Just change the barrel?
Not to raise your anxiety too much, but no. Barry @ Bits may not want to tell you everything he's going to do, but in order for your PPK to function, he will
1. Change the barrel. This is the easiest part, if he knows what he's doing, 10 minutes
2. Open the breech face (long milling cutter) to the larger diameter needed for .380
3. (or maybe 2) Open the barrel port in the slide, since the barrel is a bigger diameter in .380
4. regrind the ejector so that the larger .380 round can get past it, but the slide still locks back on empty
If he doesn't do step 4, you will have
-Failure to feed
-Failure to extract (occasional)
-Magazine drops unexpectedly
and probably a few other problems I've forgotten.
I have done a few of these, and my painful discovery was that if I was going to do it again, I would need to use a broaching cutter to cut the slot in the frame needed for the new (Post-war) PPK .380 magazines, which have a tab on the magainze follower that needs a rib in the mag. That tab then trips the much flatter ejector, when it's time to lock back the slide on empty. The ejector is completely different in the modern .380, to avoid the 3 biggies (and probably other problems) -- failure to lock back on empty is your clue that the conversion is a bit of a botch.
Barry has done a lot more of these than most people here, but Walther redesigned the PPK in .380 for a reason. For reliable function, there is no choice but to do it right. Pre-War, the PPK and PP pistols in .380 were bottom magazine release, and the ejector (and frame) were different from the .32 versions as well.
Recoil spring the same? He knows you aren't going to shoot it much. .32 is reasonable recoil in a blowback pistol, .380 Walther recoil is the subject of a scientific study on another board devoted to Walther pistols. Suffice to say, Walther PPK .380 recoil is about the worst of any pistol, both measured and felt, and the recoil spring needs to be heavier or you'll be both sore and holding a damaged pistol in pretty short order.
One reason he may not want to change the spring (other than cost) is that the heavier recoil spring also demands a sturdier mechanism for locking back the slide. If Barry has found the "magic shape" which eluded me, allowing both the bigger .380 to get by and not trip the magazine release or fail to lock open on empty, there is not a lot of material left to hold the slide. A lighter recoil spring means less stress for that part -- maybe. Personally, I think the .30 Epps is the best "simple conversion". It's a shame there is no one reloading that cartridge commercially, or that would be all there would be. A pleasant round to shoot, a true "only the barrel changes" conversion, done well at half the cost.
If you want a .380 PPK, you should really start out with one, where only the barrel is changed. But hey, I'm a stupid hobbyist who doesn't do this for profit, so what do I know?
