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Browning Automatic Rifle
Courtesy, American Gunsmith Magazine

To free up a stuck gas piston, you need a device called a slide hammer. They’re not commercially available, but you can fabricate one from a scrap piece of .30-caliber barrel, a steel rod, or a short length of iron pipe.

The Browning Automatic Rifle


September 13, 2012

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Browning Automatic Rifle, John M. Browning, Naval Ordnance, Gatling gun, The Browning Automatic Rifle

Accepted by the military in 1917, the civilian version of the BAR has become a popular, reliable sporting rifle.

Chick Blood

When John M. Browning demonstrated his first machine gun—a .45/70 caliber prototype—it smoked up the Colt factory’s firing tunnels by letting loose 200 rounds at six rounds per second without a hitch. Naval Ordnance was somewhat interested, having talked over the need for a lightweight gun that could serve with landing parties as a replacement for the 90-pound Gatling gun. With no war in sight, the Army wasn’t interested at all. The year was 1891.

Little more than a month before the United States entered the war against Germany in 1917, Browning officially demonstrated his two newest brainchildren for an audience of senators, representatives, military officers, and assorted members of the press. One entry was a .30 caliber, water-cooled machine gun capable of discharging 600 rounds per minute. The other was a rifle light enough to be carried by a foot soldier, fired from the shoulder or hip and instantly convertible from single shot to fully automatic fire at 480 rounds per minute. The Browning Automatic Rifle (BAR) was an immediate hit. It wasn’t until World War I hit home in April that Browning’s machine gun joined it.

While both designs—or refinements thereof—are still in service with the U.S. Military, the BAR made a successful transition to the sporting firearms market. Its civilian dress differs considerably from its GI garb, and, of course, the civilian model is not capable of fully automatic fire. Outside of that, it’s much the same rifle Browning brought to Washington in 1917.

There are old and new styles of the BAR. The new style has a flat receiver with both sides parallel. The old style’s receiver is flared, with its rear end thicker than its center. Old and new style receivers are not interchangeable, nor are the butt stocks, stock bolts, stock butt plates, triggers, or front and rear sights. As a complete assembly, however, trigger guards are interchangeable.

The magazine capacity of the BAR is four rounds regular, three rounds magnum. The rifles are equipped with a cross-bolt safety to block trigger movement when the safety is on. When the trigger is pulled with the safety off, it rotates around the trigger pin, allowing the disconnector to move forward and disengage the sear from the hammer. The hammer, driven by two springs, strikes the firing pin. The firing pin moves forward, compresses the firing-pin spring, then strikes and ignites the primer of the cartridge.

As the bullet moves down the barrel, it passes a port where propellant gas is bled off to drive the gas piston to the rear. Any excess gas is bled off through the gas regulator. The gas piston travels about 5/8 inch before contacting the inertia piece, which is connected to the bolt sleeve by action rods. Picking up the momentum of the inertia piece, the bolt sleeve is driven rearward. This begins to compress the action spring. At the same time, the cam pin rotates the bolt, unlocking its lugs from those in the barrel. During the process, the timing latch engages a slot in the left side of the receiver. Once the bolt is completely unlocked, the timing latch cams into the bolt sleeve to keep bolt and barrel lugs aligned until the bolt is returned forward. Extraction and ejection take place as the bolt is on the way to the rear. In addition, the tail of the bolt sleeve depresses the hammer past the cocked position to disengage the sear and the disconnector and compress the mainsprings.

All this activity is halted when the action’s rearward movement is stopped by the inertia piece striking the buffer and buffer plates, which are located in the front end of the receiver. By this time, the action spring has been fully compressed and reacts by starting to move everything forward. The bolt then gathers the next round from the magazine, starts it toward the chamber, and raises the hammer into engagement with the sear. Since the disconnector can’t reengage the sear until the trigger has been completely released, the rifle cannot be fired full auto. Another mechanical feature preventing this is the tail of the bolt slide, which keeps the hammer out of contact with the firing pin until the bolt is locked. This occurs when the timing latch has been cammed into its receiver slot, the cam pin has rotated the bolt into the barrel’s locking lugs, the extractor has grabbed the rim of the just-chambered round, and the inertia piece has returned the gas piston to its unfired forward position.

To avoid taking up space with information easily found elsewhere, we’ll skip the details of stripping down a BAR, and simply refer you to Gun Digest’s Book of Assembly/Disassembly for centerfire rifles.

Dirt: The BAR’s Worst Enemy

As for causes and cures of malfunctions—which you won’t easily find elsewhere—start with dirt. Dirt can be formally defined as accumulated residue which has been transformed into a sticky amalgam by a lubricant base. More simply put, dirt is the BAR’s worst enemy. Especially in cold weather. Scrub it loose; flush it away; don’t over-lube a cleaned-up gun; and be careful of the lubrication used. Some brands dry out or build up and only make matters worse sooner. If you even suspect the lube on your bench could be among them, use Browning gun oil—sparingly—on the extractor spring, bolt, inside the bolt sleeve, on the bolt sleeve rails, as well as on the action spring and exterior surfaces.

