Having completed a few more tests (albeit not range tests as the temperatures hereabouts have lately been well into the -30’s with wind-chill - [90 more days til spring]) using an assortment of old British rounds I have kicking around, I now believe the rifle to be chambered in .360 N.E. 2 1/4" with .356" lands and .374" grooves.

Looking through Hoyen's & Fleming's books confirms that .360's came in a wide variety of bore sizes.

In any event, a magazine full of assorted Eley & Kynoch .360 rounds feed MUCH better from the magazine than did the 38-55 rounds.

I haven't been paying full attention to this rifle as I recently picked up a neglected old W. W. Greener take-down Club Rifle in .310 Greener and 2 spare barrels with fore-arms, one in .22 Long Rifle, which will soon be re-chambered to .218 Bee & a spare in .310, chambered with a 32-20 reamer.

93x64mm
I already have a 375 2 1/2" still in the stable, although it is a Trade Pattern Farquharson and not a Lee Speed.

I'll have to figure out how to post photos now that Photobucket is pay only, which I refuse to participate in.