[Slamfire]

Most 380's are blowback but Wiki says the Walther PK380 is a locked breech pistol.

Blowbacks are severly limited to what bullets and powders they can use, but locked breech pistols can use a wider range without function issues. Revolvers have the widest perating envelope, as long as you can pull the trigger they will go bang.

Try the heaviest bullets that will feed and extract without blowing case heads or primers.