The 320 and the 365 are 2 entirely different pistols.. see the factory specs below from the SIG web site..https://www.sigsauer.com/store/p365-nitron-micro-compact.html

The 365 has considerably smaller dimensions compared to the 320 Model's I have shot...the 320 has a much fuller grip and easier to control, even in a 9mm, the 365 is snappy to fire..has a very narrow grip..thin.. have to keep a good grip on it for fast follow up shots..

Went to the range again today and ran another 150 rounds through a 320 Compact doing drills..was very happy with the results..frankly was shooting it nearly as well as my Glock 34 that I probably have 4-5000 rounds through now..

I owned a 365 for one week..bought it new--took it to the gun range--it would not fire..broken firing pin from the factory..took it back and traded it for a Glock 43..have now put a lot of rounds through the 43 without any failure of any kind..

The 365 will be a great concealed carry handgun once the bugs are worked out..the large capacity in that small of a handgun is awesome..but will not put my families safety in a weapon with this issue for the time being.. I am not the only one who has had issues with new guns right from the factory..reading on the net, there is a definite quality control issue of some sort..

As for the 320, one of those will be in my possession within the next week.. the trigger is really really good along with the general ergonomics that fit me very well..

BARREL LENGTH
3.6 in (91 mm)
OVERALL LENGTH
6.7 in (170 mm)
OVERALL WIDTH
1.3 in (33 mm)
HEIGHT
4.7 in (119 mm)
WEIGHT
24.9 oz (706 g)
DETAILS
The P320 Subcompact offers a smooth, crisp trigger to make any shooter more accurate, an intuitive, 3-point takedown and unmatched modularity to fit any shooter and any situation. Its subcompact frame is ideal for concealment or small-handed shooters. This modular, striker-fired pistol features a subcompact grip, subcompact slide, choice of contrast or SIGLITE Night Sights, and now, optional accessory rail. Available calibers include 9mm and .40S&W.

OVERALL LENGTH
5.8 in (147 mm)
OVERALL WIDTH
1.0 in (26 mm)
HEIGHT
4.3 in (109 mm)
WEIGHT
17.8 oz (500 g)
DETAILS
Introducing the game changing P365. Micro-compact everyday carry size with unprecedented 10+1 full-size capacity. The P365 is striker-fired, with the clean crisp trigger pull you expect from a SIG. Lightweight and easy to conceal, the P365 is chambered in 9mm and is rated for +P ammunition. Included standard are XRAY3 Day/Night sights, a 10-round flush fit magazine, and a 10-round extended magazine. An optional 12-round extended magazine allows you to bring the total capacity to 13 rounds. The new