When the .22 WMR was unveiled in 1959, magnums were all the rage. And it indeed proved to be a significant step up from the .22LR, operating at a higher pressure and delivering jacketed, not soft-lead, bullets at nearly 2,000 fps.

It also proved to be a tough nut to wrestle into an autoloading rifle, if I may mix my metaphors. With a chamber pressure of 25,600 PSI, it is about as much as you can handle in a locked action designed for the .22LR. But manufacturers, ever anxious to deliver product to the shooter, worked to make it work. Which was all fine and dandy until Hornady came up with the .17 HMR. To distill it to its essence, it is a .22 WMR necked down to .17. It has the same overall length and the same operating pressure. But making it work in a self-loading rifle proved problematic.

You see, pressure isn’t everything. You need bullet mass to work the blowback action of rimfire autoloading rifles, and the .17 HMR, with bullets weighing from a mere slip of 15.5 grains up to a “hefty” 20 grains, offers half the bullet mass of the .22 WMR at best. But you can’t just make the bolt lighter to accommodate the lowered bullet mass, as you still have the pressure to deal with. Plus, combining a bottlenecked case with a blowback action is just asking for trouble. One sign of early opening is stretched case shoulders.

If you simply increase bolt mass, the mass of the bolt, on feeding, may crush your loaded round against the feed ramp. Or short-stroke. A heavier action spring, to delay opening, may also cause short-stroking if the round doesn’t have enough oomph to overcome the spring.

For the manufacturers making bolt-action rifles, adding the .17 HMR to the lineup was simple: A new barrel, with the appropriate chamber and bore, is all they needed. The rest — receiver, magazine, bolt — are identical in dimension, and the back thrust the bolt experiences is also the same. No one out there can work a bolt fast enough to create a problem with brass not having contracted (short of excessive pressures) or with residual pressure causing case-stretch problems.

However, any self-loading action is a delicate balance of dynamic forces. The blowbacks are more so, and asking an action to smoothly handle the .17 HMR is enough to make any rifle designer stay up late at night.

A designer who takes such things in stride is Bill Alexander of Alexander Arms. Not only has he come up with a self-loading .17 HMR that works, he has clothed it in an AR receiver. The heart is a stainless barrel in .17 caliber with a twist of 1:10. The rifle he sent me features the spiral fluted exterior. There were details of this rifle that puzzled me, but they were cleared up when I talked to Bill. On the front end, the barrel features the common ½-28X thread that all .223 rifles use, so you can put on any muzzlebrake or flash hider you desire. I have to warn you that doing so will be almost entirely a cosmetic exercise. The .17 HMR neither has enough muzzle flash to warrant a flash hider nor enough gas pressure at the muzzle to drive a brake or compensator. But it is a snazzy crown protector.

When I talked to Bill about this, he remarked that “the .17 HMR project took more time than the .50 Beowulf and the 6.5 Grendel combined.” And the rifle I had? Not just an early rifle, but the first prototype. It worked like a charm, which is why it was sent to me for testing right away. And its promise had Bill working overtime, because prototypes No. 2, 3 and 4 were all demon-children.

The bolt is made of ETD 150 steel, a chrome-moly manganese-silicon alloy that is easily worked, and Bill loves it. “ETD 150 is essentially aerospace-grade prehardened 4140 and a joy to work with.” In the AA .17 HMR, the bolt is also chrome-plated. Well, the new ones are, but my prototype was not. If you have a host of rimfire-converted ARs, you don’t have to worry about getting this one confused, because the bolt is clearly marked “17-HMR” through the ejection port. While the .17 (and .22) HMR runs cleaner than its .22LR predecessor, all blowback actions run dirty, and having a slick, easy-to-clean bolt is welcome. The bolt is also much heavier than that of its .22LR cousins, as befitting the .17 HMR chambering. The extractor is hardened stainless, again an easy-to-clean part on a design that will get grubby after you’ve used it to relentlessly hose varmints in the back 40.

The desire to have an easy-to-clean bolt led to it being hard-chromed in production. This resulted in magazine problems (didn’t I say the .17 is a handful?). It seemed that the lower friction of the chromed bolt required a heavier magazine spring to keep up with the bolt cycle rate.

The rifle Bill sent me featured a carbine buffer tube, but it can be rebuilt (or come from Alexander Arms) to a solid A2 stock if you wish. The recoil spring is inside a sleeve in the buffer tube, another approach Bill took to make the .17 reliable and adaptable to any lower. It also precludes using a .223/5.56 upper with the .17 buffer assembly installed — a clever move on Bill’s part. You have choices on the forearm. One is the AA mid-length free-float tube composed of G10/FR4 composite with a big aluminum barrel nut holding things together. If your varmint-slaughtering tool of choice simply has to have an acre of “rail estate,” then you want the Mk 3 mid-length monolithic rail receiver from Alexander Arms instead.

