Thanks for the information, guys. The chambers on this one are 2 7/8". It has 31" barrels and weighs 7lbs. 11oz.
I was sent some more information saying J.L. took over the Toronto shop from his father, W.G., and started marking the guns with his name in 1877. This continued until 1886 when it went back to W.G. Rawbone, so that narrows the date.