Shellshucker:
Well, if you would have utilized a Number 1 or a Long Lee or even a C.L.L.M. or C.L.L.E. action for your build & did it up in .444 Marlin, or .40-70 Sharps Straight, or .405 W.C.F., or .375 2 1/2", or even .35 W.C.F., you'd be in the general ball-park, as a stopping rifle, but I'm not sure about .45ACP, although I suppose you might be able to rechamber it to something on the 9.3x74R case, shortened & blown out.
Mike Web

You are correct, sir!
Dogleg:
Beautiful Number 2 Pattern High Velocity Sporting Rifle. Was it made by B.S.A.Co. or by L.S.A.Co.Ld.?
Rugdoc:
It sounds very much like a factory "Lee Speed" type sporting rifle. The red wood was actually old Pre-War (Pre First World War, that is) French walnut, likely stained with red root (alkanet root) oil, as most of them were.
You know it amazes me, although it should not anymore, that some people who have nothing to add to the topic at hand, just add a non-relevant comment / photo, or both, presumably to up their post count, or because they have nothing better to do, or cannot find a post they are interested in, or simply know nothing of the subject matter at hand, but quickly reveal their ignorance of the subject by posting what they post!
OK, enough rant for today. Here's an Army & Navy Co-operative Society Limited Number 1 Pattern High Velocity Sporting Rifle, built by Birmingham Small Arms Company, while Mr. Jon Speed's Patent was still in effect. Note the B.S.A.Co. patent stalking safety.
I apologize for the poor quality of the photo.