Many of the BP buffalo guns went sub-sonic prior to the bullet impacting the buffalo. This did not prevent the bullet from exiting the fist buffalo to kill another behind or beside it. There are many such-letters of Sharps, Remintons or Ballards doing this, which have been re-printed in books written about 'those' times - wee, for instance Frank Sellers book on the Sharps Rifles.

Due to the relatively small case capacity of the .45/70, not enough TB can be loaded to get good supersonic loads, as-is the outcome of the larger cases.

A pure lead or lamsot pure lead bullet starting at 1,000fps will be a good killer of deer to well over 100yards or whatever range you can place one properly.

The original factory load for a .45/70 put a 500gr. almost pure lead bullet out the 32" bl. of the rifle at about 1,210fps. From a Carbine's 24" bl. it could have been about or at least 100fps slower. It was capable of exiting a bullalo at 200 to 400yards, according to the letters of buffalo hunters, long after it had gone subsonic - about 50 yards out.

At what range do you think 'Ol Elmer's 245gr. Keith bullets went subsonic after being launched at 1,200fps from a 4" .44SPL? - about the same or slightly closer. Maybe 50yards for his 22gr. 2400 from his engraved M29 in 4". Every one he put through a mule deer, exited - Elmer wasn't prone to shooting little 200pound spike bucks, btw. What range - witnessed at 600yards! So what if it was only 400? I've shot my own 4" with 275gr. SWC at 1,200fps at 400yards and I know dang well I can hit a deer at that range with it & I am certainly No Elmer Keith. I"m also quite sure they'd probably exit.

Now, put a 500gr. .458" bullet out at 1,000fps to 1,100fps to maintain subsonic flight and go shoot a deer - or buffalo, just keep 'em inside 300yards, just to be sure of an accurate shot. Express sights help.