The Martini Gallery is a nice place to start. Some very good information to found there. There are a couple of Martini specific discussion boards around. Query Martini-Henry on www.google.com to find them.
I have a few BSAs, two left handed MkIIIs and a 12/15. They all shoot very well and I've not had any troubles with them. Very well built, but the MkIII is a tad on the heavy side. Makes a great prone gun.
The BSA Martini Inter. MkIII came in right and left handed. Lefthand is hard to fine. Loading is from the left side of the action. Barrel is free floating on the MkIII. Can email you pics if you're interested.
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