I read somewhere that some Sigs don't like weak 115 grain range ammo. And that 125 is preferred.

I have shot a 9mm P320 Compact FDE rental at my local range and used cheap Remington 115 range ammo. The P320 Compact shot it accurately and without malfunctions. I also ran some Federal 115 through it and it did fine as well. Of course, this was a range rental and the RO at the counter said it had over 6,000 rounds through it. I've tried the gun out twice and experienced no issues with 115 grain range ammo.

Just wondering if 125 grain is recommended to break in the P320 Compact for a certain number of rounds before using 115 grain.

Any standard 9mm ammo from 115 grain up to 147 will work fine in the p320 from day 1. There is no break in period with the p320 and if you have problems with a new one should probably call Sig. I’m not aware of any service type pistols (Glocks, S&W M&Ps, etc.) that require a break in period. All should be ready to go out of the box.

To back up what jtd85 posted, I've shot a few hundred rounds of 115, 124, and 147 gr 9mm through mine, new and remanufactured. No hiccups at all, and all shot accurately. I haven't tried any hollow points yet though.

I bought three P320 /9mm pistols before the upgrade, two compacts and one subcompact. As with all my 9mm pistols, I shot a mixture of factory 115-124-147gr (no +p in my guns) to test them. Not a single malfunction. Then I shot a mixture of factory jhp. Not a single malfunction. I carry with only 147gr jhp.

When returned from the upgrade, I did an abbreviated re-test since so many people were concerned about how the upgrade would negatively effect the platform. Not a single malfunction.

If only SIG made cars, or electrical appliances...

I have not had any issues with 115 grain 9 mm Luger ammunition in my P320 compact or my P250 subcompact.

I have about 500 rounds through mine, including 115-grain, no stoppages. My carry load is Federal 9BP (its stocking number), a 115-grain standard pressure hollow-point.

I have been shooting Winchester USA 115 gr. white box and American Eagle 115 gr. in my full size P320 from day one with no issues at all.

Thanks for the replies. Is everyone satisfied with the P320 after the upgrade. I've seen varying reports, but most seem positive.

I'm interested in the Compact.

I've been using the 9mm 124 NATO from Men, a German company, SGAmmo.com has had it for good price all year long. I started getting 200 round battle packs and just got 1k in an ammo can.

I've found it clean shooting and accurate, no issues in my P320 C or Beretta/Wilson ComTac.

No difference at all in functionality from before and after the upgrade.
In fact I think my trigger is a little better now since the UG.

Both of mine eat everything without a problem, triggers both slightly better upon return from upgrade.

All my SIG 9mm pistols will shoot anything. Get what's least expensive in your area and shoot away.