Your best bet is to purchase the butt stock for the .454 R92 which comes with an effective pad.
A factory replacement part for the Rossi R92 chambered in .454 Casull, this wooden stock assembly makes your lever gun look like new again.
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The Rossi Puma R92 is a near clone of a Winchester 1892. The steel crescent butt plate is an authentic touch as the Winchester 1892 to my limited knowledge never had a rubber pad, it had either a curved steel plate or in some cases a straight steel plate.
There are no commercial pads that fit, I have been through this with my R92 .44 Magnum. A gentleman on the MOF gave me his original stock and a buitt pad from the Rossi store on the Rossi website that he had purchased. He had cut his stock to remove the curved butt surface but the pad just did not fit the profile. He also gave me his orignal forward stock.
I plan to, already began the work, to add a small spacer section of stock (a piece from an old derelict stock I had laying around of no value). I will peg that piece and then use epoxy with micro-balloons to glue it on. Then I will reshape the entire piece to mate up with the gifted Rossi .454 butt pad. I will paint both the butt stock and fore stock black to match and to hide the wood work as there is no way to make the grain match. And of course set my original parts aside. It will be into the summer before I complete my "black" stock set with pad due to travel commitments and family business. But I am making headway
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My rifle left bruises on my arm after a short range session using standard Winchester White Box ammo. And I am not recoil adverse, the .44 Magnum has some punch. Until I get my new stock finished I am using home loads with the Hornady 240 XTP bullet and 10.0 grains of Unique powder producing 1200 FPS. Tolerable.
Problem with being authentic, as the CAS prefer and who purchase many R92 rifles, is that back in the olden times the .44-40 and .38-40 where quite anemic rounds compared to a .44 Magnum or todays hot loaded .45 Colt. It looks good, but it is painful with full power loads.