I have a model 1873 Trapdoor Springfield that shoots 45/70 ammo. Have been wondering if the modern ammo is safe to use in it. I've never shot it and would like to try it out, just don't want to "damage" it or myself in the process.
If the gun is in good shape the "black powder equivalent" loads should be safe to fire in it. I wouldn't use the modern hunting rounds intended for the newer firearms. I also have a Trapdoor and it's fun to break it out when the guys come by to shoot their AR's and such. That thing kicks worse than my 458 SOCOM.
I'm in the Shreveport area so help is not far away. As has been said, use only black powder (or equivalent) loads. While there are some modern powders that have a low enough pressure, they have a higher flame temp. Another problem is the Trapdoors have a larger bore than we think of as 45 today, often .464 & sometimes bigger. Fear not, I have the correct bullet mold (405 grain).
If you pm me the serial number (X out the last couple of digits if you wish), I'll tell you when it was made. Don't be surprised if it's not a model 1873, they didn't change the markings right away.
Best to look for Cowboy Action loads. I've found Ultramax CB45701 at 940 ft/lbs and 1100 FPS to work, think I got it at Cabelas or might have been Bass Pro. I've googled others but haven't tried them. Powder River also looks like they have some good trapdoor products. Definitely no modern high pressure 45-70 ammo.