Loading for Walther PDP

[K31Scout]

I have a new full size 4.5" barrel PDP.  It has a stepped chamber and the spent brass has a bottle neck look to it due to the step.  It really keeps my brass cleaner due to the tight seal.  I've read the tight chamber gives about 50fps more velocity and I can attest to that.  Here's some recent data I got with 115gr Hornady XTP with Power Pistol.


6.1grs at 1.080 COL = 1255fps average.

Hornady manual says out of their 4" test barrel at 1.070" COL = 1150fps. My Walther is fast even considering the 1/2" more barrel with the PDP and a longer COL.


Max charge of Power Pistol with the 115gr XTP is 6.7grs according to the Hornady manual and lists 1250fps with that bullet and load.


So my question; is that stepped chamber increasing pressure and should I stop at 6.1gr of P.P. or is it like free speed like a longer barrel would give?  I'm not looking for a competition power factor, just curious as to what is driving those XTP's so fast. I  have not measured case heads yet but plan to on my next outing. 

[SI VIS PACEM PARRABELLUM]

The Walther barrel has polygonal rifling I believe so that could factor in with the higher velocity. I'd simply follow the basic handloading rules working up to and approaching max loads cautiously. I settled on 5.8 gr. of PP under a 115 gr. fmj. Sorry I don't have a chrono to give those results but that was/is a good recipe for my CZ's

[Wobbly]

You don't get something for nothing.

I don't know anything about the Walther or its barrel, but if it is generating a higher velocity, then that can only be due to higher chamber pressure. Since there is a relationship between pressure and velocity, and since chamber pressure defines the Max Load, I'd be paying great attention to the velocity listed there.

And too, since nothing good happens at Max Load, I'd be stopping shy of that velocity number.

Hope this helps.

[K31Scout]

My first thought was higher pressure too Wobbly, thanks for the confirmation.  Maybe I have a hot lot number of Power Pistol and I'm glad I didn't load any rounds higher than 6.1grs.  A good case for always using a chronograph for load development.