I have a couple Ranger made Interarms marked PPK/S pistols and I had a Houlton ME marked S&W PPK/S.
The Ranger made pistols vary slightly as one is extremely reliable with 90 gr XTPs and 90 gr Sig V-Crowns, while the second stumbles a bit with the truncated cone shaped XTPs. Both are extremely reliable with round nose FMJs.
The S&W PPK/S just wasn't. I don't turn guns back into money often but that was an ex exception. In addition to having some odd fire control issues, even after the recall, the extended tang is sharp edges and uncomfortable to carry IWB.
To a great extent the extended tang was a un unnecessary solution to a shooter problem. The PP series was designed in 1929 for the PP and 1931 for the PPK, with the PPK/S being a hybrid of the PP grip frame and the PPK slide to meet GCA 1968 import requirements. The larger grip frame is a plus anyway as it's a bit longer allowing a better grip on the pistol and it offers one more round in the magazine.
None of them were designed with a modern "high" grip in mind and they just should not be shot that way. Shoot them with the "low" style grip intended and the slide bite issues go away for all but the largest and fleshiest of hands.
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The PPK and PPK/S with their 3.5" barrels offer enough length to give good ballistic performance in .380 ACP where shorter 2.75" .380 ACP pistols will not.
It's been a long standing position by many shooters to just shoot ball ammunition in a small caliber like the .380 ACP and .32 ACP. that reasoning has however always been a little flawed or over simplified, and it also reflects improvements in .380 ACP hollow point design and ammunition over the years.
Hollow points like the 90 gr XTP and 90 gr V-crown do quite well in ballistic gel when launched at 1000 - 1050 fps, and good loads will achieve that in a 3.5" barrel. If the XTPs are launched slower in the 950-975 fps range expansion becomes in consistent and the ones that do not expand just act like FMJs and give FMJ penetration.
The V- Crowns still expand but start edging down below 12" as the velocity falls off.
From that perspective, the XTP hollow points are never a bad choice as worst case you get FMJ performance, and in a pistol capable of 1000 fps, they do quite well with good expansion and 12-13" penetration.
Similarly, the V-crowns are a good choice at 975 fps or better and get marginal around 950 fps.
Hollow points like the Speer Gold Dot and Hornady FTX expand well at short barrel velocities but come up a bit short on penetration at 10-11". Bullets like the 85 gr Magtech Guardian expand well but consistently under penetrate at around 10".
In other words:
- if you don't know the velocity obtained in your .380 ACP and/or are using a hollow point known to over expand and under penetrate; or
- suitable hollow points are not reliable in your .380 ACP;
then using an FMJ is your best choice. But if it's your automatic default, you're operating about 30 years behind the times and would benefit from looking at some current data and test results.