Refleks said:

Yes I seem to recall the prox ammo being 30x173, they fired 30x113 against metal containers and they looked like HEDP

They did fire 30x113 prox ammo at quadcopters, so it's not impossible that the airbursts in question were 30x113 XM1211.

Hmm.  It just occurred to me that the airbursts in question happened a few feet from the embankment behind the trench.

Is it possible (or probable?) for the proximity fuze to have sensed the dirt embankment, thereby initiating those airbursts?

More info, there are 2x types of airburst 30x113 being developed.

https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2022/future/Tues_GM_PMMAS_Santamaria.pdf

Also development for x113 and x173mm airburst is prompting more development in fusing:

M789 HEDP was modified to include a percussion primer and self-destruct fuze feature to provide dual-purpose capability while reducing the threat of collateral damage and unexploded ordnance. XM1198 HEDP-SD provides hit-to-kill UAS capability while maintaining armor defeat, and XM1211 HEP provides proximity airburst against drones and personnel.

XM1198 was developed, tested and approved for an urgent materiel release to support an initial 2021 fielding. XM1211 has a single mode proximity fuze & is undergoing validation for UMR to field this year.

XM1223 is the developmental replacement for XM1198 & XM1211. It has a multimode proximity fuze with proximity airburst, gated proximity and point detonating functions to allow one round to be effective against uas, infantry in defilade, and vehicles. This matters because the LW30/M230/XM914E1 is a single feed chaingun. Swapping ammo natures is not possible on the fly.

source: https://asc.army.mil/web/news-incremental-advances/

Edit: there may be 3 30x113B proximity fuzed rounds - XM1206 HEDP-AB is in EMD this year for PM Apache and FMS. There are 2 30x173 AB rounds, MK310 programmable fuzed airburst was fielded via UMR in 2021, XM1182 HEAB-T is due for milestone C in 2023. The source is unclear whether these AB rounds are prox fuzed or time fuzed.

https://asc.army.mil/web/portfolio-item/ammunition-medium-caliber/

20x102 MP rounds are to be developed for FVL (FARA is still part of FVL portfolio) in 2023. Currently USArmy only has 1 fielded 20mm nature, M940 MPT-SD, presumably the development will involve removing the SD feature for a2g use and, perhaps, further aeroballistic optimisation. 
https://www.gd-ots.com/wp-content/uploads/2021/12/20mm-M940-MPT-SD-2021.pdf

DavidPawley said:

XM1223 is the developmental replacement for XM1198 & XM1211. It has a multimode proximity fuze with proximity airburst, gated proximity and point detonating functions to allow one round to be effective against uas, infantry in defilade, and vehicles.

Great info. So the XM1223 is really the ideal load then, and has the hoped for gated prox for ground to ground use.

Previously there had been concern about the frag effect of x113, and work to improve its lethality, possibly by introducing a fragmentation liner inside the shell. Or ideally creating a PFF design.

I wonder whether the XM1223 will also feature some frag optimization? That would be good not just for anti personel, but also help increase the chance of incapacitating drones. 

Tony really called it in his article on the subject years ago suggesting the 30x113 could be the sweet spot for light armored vehicle and APC armament.

https://www.quarryhs.co.uk/CANNON2.pdf

The FVL ammunition is PGU28A/B. I guess the development is to qualify and type classify it for Army service.

DavidPawley said:

The FVL ammunition is PGU28A/B

I'm still really surprised they are going with 20mm, especially in light of these new high performance 30x113 rounds. 

gatnerd said:

I'm still really surprised they are going with 20mm, especially in light of these new high performance 30x113 rounds. 

For air-to-air and air-to-ground applications, the high MV of the 20 mm provides better hit probability.

Do helicopters get in much air to air fighting? 

For air to ground, does the increased hit probability of the higher velocity 20mm overcome the greater lethal radius + airburst of the 30mm? 

In terms of air to air, one of the things I've thought about since the iranian drones started showing up in Ukraine is that a Apache/other helicopter with airburst 30mm would actually make for a pretty decent mobile air defense against drones. 

Maybe it's just institutional inertia - USMC uses 20mm in their AH-1.

Or weight saving, as 20mm ammo is lighter.

In any case, a cannon is the last of the last options for a helo in most cases. 20mm will probably do the trick when rocktes and missiles are too much for any reason.