Just found this: http://uk.youtube.com/watch?v=ihk3BHXu4 ... re=related
It looks like a fairly non-intrusive blowback mod for the Tommy and (a) lot's of people seem to have got it to work and (b) I think it would also work for the 1928 receivers that some of us have on order....
I made a kit up a while back that was more reliable and less potentially damaging to the gearbox than just a piece of coat-hanger. I didn't market it/post it on here because I thought the end result was rather tacky looking and sounding. Basically the kit included a thin metal rod, threaded on one end to accept the piston head thread, and a matching smooth-bored spring guide for the rod to reciprocate through.
A Proud Member Of 'Team Spleen!' who play mainly at Gunman Airsoft, Tuddenham, Suffolk.
Having watched the vid again, I think that a few simple addition could improve this. I'm going to try it when ROSV get the Tommy back in stock (Old Faithfull is down for a 1928 conversion already):
(1) B&Q have some thin but stroing looking steel rod (for curtains I think) rather than a chopped up hanger
(2) I've got some tubing that I think will fit insde the spring guide and stop the rod moving about
(3) Padding the end of the rod should reduce impact on the plate - double coat of shrink wrap, trimmed down might do it
Failing that, I would have said wait for someone to do a commercial blowback m1a1 but given that the ACM toy makers seem to have all gone bust...