Nope......., I'm with Skippy here. SMG'\s were my work bread and butter and persona; weapon and I never saw such a thing. The round bar thinggy looks like it could be held in a vice but as skippy says, it'd be better if it was flat. The magazine is a 1959 Fazakerley made magazine. To be honest, it wou;d have been better if the mag had been cut short by half.
But never seen one neither has James Edmiston - and he owned the company!. However, it reminds me of another tool that some half wit designed to take up play in the axis holes main butt frame......... A ring punch! You could use it, but only once. Far better was to simply bore the original ovalised holes out, slightly oversize and then insert a couple of bushes, soft or silver soldered in place. They'd last forever........
And another piece of stupidity for the big bold and beefy M1919 Brownings that only Biffo the Vear would dream up. Maybe next time the question of stupid crops up......