February 6, 2014

Working the Browning A-Bolt

GunReports.com finds that it’s relatively easy to spot trouble in a simple bolt-action design, and the Browning A-Bolt is about as simple as they come. Adapted from American Gunsmith book series, Gunsmithing the Rifle.

After it grew up from a nice .22-caliber plinker with a fast bolt, detachable magazine, and top-of-the-tang thumb safety, the A-Bolt found great popularity as a centerfire game getter for all the same reasons. Still produced in .22 and .22 Magnum, the rifle is available in 11 other models and 16 heavier calibers. In its newest incarnation, the A-Bolt’s bolt has been further slicked up with a non-rotating sleeve running its entire length. This feature reportedly assures more precise alignment in the receiver to prevent binding.

I scanned a slew of books, including DBI’s series on disassembly/assembly, searching for detailed take-down instructions for the big-bore A-Bolt. I found none. Since I didn’t, I’ll include them here, right after walking you through a pre-disassembly inspection—which should be undertaken in the exact order given:

1 With the action cocked, move the safety to the On position, and pull the trigger hard. Use both index fingers. The firing pin should not fall.

2 Next, open the action. When the bolt handle is raised, the firing pin should not fall.

3 Close the action completely and, with the safety in the Off position, partially disengage the sear by lightly pulling the trigger.

4 Release the trigger slowly. You should be able to feel the trigger/sear interfacing surfaces fully reengage.

After that, check the trigger pull with a set of weights. I’ll get into the minimum and maximum allowable let-off factors later on.

Disassembly and Inspection

Basic field stripping begins by removing the barrel mounting screw and the trigger guard screw. Open the bolt fully to the rear, grab it in one hand and the forearm in the other. While applying upward pressure on the bolt, strike the barrel downward on a well-padded bench surface to free the action from the stock. To separate the bolt from the receiver, depress the forward end of the bolt retainer and remove the bolt to the rear.

Bolt Body. With the bolt assembly cocked, secure the rear of the firing pin sear in a vise with padded jaws. Pull the bolt body toward you to compress the firing pin spring, then unscrew the body from the bolt shroud. After one turn, you can let up with your pulling because the assembly will unscrew easily. Next to come out is the firing pin assembly, which includes the bolt shroud. And watch out: It will come flying out hard enough to hurt you if you don’t keep it under control.

The bolt handle pin is drifted out through the bolt body with a 3/32-inch punch. To separate the bolt body from the handle, suspend the handle across your vise jaws with the body hanging down. Don’t clamp the body in the vise. Insert an old firing pin or similar diameter pin into the bolt body. Use a nylon or leather mallet to gently drive it downward and free the bolt handle. Check the bolt body for cracks, especially in the milled grooves. If cracks are present, replace the bolt body. If burrs show up in the bolt body retaining slot, remove them with a fine-cut file. Such burrs can cause hard opening of the bolt.

Courtesy, American Gunsmith

Courtesy, American Gunsmith

Use a large brass punch to remove the bolt head key, bolt head assembly, and gas stop assembly. Remove the extractor spring from its groove around the neck of the bolt head, then remove the extractor. Clamp the neck of the bolt head in a padded vise and use a 1/16-inch punch to partially drift out the ejector pin. You’ll have to work from the side closest to the ejector for this. Withdraw the punch to remove the ejector and its spring. Keep both parts under control when you pull out the punch or they’ll both end up in some dark corner.

Look for cracks or broken-out areas in the bolt head, paying particular attention to the extractor slot. Deburr the extractor spring hole, if needed, with a #29 reamer or drill bit. If the camming surface of the bolt handle shows signs of roughness, polishing it will prevent, or correct, any contribution a rough surface makes to hard opening.

Finally, inspect the notch on the rear of the bolt handle for excessive wear or damage. It has to hold the nose of the firing pin sear when the handle is fully opened. If it’s not deep enough, or broken in one way or another, it can’t do its job.

Firing Pin Assembly. After gripping the lower edge of the firing pin in your vise, pull forward on the bolt shroud. Lift up on the shroud and tip it toward its rear to remove it. After drifting out the firing pin sear pin with a 1/8-inch punch, separate all the components for inspection.

