I currently own four .45-70 rifles, an 1873 Trapdoor Springfield, a Marlin 1895, a Siamese Mauser conversion, and a Wickliffe 76 single shot falling block. I use nothing except my own handloads, tailored for the strength of the different actions. For many years, ammo companies held .45-70 factory loads to around 18-20k psi pressures in deference to the weaker design of the many old Trapdoor rifles that were still in use. SAAMI Standard factory load max pressure for the .45-70 is 28,000 CUP, but that pressure is said to be too high for original Trapdoor rifles. Buffalo Bore Standard Pressure loads are loaded to this higher SAAMI pressure, so not good in the Trapdoor. Here is a company that loads .45-70 400 gr. loads that they say are loaded to 20k psi, for the Trapdoors. Note that some of the loads they sell are not "Trapdoor Safe"
https://steinelammo.com/product-category/rifle-ammo/45-70-govt/Here's another I had not heard of:
https://precisiononeammunition.com/product/45-70-350-grain-fp-trapdoor/I think that is still the case with SOME factory ammo. The Remington 405 gr. loads at 1320 fps are said to be safe for Trapdoors, and the Winchester Super-X Cowboy Action Ammo 45-70 Government 405 Grain Lead loads as well. But there are hotter higher pressure factory loads available like the relatively recent Hornady LeverEvolution, which are intended only for the stronger modern lever guns and Ruger #1, Siamese Mauser, etc., so you need to be aware of that.
If you handload, you will see the loading manuals publish three different sets of data for the .45-70. There are loads that are held under about 20k psi for the Trapdoor rifles. The next tier of loads are intended for the modern lever action rifles such as the Winchester 1886 or the Marlin 1895. As I recall, but don't quote me, these loads are held to around 36k psi or less. Then the hottest .45-70 loads are intended for the strongest actions such as the Ruger #1 and #3, the Wickliffe 76, and Siamese Mauser bolt action conversions. I think these hotter handloads top out around 45-48k psi, but again am going from memory because I am away from my books. The .45-70 becomes a much different animal when you run it with the hot handloads.
I was recently reading a very old Thread from the late Michael Petrov. He said he had done a blow-up test on a Trapdoor Springfield rifle, and was surprised at what it took before failing. However, he said he would never publish the results of his tests. And despite stronger modern steel used in the modern H&R Trapdoor, I would not dream of using the hotter modern factory loads or hot handloads that are intended for stronger action designs. I have also never heard what loads are safe in the modern Brass frame Henry lever action .45-70 rifles.
I have a friend who loves his .45-70 rifles, and he told me he fired a mid-level .45-70 load in one of the H&R break open action single shots. He is a pretty big boy at about 6' 4" and 260lbs, but said the recoil from that little single shot really got his attention. The gun didn't blow up, and he didn't fire any more either.
And always remember... In God we trust... but always verify any ammunition load recommendations you get from ANYONE on the internet.
