Gun pr0n dreamy dreams

First, I always wanted one of these, more than I lusted for a SPAS 12, say.
The High Standard 10B, a bullpup shotgun. I'm borrowing this photo from a Gunbroker auction, sorry if that offends.

If I were a lunatic independently-wealthy tinkering gunsmith, I'd apply the 10B treatment to a newer semi-auto, and extend that tubular magazine right out to the muzzle. Then I'd package the treatment as a kit for the hobbyist to mount on his own. I don't know enough about modern selfloading shotguns to pick the right one. Bleg?

Meanwhile, on the AR front:

With everybody except me offering a gas-piston AR clone design, the criticisms of the gas piston versus direct gas impingement are emerging, and the most cogent I've heard is this: the direct impingement system applies force exactly along the axis of the bore, breechbolt, and bolt carrier. All are in balance.

A piston offsets that force above the bore axis, causing the bolt carrier to tilt and shave away the soft aluminum of the AR's receiver pieces. A full-auto pistonized AR will grind itself to swarf in one firefight. AKs, in comparison, have rails that guide the bolt carrier and bolt in the needed direction; the offset force harms nothing.

If I were a lunatic independently-wealthy tinkering gunsmith, I'd solve that problem by integrating a steel supporting rail in the roof of the upper receiver. It would take the place of the cocking piece, and probably still function as one. The face of the bolt carrier that takes the force of the gas piston (no longer a "key") would be shaped to ride in that rail, and would not come down out of that rail unless the rail itself were extracted from the upper. The rail would have ample room for lubrication and for the accumulation of chum for the happy soldier to clean away. The bolt carrier would then have little or no surface on it to bear against the inside of the upper receiver---the rail handles all of that. No damage to aluminum receiver.

Whether this configuration would continue to use the existing buffer spring, buffer and buffer tube assembly is still undecided. Maybe the bolt carrier can be carved up to make room for recoil springs that fit within the upper receiver, like on the para FAL?