A 12-gauge shotgun, by the way, is 18.5 mm or .73 caliber, and so-called Frag-12 explosive ammo already exists — as this video demonstrates.

The XM25 launches its 25 × 40 mm grenade at 210 m/s — about half a pistol round’s velocity — and its effective range is listed as 500 m for point targets, 700 m for area targets.

The XM109 “payload rifle” — a modified .50-caliber sniper rifle — launches its 25 × 59 mm shell at 425 m/s, and its effective range is listed as 2,000 m, presumably against vehicle-sized targets. Its box magazine holds five rounds — rather than 10 rounds of .50 — that sound quite effective:

The centerpiece of the XM-109 system is the 25mm HEDP ammunition it fires. A scaled down derivative of the low velocity 30mm HEDP M789 ammunition fired by the AH-64 Apache attack helicopter, the MX-109′s 25mm ammunition has been judged to be 2.5 times more effective at destroying targets than a .50 caliber armor-piercing round. It is expected that this ammunition can penetrate nearly 40mm (an inch and a half) of armor plating at 500 meters, or blast open doors from around the corner. In other words, it gives the Soldier breaching capability on fortified positions, while minimizing exposure to enemy fire, thanks to its effectiveness at greater distances.

So I can definitely imagine a smaller, lighter “payload rifle” with an effective range of 800 m against point targets, able to blast through most cover, yet safe to use at (fairly) close range.

Traditional grenade-launchers are much more like light mortars — low rate of fire (compared to an assault rifle), low-velocity round with a loopy trajectory, big blast radius (compared to a bullet), etc. — while “payload rifles” are more like ordinary rifles with fewer, heavier rounds.

So a 20-mm higher-velocity grenade-launcher would be accurate to 800 m? One of the drawbacks of a grenade-launcher is you can’t use it at close quarters. In this system you’re envisioning what do soldiers use for that, an under-barrel sub-machine-gun?

Or if the grenade is DIME perhaps a bayonet would suffice, lol.

Yes, my last paragraph was referring to smaller-caliber grenade-launchers, like the XM25 — and the Russians’ simpler 30-mm AGS-17 and AGS-30 launchers. Any grenade-launcher design trades off payload (and thus blast radius) against velocity (and thus distance and accuracy), and most current designs lean toward a relatively big 40-mm grenade lobbed at relatively low velocity, like a very light mortar. Another alternative would be to shoot a small 20-mm grenade at relatively high velocity, more like a light cannon. If our troops can consistently put rifle rounds within a meter of their target, then a single round with a one-meter kill radius might be worth dozens, hundreds, or even thousands of rifle rounds. It might obviate the need to suppress and then maneuver in order to neutralize.

Is your last paragraph a reference to the XM25? Are you saying the basic role of infantry is changing and that weapons like the XM-25 is restoring the balance infantry defense and offensive power?