Got to looking up some data I took from an original receiver '86 with a heavy (about 1" wall barrel) and M71 breechblock and locking lugs, back in 2000. Pressure-time data was obtained with an Oehler 43PBL rig with the strain gage mounted over the chamber.
43.0 gr ReloadeR #7 and a Remington JFSP 405 gr. bullet Barrel length 20". Average MV = 1667 with Max p = 31,200 psi, Av p = 29,700 psi. Not recommended for people with shoulder problems even with a recoil pad!
Remington factory .45-70-405gr JFSP loads. Powder chg.: 28.0 gr MV (20" bbl) = 1343 ft/sec Av. p = 18,000 psi Max p = 20,300 psi
395 gr #457124 cast from Lyman #2 equivalent: Powder: IMR4198 + 1/4 square single-ply toilet paper pressed lightly into case and allowed to compress by seating bullet. Av. MV = 1261 ft/sec Av. Max p = 14,900 psi, Max p = 15,700 psi
Similar load on a different day, Av. MV = 1322 ft/sec Av. Max p = 19.600 psi Max p = 20,800 psi Used TP filler for years with NO signs of barrel ringing.
33 WCF M1886/M71 breechblock & locking lugs. 24" barrel. Bullet: Hornady 200 gr. JRNFP Powder: Herters #100, mfg by Eley-Kynoch in the 1960's. Later briefly marketed as Scot Powder Co. #4351. Burning rate somewhere between IMR4320 and IMR4350, but with small grains. Powder used old methyl-centralite coating. Av MV =2355 ft/sec Av. Max p = 39,100 psi Max p = 41,500 psi
Never had a chance to take game with this bullet. Old CCC bullets did a job on European wild boar, however.
NOTE: The measurements taken with the Oehler 43PBL are not to be taken as absolutely correct, as no factory calibration loads were available for either rifle or cartridge. But the Remington .45-70 factory loads could be taken as a good indication of the accuracy of measurements. Pressure-time curves were smooth in all instances.
Stay well and safe, Pards