But tomorrow, Madame, I will be sober

We despaired in a recent post that carbines of the AR15 family can get a new lease on service with Uncle Sugar if only the cartridge were changed to something that delivers lethality at greater range. One new cartridge is under serious consideration by our esteemed Uncle, another has been proposed, both fitting neatly within the physical constraints of the existing carbine and magazine, needing little more than a new barrel, bolt, and magazine follower to lose the "poodle shooter" pejorative.

Either the 6.5mm Grendel (the preferred solution here at WUTT!) or the 6.8mm Remington SPC (the likely successor) would be a major step forward.

But as the borrowed Churchill quip implies, we can change the caliber but the carbine will still be an AR15. It taps propellant gas from the barrel, and ducts it half the length of the weapon back to a chamber inside the bolt carrier to operate the action. This reduces the weight and parts count of the weapon, but dumps propellant gas inside the action where it can foul it and cause malfunctions.

The AR15 also uses a cocking handle that rides inside the top of the upper receiver. It is difficult to use this cocking handle with the non-firing hand while the firing hand keeps a consistent grip. The movement of this control also interferes with placement of a cheekrest. Aftermarket upper receivers are available with cocking handles on the left side of the receiver, like the FAL's, instead of on top at the rear.

Rather than replace the AR15 family carbines already in Uncle's arsenal, we propose instead to refit them, both to change the cartridge to a non-poodle shooter, and to remove these two design details. Mr and Mrs Taxpayer may thank WUTT! for the tens of millions of dollars saved.

The existing upper receiver can be retained, if has the rails for the removable carry handle.

Everything from the upper receiver forward goes away. The new barrel bears a block, in place of the front sight, that offers short Picatinny rails at 12, 3, 6, and 9 o'clock around the barrel's circumference. A gas piston inside the block taps the propellant gas and points it rearward. The rails offer ample space to mount sights, lights, designators, even a recoil- or muzzle-operated digital camera.

Instead of the loooooong gas tube sprouting from the gas block, an operating rod with a cylinder in its front end mates to the piston at the front, and passes into the upper receiver at the rear. The rear fits inside the bolt carrier key. Heckler and Koch have already designed this part and offer it as a retrofit for M4 carbines.

A replacement upper handguard has room for the operating rod, and includes a folding cocking handle. This handle can swing either to right or to left, to grab the operating rod and cycle it. The handle does not reciprocate with the operating rod.

A rear block surrounds the barrel immediately in front of the gland nut that tightens the barrel to the upper receiver. It has a short Picatinny rail at 12 o'clock, and a channel under that to take the operating rod and guide it, and retain the upper handguard. At 6 o'clock, it has hardpoints that lock bipod legs in place.

The lower handguard looks just like a lower handguard, but it is split into quarters, right and left. These are extensible legs of a bipod. The legs hinge where they attach to the front sight block.

A vertical foregrip, a GL, or a shotgun can be installed in place of the lower handguard, of course.

Important: the Picatinny rails do not surround the barrel along most of its length like on the current M4A1. The rails, and the handguards fastened to them, trap too much heat on the barrel. In prolonged action, the barrel gets hot enough to ignite a cartridge as soon as it's chambered, known as a cook-off.

The receiver-mounted cocking handle is removed, and a plastic plug installs in its place. Ears from the plug reach around to the rear of the sight rail on the upper receiver, to fasten tightly there. The plug provides a press-fit between upper and lower receivers when they are closed, and could be fashioned as a flip-up reserve rear sight, calibrated for the new caliber.