Pardini 32acp barrel questions

What is the ideal twist rate for the Pardini 32 acp or even the 32swl? Specifically for the 50 yard line. 

I read online that 1-16 is stock but the custom barrels are 1-10? 
-J

highly highly doubt that it is 1-16

I read on target talk: 

Reply from Pardini Italy

HP New Bullseye
Bore: .313
Length: 120mm = 4.7244 inches
Twist: 6D x 450mm = 1 x 17.7165 inches

cjon600 wrote:I read on target talk: 

Reply from Pardini Italy

HP New Bullseye
Bore: .313
Length: 120mm = 4.7244 inches
Twist: 6D x 450mm = 1 x 17.7165 inches

looks more correct except that bore... that is probably the groove diameter

Don't understand the twist.  What is meant by 6D x 450mm???  450mm is 17"+, but what is the 6D?

6 groove maybe?