But that’s not all the dirt about dirt. Dirt can make the safety difficult to operate when it builds up between the trigger and trigger guard. By building up between the sear and trigger guard, dirt can prevent the hammer from cocking. It can cause failures to fire when it collects between the trigger and trigger guard. Dirt can cause failures to eject by binding the ejector in its hole, clogging the barrel’s gas port or gunking up the gas piston and short cycling when it fouls both the piston and the gas cylinder. At its worst, dirt can “freeze” the piston, which can require considerable bashing to liberate. This bashing is not to be accomplished with punch and sledge, but with a device called a slide hammer. Since it is not commercially available, you must make one yourself—ideally, from a scrap piece of .30-caliber barrel. Lacking a barrel, you can fabricate a slide hammer from

Browning Automatic Rifle
Courtesy, American Gunsmith Magazine

An oversize gas regulator orifice can cause ejection failures. The table lists the gas-regulator orifice maximums, minimums, and nominal dimensions (first set of three numbers). As you’ll note, there’s a different specification for almost every caliber. The size of the barrel’s gas orifice is also critical to proper functioning of the gun. As the table shows (second set of three dimensions), the difference between the minimum and maximum is very small. An oversized orifice can be restored by plugging and resizing, but the operation calls for precise tooling.

a steel rod or a short length of iron pipe to the dimensions shown in the accompanying diagram. Barrel, rod, or pipe, the finished tool is slipped around the action-spring guide. The inertia piece is then retracted and allowed to fly forward as many times as necessary to free up the gas piston.

Other Potential Problems

From here on, we’ll assume that dirt isn’t causing the problem you’re facing, and we’ll examine other possibilities. We’ll assume the rifle is clean, nicely lubricated, but still fails to eject. Is the ejector damaged or missing? Is the ejector spring damaged or weak? Is there interference (rubbing) between the action rods and the forearm?

Damaged, missing, or weakened parts should be replaced. Interference is eliminated by carefully scraping the interior surfaces of the forearm and/or deburring the action rods.

This may come as a surprise: If the rifle has been scoped with Weaver-style mounts, a failure to eject can result from the mounts interfering with ejection. It’s not their fault. They’ve been installed wrong. On the BAR, the ring clamp must be to the left side. Then again, the scope-base screws may be too long and, as a result, are rubbing the bolt sleeve. Another culprit could be the sling eyelet. If it’s too long, it could be getting in the way of the gas piston.

All those problems are easy to set straight. Ejection failures due to an oversize gas-regulator orifice are another matter. As you can see from the accompanying table, there’s a different gas regulator for almost every caliber. Check the orifice size of the one in the rifle and see if it matches up with its caliber. Why anyone would drill out or switch a gas regulator to make the gun “work better” is a mystery, but it happens. There’s no way to restore an oversize regulator. It has to be replaced with one that meets specifications. But there’s an exception to that rule: If the orifice in the regulator is merely clogged, you can clean it out as long as you’re careful not to enlarge it. Clogged regulators don’t effect ejection, but do cause failures to feed because the action cycles too rapidly.

Most feeding problems, however, are traceable to the magazine. Its lips may be rough or bent. Its spring may be broken. Its follower may be binding. Smoothing up and/or replacement cure them all.

Another reason a BAR refuses to ingest a cartridge is a sharp edge at the chamber’s rim. As long as you’re careful not to invade the chamber, you can break that edge with a stone. Besides that, the bolt cover may be too tight or too loose. If so, here’s how to adjust it: To tighten the fit, lightly strike the side of the bolt cover with a nylon or brass hammer; to loosen the fit, strike the top of the bolt cover.

So far, pretty simple. It’s when an enlarged barrel gas port causes failures to feed that things get more complicated. Like the gas regulator, the size of the barrel’s orifice is speced according to caliber, and allows just enough propellant gas to be bled off for proper function. The charts show how critically small the difference between minimum and maximum serviceability is. To restore an oversize port to its factory dimensions, you must plug and resize it. According to Browning’s field service manual, this is accomplished by perpendicularly drilling for a 6-48 screw through the stud hole of the gas cylinder, 1/4 inch into its base. The stud hole serves as your drill guide; avoid drilling into the bore of the barrel.

Tap the hole just drilled and file a slot into a 5/16-inch length of 6-48 screw stock. (You can use a one-inch cap screw to make this by cutting off its head.) Apply LocTite and tighten the screw in the hole. With a #21 bit and the stud hole serving again as your guide, drill away the protruding portion of the plug screw. Make sure the bit goes a little deeper than the screw’s slot to give you a center point for your next drilling operation. Now select a bit that exactly matches the specified diameter of the barrel port, and drill through the middle of the plug screw into the bore. Polish the inside of the gas cylinder to clear away any burrs. It’s a good idea to scrub the bore itself with a stiff bronze brush or mildly lap it.

These drilling and tapping operations call for tooling that stays put once it has been set up. Handheld drills and taps are too risky. If that’s all you own, either find someone who will let you use an industrial-quality drill press, or send the rifle back to the factory.

Once a round is chambered, failures to fire can be attributed to the bolt’s not closing completely. A sticky gas piston is one cause. A too-tight bolt cover is another. A burred timing latch is a third. A bolt that closes completely, but with some difficulty, does so because: (1) the action rods and forearm are interfering with each other; (2) the action rods or support rails are binding in the receiver; or (3) the bolt sleeve is cracked. We’ve already covered action rods and forearms. And all you can do with a cracked bolt sleeve is replace it. You may be able to clear up rod and rail binding by closely inspecting all interfacing surfaces for burrs or dents and smoothing them up. Serious damage to the receiver usually requires Browning’s attention.

A hammer that fails to cock has nothing to do with the bolt’s not closing—and everything to do with the rifle not firing. If the problem isn’t dirt that has lodged between the sear and trigger guard, there are two other reasons a hammer does such things: The last coil of the lower end of the disconnector spring could be binding its plunger in its hole in the sear, or the trigger-guard assembly contains broken parts. To correct the binding, spread the disconnector spring’s last coil. The only thing you can do about broken parts is order in new ones.

If you’re interested in delving still deeper into the BAR, give Browning a call and ask them to send you a field-service manual. .

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