First, check the firing pin for straightness. A bent firing pin will create excessive friction inside the bolt assembly and cause light hits on primers. Check the beveled edge of the firing pin washer for burrs. They can make the bolt hard to open. Clean up any you find with a cone-shaped stone chucked in a Dremel or “moto tool.” To prevent or correct for misfires, count the coils in the firing pin spring. Older model A- Bolt springs have 33 coils. Newer model springs have 36. If the spring has less than 36 coils, replace it.

Unfortunately, there are no detailed disassembly instructions for the trigger assembly. It’s a factory-only service item. But there are some very specific inspections you can make. Rotate the safety to the Off position and use a feeler gauge to see if the engagement between the sear and trigger is less than 0.030 of an inch. If it is, ship the assembly to Browning’s Service Center in Arnold, Missouri. Things could be worse. If the trigger moves before there’s contact between the safety stud and safety, the whole rifle is Missouri bound. To see whether or not that’s in your future, move the safety to On, magnify your view of the stud, and pull the trigger firmly.

Fortunately, adjusting the trigger pull is something you can handle. These adjustments are made with the trigger and bolt assemblies installed. Let-off on the A-Bolt is specified from 3.5 to 6.5 pounds. To increase the pull, turn the trigger pull adjusting screw counterclockwise. To lighten it, turn the screw clockwise, but never bring the pull down to less than 3.5 pounds. After adjustment, tighten the adjustment screw lock nut to maintain the setting.

Courtesy, American Gunsmith

Courtesy, American Gunsmith

Other Trouble Spots. If the bolt interferes with the magazine and won’t close, it’s not the bolt’s fault. The rear tab of the magazine may not be positioned under its retainer at the rear of the floor plate. Or, the stock or floor plate hinge may have been too deeply inletted, causing the bolt to drag on the magazine. Try placing thinly cut shims to correct for the excessive inletting. If that doesn’t work, you’ll have to build up the stock’s interior and re-relieve it. Mixing Brownells Acraglas with sawdust makes a good filler that routs, files, and scrapes nicely. Your other alternative is a new stock.

Rough or stubborn bolt operation can be caused by a bolt head key that is misaligned with the firing pin. Since this most often happens because the bolt body has been improperly reassembled, here’s the right way to install the bolt key: Start it in the bolt head and body by aligning the key longitudinally with the body. Positioning the forward end of the firing pin in the key aids in this alignment. Then remove the firing pin and drive the key flush with a rawhide mallet. Reinsert the firing pin to double check the alignment.

Another possibility for balky bolts is scope base screws. If they’re too long, they’ll hold a base secure no matter what, but they’ll drag like the dickens on the bolt surface.

Reassembly Tips

Make sure the milled edge of the extractor is positioned downward and is 180 degrees from the bolt retainer slot in the bolt body. The same number of degrees of separation should be observed with the bolt handle prior to installing the bolt handle pin.

Reuniting the bolt body and firing pin assemblies calls for some “high-technology” tooling. You’ll have to manufacture it. One method is to start with a scrap piece of hardwood. Oak is best. From it, cut a block 3/4 x 2 x 3 inches. In the exact center of one end, drill a 1/4-inch hole 2 inches deep. Seal and sand the entire piece to avoid splinters, and open the jaws of your vise a little bit wider than the firing pin sear is thick. Grasp the block securely in one hand and tighten the vise on the firing pin sear with the other. Insert the firing pin spring, capture its protruding end in the hole in the block and fully compress the spring while holding on to the block. Keep holding on, and screw the bolt body onto the firing pin assembly. Now set the block aside for possible future use and unscrew the body less than half a turn to line up the point of the firing pin sear with the bolt-open notch on the bolt handle. Loosen the vise and make sure the point of the firing pin sear drops into the notch.

Another tool-manufacturing technique has been developed for those who prefer metalworking over woodworking. Simply weld or solder a piece of brass tubing slightly larger than the firing pin spring to a brass rod. Whether or not you add a handle is entirely up to you. As long as you apply it in the same way as described for the wooden block, the result will be the same.