December 14, 2015
By Layne Simpson
When adding the .17 Winchester Super Magnum chambering to its AR-15 style rifle during early 2014, Franklin Armory became the first company to offer a gas-operated semiautomatic chambered for that cartridge: the F17 L. The original rifle was a direct gas impingement design, but a few months later the switch was made to piston driven.
Upper and lower receivers of the Franklin Armory F17 L are machined from billets of 7075-T6 aluminum and then given a hardcoat anodized finish with an olive drab coloration. A Picatinny rail runs the full length of the flat-top receiver. Play between upper and lower assemblies is minimized by turning an adjustable tension screw. The free-floating aluminum handguard has M-Lok receptacles up front, and in addition to a checkered gripping surface, it has an integral bipod/tripod adaptor plate.
A flared magazine well makes for snag-free reloads, and the integral cold-weather trigger guard is plenty roomy for a gloved finger. Just beyond the trigger guard opening is a serrated memory index point for the shooting finger. Other features include Magpul MOE stock, Ergo SureGrip grip, quick-detachable sling-swivel mounts and custom-tuned trigger. The familiar hinged ejection port cover and case deflector are also there. At 0.545 inch, the ejection port is a bit taller than commonly seen on 5.56/.223 uppers.
The lower of the Franklin Armory F17 rifle evaluated for this report is marked "Multi Caliber," which means it is compatible with uppers in other calibers, including those offered by Franklin Armory. Those listed in the owner's manual include .204 Ruger, 5.56/.223, .223 WSSM, .243 WSSM, .25 WSSM, 6.5 Grendel, 6.8mm SPC, 7.62x39mm, .300 Blackout, and .450 Bushmaster.
Inside the F17
The .17 WSM uses a standard-tension action spring, but since the bolt carrier has less distance to travel to the rear for the short rimfire cartridge, its travel is shortened accordingly by the use of a buffer measuring a bit over 7 inches long. Those in my .223-caliber ARs are about an inch shorter.
A "Special Rimfire Warning" in the owner's manual spells out several precautions to be followed when using the forward assist. Ratchet notches in the body of the bolt carrier are limited in number to those required for the forward assist to function only at the very end of carrier travel where the bolt begins to engage the barrel extension lugs. This was purposely done to discourage the crushing of a live rimfire cartridge prior to the bolt moving into full battery. Should the forward assist of a particular rifle happen to be capable of forcing the carrier forward at any point short of that, the rifle should be returned to the factory immediately.
The forward assist of the Franklin Armory F17 L should never be used in an attempt to clear any type of feeding malfunction, such as a double-feed or a stovepipe jam. It is designed to be used in situations where slight resistance must be overcome in order to coax the extractor hook over the rim of a cartridge as the bolt moves into battery. Like most rifles of military design, AR-15s have a floating firing pin. For this reason a cartridge should not be manually loaded in the chamber and the bolt allowed to fly forward at full velocity. And since dropping the rifle muzzle-down on a hard surface could cause it to fire even with the safety engaged, the rifle is best carried with no cartridge in the chamber.
The firing pin of a centerfire rifle travels along the same axis as the primer in a centerfire cartridge, whereas the rim of a rimfire cartridge has to be struck off to the side of center. This is accomplished in the Franklin Armory rifle by utilizing a two-piece firing pin with the front section having an offset shape. With the exception of being shorter, the rear section looks about the same as any other AR-15 firing pin and is positioned at the center of the bolt. When struck by the hammer, it moves forward to strike the forward section located at the front of the bolt. The rear section is held in place by the familiar cotter pin-style retainer, while its companion up front is retained by the extractor.
The bolt carrier has standard AR-15 exterior dimensions, but with a body measuring 0.440 inch in diameter, the rimfire bolt is a bit smaller than is typical for a centerfire bolt. The reduction in diameter reduces the number of locking lugs to five, but not to worry as breech lockup is still far stronger than it has to be for the .17 WSM cartridge. To ease machining and to aid in unlocking, the tops of the lugs are rounded rather than flat.
The plunger-style ejector is positioned a bit closer to six o'clock than on a .223 bolt, and the firing pin is at one o'clock. Extractor locations are about the same, and since resistance to being extracted from a dirty chamber is less for a fired .17 WSM case than for a centerfire case, the extractor is not as heavy, nor is its claw as wide.
And, of course, the keys of the two bolt carriers differ. In the direct impingement system the key has a gas expansion chamber and is a separate part attached to the top of the carrier with two screws. An integral part of the carrier, the key in a piston system has no chamber since it serves only as a tappet (or impact lug) for the gas piston and to prevent carrier rotation within the receiver. Weights of the two bolt-carrier groups are close to the same — 10.8 ounces for the rimfire and 11.1 ounces for a centerfire. The carrier does not lock back on an empty magazine, but an engineered solution may change that when a new polymer magazine presently under development goes into production.
The 4140 chrome-moly bull barrel is 20 inches long and measures a robust 0.920 inch at the muzzle. Its six-groove rifling has a twist rate of 1:9 inches. An 11-degree crown with a deep counterbore at the muzzle protects the rifling from dings in the field. A salt bath nitride finish inside and out prevents rusting. It is also said to discourage powder and bullet jacket fouling, making the bore easier to keep clean.
