Ok its been guessed, now who fancies firing some? Its obviously not handloads so it may even shoot decent groups, its a 55 grain bullet in a sabot collet inside a .308 Remington case. way of having 22-2540 performance without a second rifle although I imagine you would need to alter the sights a fair bit
I would be very interested to hear how you get on with these rounds.
Theoretically the sabot round has a much lower moment of inertia than the full bore round so it may need much tighter rifling to get the same stability.
Firing such rounds from barrels intended for full bore projectiles may explain the accuracy problems many users report.
Though I suspect factory rounds may be far better than the hand loads many people have problems with.
I have a target barrelled P14 action that may be used for this. Its a 1960's rebarrel so its not a S&L or Bl;ack Mountain. I think its no faster than 1 in 10 which has stabilised 220 grain .308 match kings out to 1000 yards but may not really be up to it!
They can sit in the cupboard gathering dust like the 1960s Kynoch Long Range Streamline match ammo I have for .303.
They werent made in 38-200 as expected. They were offered again in 1939 in .455 Webley but we wanted the anaemic 38-200 round so it was dropped.
Production in .455 Webley ran to 1917 when the US Govt forced production to be only 45 ACP with half moon clips. This model (I know its a crap photo!) was an actual Govt purchase and is marked as such. I sometimes miss my old one!