Great idea. how does the capacity compare to other hives? On a different post there was some concern that a regular(?) 48 in. TBH was undersize for the job and maybe should be stretched to 5 ft. How about splicing the barrels, to increase the length to 48 in.or more? Robo posts show a comb about 22inches by 11 inches ( just a guess!). How big is too big?

I am just starting out (next spring) and planing to build at least two TBHs and I am trying to minimize my mistakes.

Thanks in advance

That is a pretty good guess. A standard 55 gallon barrel/drum will be about 24" in diameter and 34.5" long (tall). Using
this nifty calculator we can see that 1/2 of this cylinder holds a volume of roughly 7804 cu/in.
Using a
similar calculator we can take the dimensions of a trapazoid TBH (the plans from the book we apparent aren't allowed to mention here). 11" H, 5" Bottom, 15.25" top (I'm estimating here, the plans aren't 100% clear).
48" (4ft) long would have a volume of roughly 5346 cu/in
60" (5ft) long would have a volume of roughly 6682.5 cu/in
So a drum TBH would have the volume of a 70" (5ft 10") TBH using the dimensions above.
Just for fun, a 48" (4ft) long drum would have a volume around 10,857 cu/in
A 60" (5ft) would have a volume around 13,572 cu/in