Andy,
When I bought the converted rifle in the video I wasn't sure just how the x45 to x39 conversion had been carried out. Initially I thought it might have been converted with a chamber insert, like yours.
Once I got it home and compared it to the 52 and 52/57 it was obvious that the barrel of the converted rifle was shortened by 1 cm from the breach end and re chambered. Likewise the "connecting rod/slide" in the gas system was shortened by 1 cm. I have no idea who did the conversion.
The converted rifle runs 100% if I use the Vz- 52/57 mag, but with the original Vz-52 7.62x45mm mag there is the occasional FTF.
I have a limited amount of surplus 7.62x45 ammo, I shot some of it years ago but I think I'll just keep the rest. I should have bought more - it was something like $2.50 a box back when I got the rifle!
Yep, no hiding the fact that the video is "shot" in PEI. My "custom" gun rest is made from a feed bag sewn into three compartments filled with dried beans - much nicer than a sand bag & easier to lug around too.