On high power rifles like the 1886....curved butts deliver more of a kick than the flat shotgun style. . Did you slug the bore? Perhaps your 38 WCF was really a 44WCF. (Sometimes people interchange the brass lifter which sometimes has the caliber embossed in it.)
It was stamped .38 WCF and not re bored to a larger caliber. I had a 44-40 and the fired cases look completely different. As I had both at that time, I tried to fit a .44 into the .38 and it would not go.
Like I said, I read years later that the .38 was purposely chambered deeper and I figured out it was to split the case at the shoulder.