Whereas chamber support of a rimless centerfire cartridge in an AR-15 barrel terminates a bit forward of its extractor groove, the chamber of the Franklin Armory F17 L fully supports a .17 WSM cartridge all the way back to the front of its rim. This is accomplished by machining the breechface of the barrel to leave a short extension of the chamber. Making the outside diameter of the extension a bit smaller than the rim diameter of the cartridge leaves enough overhanging to allow it to be grasped by the extractor. And with the exception of a narrow extractor notch machined through the boltface counterbore wall, the rim of a chambered cartridge is also enclosed by a solid ring of steel.
Maximum pressure for the .17 WSM is 33,000 psi, and though that's quite high for a rimfire cartridge, it is lower than for the .223 Remington. When developing the F17 L, Franklin Armory engineers found that while the pressure time curve of the rimfire cartridge is somewhat compatible with a carbine-length gas system, a pistol-length system with the gas port and gas block located about 3 inches closer to the chamber of the barrel works even better.
The single-stack magazine has the same exterior contours and dimensions as a 5.56/.223 magazine, so it's compatible with most AR-15 lowers. Due mainly to the rimmed case, the stacking characteristics of .17 WSM cartridges require a magazine curved in shape. The last five rounds are difficult to load with cold fingers, but where there is a will there is a better way, and here it is.
After four rounds are loaded, the follower is exposed through a window in the side of the magazine. With the magazine resting atop the bench, bullet end pointed forward and rear of magazine leaning against your leg, use a small screwdriver to press down on the follower just enough to allow each round to be slipped into the magazine. (This will become unnecessary when a newly designed magazine replete with follower depressor becomes available in a few months.) Capacity is 10 rounds, but a 20-round magazine is slated for early 2016.
A less expensive model called the Franklin Armory F17 V4 lacks some of the custom refinements of the Franklin Armory F17 L, but the biggest difference is 7075-T6 forged receivers in lieu of machined. The hardcoat anodized finish also has a black coloration. Mil-spec A2 stock and grip are standard. Factory accuracy requirements are the same as for the more expensive version. A "tactical" variant of the Franklin Armory F17 V4 is in the works. Called the Franklin Armory F17-M4, it will offer a 16-inch barrel and a collapsible stock.
The Shooting Results
It rarely happens in my part of the country, but range conditions were ideal with not even a light breeze during the three shooting sessions I spent with the Franklin Armory F17 L. Prior to shooting for accuracy, I broke in the barrel by scrubbing its bore with a bronze brush and Shooter's Choice powder solvent between each shot for the first 20 rounds. The bore was then cleaned every five shots for the next 25 rounds.
During the accuracy tests the rifle wore a Nikon 4-16X Monarch scope, and its bore was cleaned every 50 rounds. On hand was ammo from Hornady and Federal and two different manufacturing lots of the Winchester 20-grain load. Despite my best efforts, practically every one of the groups had a single flyer. Thinking the scope might be acting up, I tried another to no avail. Switching to a softer front rest produced the same results. Shooting the rifle with a light hold or a firm hold made no difference. Nothing I tried eliminated those darned flyers. Thinking I might be having two bad days in a row, another experienced shooter was asked to give the rifle a try. Accuracy remained the same. The trigger cannot be blamed because as AR-15s go, the one on the Franklin Armory F17 L would be difficult to improve.
Occasionally, the rifle would snuggle five bullets close together, and then each subsequent group in a string would have a flyer. Most of the time all groups had flyers. Group size increased rapidly as the barrel became hot, even though it was allowed to cool down every 25 shots. Group size also increased as powder fouling accumulated in the bore. Some of the smallest groups (including flyers) were fired from a cold barrel immediately after its bore had been cleaned. It was frustrating, considering that in all other categories, the Franklin Armory F17 L rated a 12 on a scale of 1 to 10.
Yet to be convinced that the performance of the rifle was typical of all Franklin Armory rifles in .17 WSM, I returned it along with an accuracy report and a request for replacement. Instead, the same rifle with a new barrel was returned to me along with a note indicating that the nut of the original barrel was not as tight as it should have been. Flyers that had originally plagued the rifle had been "exorcised." An occasional one did pop up, but it was much closer to its four mates than before.
Only five malfunctions were experienced during the three test sessions, and two were my fault. Failure to rap the back of the loaded magazine to make sure all cartridges were shoved to the rear caused a couple of failures to feed. At about the 400-round point, the magazine follower began to bind, but a few drops of FP-10 took care of that. Prior to shooting the rifle, I had applied the same lube to the exterior of the carrier and to the body and locking lugs of the bolt.
To answer a question on the minds of no small number of AR-15 owners, yes, the upper alone is available. Also included in the conversion kit are the necessary .17 WSM-specific magazine and buffer. When heading to the test range with the Franklin Armory F17 L, I also took along two AR-15s in .223, one built years ago by Eagle Arms, another from Les Baer. Switching uppers, buffers, and magazines was only a bit more difficult than falling off the proverbial log. On the first gun everything worked without a single hitch. When switching the upper to the second gun, I absentmindedly forgot to switch buffers. I did not shoot it that way, but when the carrier was manually retracted it hung up in the receiver. Retracting both the takedown pin and the pivot pin and separating the upper from lower took care of the problem.
Designing an AR to shoot the .17 WSM wasn't an easy task, but Franklin Armory with the F17 seems to have accomplished it. Some kinks had to be worked out along the way, but in the form of the Franklin Armory F17 L, the result is a nicely built rifle.