I noticed that I have no actual pictures of the blow back chamber modification. oops.
Um, yeah, It took me a while to get around to finishing this but here it is;
As you can see I had to add some campfers to the blow back chamber. The little blueprint drawings show the "Modified" and "Unmodified" Chamber drawings. From there I think it's pretty self explanitory as to how you do the same thing on the opposite side of the coinciding marks on the inside of the slide. Indicated by the MGS styled exclamation point over the red circle.
Just grind them down with a rotory tool untill they fit flush and make them as even as possible for the best fit.
Since starting this project I've tried a couple of different parts swaps to get things down to a more smooth transition, but alas, this is the only way to get the parts to cooperate and work flawlessly.
This is basically a Defender with the Walther slide, trigger guard, and grips swapped over. Not that it matters performance wise. The only thing I've managed to accomplish was an outer barrel swap since completing this project orriginally. That was not easy. I used a reamer to open the barrel up for the inner barrel which was such a tight fit I had to hammer it in with a wood block and a rubber mallet. I swapped the hop up nub for a piece of styrene that was shaped to fit and I'll see if that actually helps hop up response when I get a few more Co2 cylinders later.
One thing to note about the difference in parts is that the Defenders slide was noticeably heavier and because of that they included a heavier recoil spring. It makes a big difference over the orriginal Walther spring which was anemic at best. You could hold the gun pointing up and the slide would stay back. The Defenders spring doesn't allow this. So you have a couple of options depending on how you like your blow back.
From the results of this project so far I suggest you use BB's heavier than .25's. The combination of the slide and blow back chamber causes some beneficial power boost results. The hop up, coincidentally, was never intended for velocities over 350 fps. it gets super sensitive and likes to send your bb's to the sky. Personally, I'm still experimenting, but getting better results after testing. If I find a permanent solution I will try to remember to share.
Some pictures of the new outer barrel and the slide lock I managed to persude to work from the 4.5mm frame. The gun now has all the features of the 4.5mm version.
Almost As sexy as the Maruzen with the mock silencer kit attached, lol.