Maruzen P38 Slide Stuck

[TB3]

Hi all,
I've got a reasonable new (1 month or so) Maruzen P38 'Detachable' (the UNCLE gun.) I've put a few rounds through it with propane using the Gun Gas adaptor kit. Now, the Detachable has a threaded barrel to take various accessories. It comes with a tiny flash suppressor, an I just got a barrel extension and 'silencer'.

When I removed the flash suppressor and threaded on the barrel extension the problems started. The slide wouldn't pull back, so I took it off and tried just the silencer. That worked okay, so I tried the extension again. Still no joy. the extension doesn't block the slide, but something did seem to be pushing the barrel back a tiny bit, just enough to block the magazine from being pushed into the locked position. I took it apart (I've stripped P38s before and the GBB works exactly the same way), but after I put it back together and slid the slide forward it got stuck in the forward position.

The first step to stripping the gun is to pull the slide back, and since I can't do that, I'm at a loss. I've checked everything I can think of, and right now the gun is sitting beside me, no attachments, no magazine, and stuck.

Does anybody have any idea what I can do? Does anyone have a WWII-type P38 who's had some experience with them? The Detachable is exactly the same GBB, with different furniture.

Thanks.