Was able to shoot the P320 in both 9mm and .45 today and the grip on the .45 was so much nicer and fit my hand like a glove.
Its my understanding that the P320 in 9mm and .45 come standard with Medium grip.
Would getting the Large grip for the 9mm make it like the medium grip in .45?
Does anyone have both and able to measure the circumference?

Looking at Osage County Guns site says the 9mm Large is 5.9"/150mm and the 45 medium is 5.7"/145mm. But looking at the sizes on the site they all are identical between all calibers.

I think the only difference between grip calibers is the size of the magwell. all exterior dimensions should be the same.

I switched to a large grip, and it helped a lot. At an Operation Specific training class I was told that the large would be best for those with medium hands as well as large hands.

However, both grips are too round. I flattened the sides with a belt sander, and that helped much. The X-5 Carry grip has nice flat sides. Right now Sig is selling the X-5 grip in Medium, hopefully in a couple of months it will be available in Large.

I did some measuring and there is a slight difference between the 2 M grip frames.

Ordered the Large for the 9mm and will see how that works out.