Regular old time 'contact cement' will do nicely to affix leather to many surfaces, inclusive of the side or butt end of a rubber recoil pad. Will it last forever? No, or I should say probably not, but it is easily reaffixed should it ever become necessary. And it is removable, when wished.
TW,
Barge cement is the glue of choice for leather work as it remains flexible when fully cured, on the other hand contact cement will dry hard and won’t allow the leather to flex with the base material, which might result in separation… with time the leather will stiffen up creating creases or cracks
All Best,
CJ
