Jacketed vs. Plain Lead Bullets?

Apparently the preferred jacketed bullet for a Pardini in 32ACP has a diameter of .312" while plain lead bullets seem better suited at .314".  What is the reason for the difference in diameter for jacketed and plain lead bullets?  Does this also apply to bullets for 45ACP?

well, yes.

Jacketed bullets are typically groove diameter or close and lead bullets are generally +/- 0.001 over.   (Jacketed .45 ACP = 0.451; Lead .45 ACP = 0.452) 

This is a rule of thumb.

And add to this that the range of ".32" barrel / groove dimensions is pretty varied as well, you get to the point that you need to know exactly what you have (in the bore / groove diameter department). 

As you know: 

An engineer is just a rule of thumb physicist.
A philosopher is a physicist with no thumbs.

CR

(thanks fc60!)

Greetings,

The Pardini 32 ACP barrels are quite uniform internally. They gauge between 0.3135" and 0.3145" groove diameter and 0.305"-0.306" bore diameter.

Why does a jacketed bullet of 0.311" or 0.312" shoot so well in the 0.314" barrels? I have not been able to sort this out. It is fruitless to write to the "Big" ammo companies to ask as they never reply.

Testing swaged Lead bullets in a 0.314" Pardini barrel, I get better groups with the 0.314" diameter. 0.312" swaged Lead bullets shoot ten ring, at best.

I have written to PardiniUSA suggesting that Italy machine the barrels with a smaller groove diameter with little success.

Cheers,

Dave

fc60 wrote:Greetings,

The Pardini 32 ACP barrels are quite uniform internally. They gauge between 0.3135" and 0.3145" groove diameter and 0.305"-0.306" bore diameter.

Why does a jacketed bullet of 0.311" or 0.312" shoot so well in the 0.314" barrels? I have not been able to sort this out. It is fruitless to write to the "Big" ammo companies to ask as they never reply.

Testing swaged Lead bullets in a 0.314" Pardini barrel, I get better groups with the 0.314" diameter. 0.312" swaged Lead bullets shoot ten ring, at best.

I have written to PardiniUSA suggesting that Italy machine the barrels with a smaller groove diameter with little success.

Cheers,

Dave

Since the jacketed bullets obviously have a harder shell I wonder whether there is a point when the hardness of a lead only bullet begins to match the performance of a jacketed bullet.  Maybe a harder bullet doesn't need to have full engagement with the grooves of the barrel to achieve the proper spin dynamics.