Logan Nye was an Army journalist and paratrooper in the 82nd Airborne Division, where he got to see the experimental XM-25 grenade-launcher in action:
I was a young public affairs sergeant assigned to an airborne brigade combat team, and we had one Stryker battalion attached to us that got the XM25 Counter Defilade Target Engagement (CDTE) System, commonly known as the “Punisher.” It was similar to the SSRS, but it carried a smaller round at 25mm or .98-caliber, closer to the Bolter. When it worked, it really worked: Shooters used a laser to gauge distance to a target, told the weapon how much farther the target was behind the cover, then fired. The round flew past the cover, detonated at the specified distance and generally ruined people’s days.
But it was expensive; each round cost $1,000 and was expected to drop to $35 or so in full production. And the system frequently failed. I photographed a sergeant major firing it in a “familiarization shoot” and something like eight rounds failed in a row. A military police soldier and I slowly counted the shots as I took photos, marking each time that another two weeks of our pay had gone downrange and failed to explode.
It was worse on patrols, where troops couldn’t count on the weapon in tough fights. It was risky to break cover to fire the weapon when it might take five or even 10 shots to get the burst. They obviously tried, but the troops in contact reports would come across the brigade chat system, saying that they’d expended 10 or 20 rounds for zero enemy casualties. It’s no wonder the Army eventually abandoned the CDTE effort in 2018.
The new SSRS looks less complicated:
Key to the Barrett SSRS’s design is its user-friendly, assault-rifle-based structure. The weapon features a butt stock at the rear, an [sic] five rounds ammunition magazine in the center, and a barrel length of 305mm. The grenade launcher is compact and versatile with an overall length of 861mm and weighing just 6.3kg. It can fire various ammunition, including airburst rounds, giving soldiers a crucial advantage on the battlefield.
A big, heavy, unreliable weapon has multiple strikes against it, but a small, light, reliable version might hit the sweet spot, where its small projectile can be launched at high enough velocity for accurate more-or-less direct fire, but the payload is big enough to kill nearby gunmen with a not-quite-direct hit.
Somewhat relevant: the XM-29 was humorously reviewed by a fat electrician.
https://youtu.be/wvV6u3dchkc?t=120
He claims it was doomed because explosive bullets had been banned in 1868, but I don’t really think that’s a persuasive argument.
Justin Taylor discusses the SSRS and other grenade-launchers in his video The Newest Arms Race You’ve Never Heard Of.