I am sure this will cause some squawking, but IMHO the mounting system is considerably more important than the brand of scope in determining durability. Virtually all of the top quality scopes (Burris, Leupold, Bushnell, Nikon) will withstand the recoil of a 45/70, if properly mounted. Although my preference is Burris.
Scope failure is caused by scope flex. Believe it, or not, the upward inertia of handgun recoil causes the scope tube to flex which stresses the objective housing and internal components. The remedy is a rigid mounting system. This means no less than three (preferably more) rings, and 6 mounting screws.
I have four rings on my gun, and have had the base and receiver modified to a 6 screw mounting system using oversize 8-40 screws. The current scope is a Burris 2X, but I have used a 2 x 6 Bushnell and a Burris 2 x 7 on 45/70 handguns with no problem. I have a .454 Casull Raging Bull with a 1.5 x 4 Burris variable and five rings (its a long scope), which has taken over 2000 full house 335 gr Casull rounds without failure.
I did not get this out of a book, but learned the hard way through destroying at least one of every major manufacturers' scopes in the process. Some scope brands have gotten undeserved bad reputations because of improper mounting. Since eliminating base and scope flex, I have had only one scope failure. That was a twenty something year old Leupold where the old seals just gave out due to climate extremes. That is not a problem with more recent scopes.
In addition, very few out of the box scope rings are perfectly round inside. This means rings will not fully contact and/or grip the scope tube, and slippage will result. (Burris Signature rings are the exception because of the nylon inserts.) If you have a scope with the telltale lines where the ring halves join, you have slippage. Ruger SRH factory rings are chief offenders in the slippage category. This can be easily remedied.
The rings need to be reamed to ensure full contact with the scope, and the sharp edges on the inside of the ring halves need to be broken with a fine file. You can have your gunsmith do the job, or you can order a Clymer scope ring reamer from Brownells. Dymo label tape makes a fine friction material, and can be stacked inside the ring(s) to compensate when more elevation is needed. It is sticky on one side, and will stay in place.
Sorry to have rambled on, but if you have a sufficient number of rings that fit your scope and you eliminate base flex, you will have gone a long way toward permanently eliminating scope failures. Good luck.
