Saw an ad years ago in Shotgun News for them, way back when Harris Gunworks was still around. Like the title says, it mounted under AR barrels like a 203, and I think it operated in similar fashion. Like all other .50 builders they claimed recoil similar to a 12 gauge. Anyone ever actually see one, or shoot it? Always wondered what they were like. I only saw the ad one time.

That sounds right. As I remember it, it was a stainless barrel, not sure if there was a pistol grip or you just used the mag like with a regular launcher. Seemed like an interesting idea but lousy execution. I think they were advertised for around $1200.

Sounds freaking cool.  Was it a DD or was it unregulated like a 37mm launcher?

All I know is from the one ad I saw and am going from memory. Don't remember mention of the barrel length, but maybe lacking a stock, if it had a 16" legal rifle length  barrel it would be measured by whatever the OAL of what it was mounted on was?

Or, maybe ATF said it would be a NFA item and that's why it never went beyond that ad. It's just one of those things I occasionally find myself wondering about and I happened to be browsing tech forums when I thought about it this time. Now, I at least know I didn't dream the ad(first response remembered it too) but for whatever reason they're apparently unavailable.

.410 surrounded by 6-9 .22s would be cool. Likely useless, but cool.

Some of my Contender barrels were bought for the same reason. I have a .12" 45-70 for deer hunting, but also bought a .45/.410, .357 maximum and .223 for no reason other than they were cheap. The Max was $170 shipped, with 150+ pieces of brass.