Artillery Barrel Specs???

[sheepherder]

I'm looking at John's Blueprint CD (Thank You, Sir!) and I find it puzzling that DWM (and the other P-08 contractors) used 20tpi for their 18mm barrel thread (and 55�º for the thread angle instead of 60�º)...

20tpi isn't a metric size; John's print clearly shows that the thread pitch is 1.270mm...which works out to 0.04999985in...for comparison, 20tpi is 0.050in...Too close to be coincidence...

And it's not just Germany...The Swedish/Finnish Lahti shown in the first post also uses an 18mm x 20tpi thread...

Does anyone know why the Europeans would use an inch thread pitch??? The closest Metric thread pitch is 1.25mm...Which is quite common...and works out to 0.04921245in...Close, but no cigar...

On an unrelated note, while digging through my parts boxes from the '80's, I noticed that I have one of my home-made 150mm barrels lying around...It's been shot, and I can see some marks from the breech block, but I have no idea why it's still here...the two Lugers I owned back in the mid-'90's both had 150mm barrels on them when I sold them...

I guess it's true...A mind is a terrible thing to waste...