester's acquisition of the product. They didn't seem to have the 'slap down' of a full bore slug. Winchester added a hollow point cavity to them. Nobody I've talked to has recovered one that looked like it expanded (as opposed to just mangling the nose a bit) or on pass throughs thought it had acted like an expanding bullet. No gaping exits. Performance often disappointing to these guys, with comments comparing it to the same as a .50 cal muzzleloader ball. Save your indignant defense of blackpowder. We had all generally been slug hunters that switched to our .45 and .50 patched ball rifles for GUN season due to their accuracy increase and "good enough" on whitetail power as the regs changed. The users of BRI/Win slugs I'd encountered almost to a man had gone to it with .50 patched ball experience behind them, hoping for an improvement and seeing less authority than a fullbore 12 ga slug, less accuracy than their "mountain rifles". Blackpowder with saboted .44 and .45 pistol bullets were still on the horizon. They continue to sell in southern Michigan and northern Indiana but I see no product difference from the 1990 versions.