There is a long history of sub-caliber training rifles—rifles that allowed for low recoil and reduced-range training. Given the cost of centerfire ammunition, the allure of .22 LR as a training option should be obvious. And to fill that niche, Heckler & Koch (HK) has a gem. The manufacturer has taken its outstanding HK416 platform and, in partnership with Umarex, produced it in .22 LR. Not just another AR-15 chambered in .22 LR, the hardware and furniture of the HK416 rimfire are exact copies of the HK416 in 5.56 NATO. This makes the aforementioned ideal for using it as a sub-caliber trainer for the centerfire model.
The upper and lower receivers are anodized aluminum. The RIS (rail interface system) handguard has a top rail aligned with the receiver rail, creating a monolithic top rail for optics and accessory mounting. It is a MIL-STD 1913 (aka Picatinny) rail, and the accessory slots are M-Lok compatible. On top, HK has installed a set of folding sights. They are usable, but they are not exact copies of the HK sights one might expect, instead looking much like Magpul backup sights (but they are not made by Magpul).
The stock is telescoping, with six positions, so it can easily be adjusted to accommodate shooters of all sizes. The pistol grip has a storage compartment in it, and the safety/selector rotates 90 degrees from “safe” to “fire” and back.
The barrel is 16.1 inches long, so it is a standard carbine. It is threaded 1⁄2x28 tpi and comes with a flash hider. You can readily remove the flash hider and install a sound suppressor, should you wish. The ejection port has a working dustcover, and the rifle locks rearward when empty. An interesting aspect of AR-15s chambered in .22 LR is that the barrel and chamber are set back from the usual location on the centerfire versions. The breechface of the HK (like all ARs in .22 LR) can be seen in the ejection port. This means that a rimfire AR is actually .75- to 1-inch shorter in overall length compared with a centerfire version. The barrel exterior has a Carl Walther match liner, and accuracy testing showed that “match” is not just a marketing term.
The HK barrel is contoured to have the locating groove on it that an M4 barrel would have, for securing an M203 grenade launcher in place. Not that there are many of those to be found, nor needed on a rimfire trainer, but the HK416 Rimfire is meant to appear exactly like the centerfire model. This also carries over to the gas block, which the rimfire version does not need, being a straight blowback.
It feeds from magazines that are externally similar in size to 5.56 NATO magazines. They fit into the same-size magazine well, but have their internals shaped to hold and feed .22 LR ammunition. They are constructed of durable polymer and are readily distinguished from 5.56 magazines by the rimfire feed lips sticking up out of the polymer shell. The magazines hold 10, 20 or 30 rounds of .22 LR. The HK magazines (other AR-15 rimfire magazines do not fit the 416 rimfire) lock the bolt open when the last round is fired.
Both the upper and lower receivers have been designed and proportioned such that they will not accept other AR receivers. You cannot buy the HK416 Rimfire, and then drop a centerfire upper on it, nor swap your HK416 Rimfire upper onto another lower. The barrel and bolt are both serial-numbered to the lower receiver.
The similarity of the 416 Rimfire to the centerfire version does not extend to the bolt stop and forward assist. Both are inoperative, and HK/Umarex made the forward assist movable but inactive, and the bolt stop an immovable cosmetic detail. Also, the takedown pins are not captured, and will come out as separate parts when the rifle is disassembled.
In testing, for checking basic reliability, I mounted an EOTech HWS. The top rail is the correct dimension, and the sight clamped on with no problems. Once zeroed, the HK416 Rimfire fed fired and ejected all the ammo tested. The trigger pull was quite heavy, measuring an even 9 pounds of pull. Even with that pull weight, the HK 416 Rimfire wanted to shoot small groups.
As a money-saving trainer and to start new shooters, the HK416 Rimfire shows great promise, promise an adjustable trigger would fulfill.