I suspect that's the way John does it.

Hodgdon says the non-compressed full or max. load is loaded to the seated bullet's base. The starting load is 70% of that amount. They also stated they could not get close to any modern rifle's max, pressure wise, loaded this way and that the highest speed they achieved was with a 180gr. jacketed bullet in a .300 magnum- at soemthing like 1,785fps IIRC.

That's roughly the same speed I got with 3,7gr. in my .17AH with 25g.r HP/s. Their report is like a .22LR with groups 1/2 my little fingernail at 50 yards, and the duplex reticle 9scoep set at 18X.

I've used it in a .375/06IMP, .45/60, .375 Winchester, .17AH, .22Hornet - started and stayed with the max load as felt a waste of time to download it.
The .375 bottlenecked case ran 1,360fps (or thereabouts); 1,745fps from the AH; straight .375 900+change w/200gr. jacketed; 1,250fps .22 Hornet; 1,050fps long seated .45/60; - all max capacity loads and all very slow and soft pressure wise - go-pow loads.No hangfires, and good accuracy, all round.

some printed data - max load only: The loads with cast bullets are indicated.

.375H&H 235gr. 26.3gr. - 1,144fps - no pressure given
.40/65Win 400gr. 12.0gr. - 915fps - 21,200CUP
.416 Rem Mag. 350gr. 29.0gr. 1,143fps - 29,900CUP.
.416 Rigby 350gr. 35.0gr. 1,354fps - no pressure given
.450 3 1/4" Sharps 500gr.cast 29.0gr. 1,105fps 24,300CUP
.458 WinMag 385gr. cast 19.0gr. 1,123fps - 16,100CUP
.458 WinMag 405gr. cast 21.0gr. 1,082fps - 17,100CUP
.458 WinMag 485gr. cast 19.0gr. 962fps - 22,700CUP

The Hodgdon Annual Mannual 2009 gives the introduction for Trail Boss, however at that time, it's mostly handgun related as that was it's primary reason for being, ie: safe - reduced velocity loads for cowboy action shooting.

The next year the Mannual gave jacketed and cast data for a variety of other rounds, saying it was virtualy good for any bottlnecked or straight case if loaded without compression & that most if not all were OK with jacketed or cast bullets.

Due to the low velocity, but normal low (15,000 to 35,000PSI pressures, it turned out good for firelapping chores as well. It does not require a 'small volume charge which can give ignition or burning problems, and is virtually the easiest of all powders to use. On top of that, if used as directed, it CANNOT stick a bullet in the bore like can happen when jacketed bullets are driven too slowly with other powders using reduced loads.

The Hodgdon Annual Mannual 2010 has the article, loads, etc for the intermediate rounds with pressure listings - I gave my copy of the 2010 Hodgdon book away, unfortunately - I can't find it and did give one away.

edited for clarity, I hope.