The extractor on a rimfire magnum leads a hard life. “The extractor works hard to pull that long case out of the chamber, and we started with 416 stainless. But it soon became clear we needed to go with 17-4 precipitation-hardened stainless, a tougher and harder alloy.”

One last detail of the upper is the firing pin. Hefty to withstand many cartons of ammo, it uses a return spring. Rimfire rifles can be quite sensitive to firing-pin impact, and you want immediate and full ignition for best accuracy. However, you can’t have a free-floating firing pin in there, at least not one of any significant weight, so Bill took a sturdy firing pin and designed the bolt to have a firing-pin return spring in it to control any firing-pin bounce on feeding.

In the lower, the .17 HMR magazines require an adapter block, or magazine block, in order to fit. The Alexander Arms adaptation uses a caliber-specific extended latch to hold the magazine itself. The adapter block is held in mainly by the magazine catch (as with some conversions), but the new catch has an extra step to keep the block in place. Also, there is a set screw to lock the block in place. That screw eliminates block wobble and ensures reliable feeding.

The .17 HMR magazines are made of molded acrylic, a very hard plastic but one that molds to precise dimensions. And it’s cheap, too. You see, the .17 is very sensitive to feed-lip dimensions. If the magazine wears, you lose reliability. Again, Bill was clear on this point. “I could make magazines out of tool steel, and they’d still wear. This way, they are precise, but if or when they wear, you can buy new ones for a pittance.” And yes, he is planning on making high-cap mags. When I called him on his cell phone, he was at the range testing.

The conversion is designed so you can install the .17 HMR upper on your lower, plug in the adapter block and magazine catch, and the buffer-tube spring assembly, and go to work. You use the recoil-spring system of the conversion that is appropriate for the buffer tube (carbine or rifle) on your lower. That means that if you have a custom trigger assembly in your lower, tuned for a clean, crisp target trigger pull, it is now available for your varmint-shooting expeditions.

To add to the one-of-a-kind nature of the rifle, Bill sent his first prototype installed on the first .50 Grendel-marked lower AA made. With box-stock fire-control parts, the lower worked just fine.

Gear is fun, and the details matter, but what it all comes down to is shooting. And there I have to report almost complete success. First off, the .17 HMR is a varmint-shooting cartridge. It has no other reason to exist, as it is far too expensive to use as a plinker. I mean, for the cost of .17 HMR (around $200/thousand rounds), you could just as easily be shooting reloaded .223. (Sorry, Hornady, but that’s the truth.) If it is going to be a varmint round, it had better well be accurate.

Well, here you have no fears. Rimfire rifles are notorious for being picky about ammo and very particular about how they are fired. The jacketed bullets of the .17 make it less so, but they can still be touchy. I found that out my first day at the range with the Alexander .17, as I was scattering shots all over the place. I knew it couldn’t be the ammo, as I had just received a brand-new shipment from Hornady. So I shot chrono info and function-tested the Alexander rifle, then came back another day. That day, with no coffee and good weather, I got back to good technique and shot very nice groups indeed. The little .17-caliber bullets are quite wind-sensitive, but my range is in a valley, and with no wind I was shooting one MOA with it. The Bushnell 10X scope, held in place by an American Defense QD Quik-Lock mount, made it easy. Oh, Bill loves the Bushnell 10X. “You can’t break them. I’ve shot truckloads of ammo under the Bushnells I have, and none has given me any problems.”

Recoil? You can’t be serious. I could see the bullet holes appear in the target, and when I was whacking odd bits of debris on the backstop, I could easily watch the impact through the view of the Bushnell scope. Follow-up shots on missed varmints can easily be applied, although your success rate will suffer, as they’ll probably be moving by then.

In all that time, I had one failure to feed, and that came with the 15.5-grain NT load. The NT means “no toxins,” as in “no lead.” A 15-grain lead-free bullet is a challenge both ballistically (they shot well) and functionally. When I told Bill, he remarked, “Ah, the 15-grain bullet, the nemesis of the .17 HMR. That one gave me more trouble than the rest combined.” My sole malfunction was a bolt-over-base failure to feed that jammed the bottom lip of the bolt into the case. Which is exactly the kind of problem the (new) heavier magazine springs will preclude. And since I’m not likely to be charged by a wounded varmint, and it happened early on in the break-in period and never recurred, I’m not worried. I’m not sure I’d go so far as to use it on critters larger than the various families of rodentia, but for those it excels.

I’m not so sure that the upper, as just an upper to swap around on rifles, will be the one you want. All AR owners, once they’ve had a few range sessions under their belt, abandon the idea of one lower and multiple uppers. That is Bill’s plan and mine, too. “The guy who wants to go shooting varmints isn’t going to settle for a mil-spec trigger on his one-and-only lower. We’ll be making complete rifles straight away.” And that is my plan, too: to get a complete Alexander Arms rifle in .17 HMR and order several cubic feet of ammo from Hornady.

No point in doing things in half measures, even if it seems like a half-pint cartridge.

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