Make that Converted MAS 1949-56 Work Right

Many shooters bought one of the converted MAS 1949-56 rifles, thinking it would be a great truck gun or poor-man’s M1A. Then came the frustration when it didn’t work right; extraction problems, feed problems; it seemed that the thing was apiece of junk. How, then, did this basic design serve for more than 30 years, soldier ing in some of the most inhospitable places on the planet with utter reliability?

Yes, this rifle dates from work done well before France was occupied in WWII, resulting in the MAS 1944, then the MAS 1949, and culminating in the MAS 1949-56. The question is easy to answer. You see, if you have a MAS 1949 or 49-56 in its original 7.5x54mm MAS caliber, the rifle is dependable in any environment, any weather, anywhere, anytime. While some may sneer at the French Army of the 1950s, few will publicly ridicule the French Foreign Legion of the period, and they loved the MAS 1949 and 49- 56.

These rifles remained in French Foreign Legion service in one place or another until sometime around 1980. On the other hand, if you have one of those that’s been converted to 7.62x X51 NATO (.308), unfortunately, some important items got left out, ignored, or forgotten, and some critical corners were cut. None of these problems are insurmountable, but I would caution that this is advanced shop work that should be performed by a knowledgeable gunsmith. So What’s Different?

The 7.5 MAS looks vaguely similar to the 7.62x X51 NATO. Its performance is close to the 7.62×51 NATO cartridge. Well, in this case, close isn’t close enough! Problem #1 can occur without anyone noticing that it is a contributor to the rifle’s troubles. Many of these converted rifles’ chambers are too small. The rifle used in this article had a chamber so small that the bolt would not even begin to close on a "GO" gauge. Problem #2 is caused by higher operating pressures, changing the bolt assembly’s timing.

Military 7.5x54mm MAS ammo is a 139-grain flat-based spitzer with a muzzle velocity of around 2,600 fps. Average operating pressure is in the 45,000 psi range. NATO-spec M80 ball has a maximum average operating pressure of 62,000 psi, pushing a 147-grain boat-tailed spitzer at a specified 2,750 fps. Problem #3 reared its ugly head when they removed and shortened the barrel so they could ream its chamber to the stubbier 7.62 NATO.

Instead of simply setting the barrel back a couple of turns, it appears that they removed the entire shank and cut/ threaded anew one. This moved the gas tap closer to the chamber by about 1 inch, raising both the pressure and volume of gas available. Problem #4 is related to #1 and #3. Many of these converted rifles leak so much gas around the gas-tap block and from the socket in the gas-tap block where the gas tube fits that they don’t have enough gas to operate.

This is the usual culprit if the rifle is having "short-cycle" problems; in other words, partial extraction of the spent case with no ejection and no fresh round stripped from the magazine. The subject rifle in this article was leaking so badly that it wouldn’t cycle at all until I had fired about 20 rounds, which heated up and expanded the On the left is a 7.5x54mm MAS; on the right is a 7.62x51mm NATO.

barrel enough to seal the gas port. The pin holding the gas-tap block in place was so loose that it fell out when I removed the handguards. To make matters worse, the gas-tap block was loose on the barrel, and the end of the gas tube looked like it had been cut off and refitted using a hatchet. Problem #5 is caused by a difference in mechanical dimensions. The 7.5 MAS cartridge’s case head and extractor rim are 0.012 to 0.013 inch larger in diameter than the 7.62 NATO.

The unmodified MAS extractor will not hold a 7.62 NATO case under tension against the bolt face. This is the most likely culprit in those jams where the case is partially extracted with the rim undamaged (or slightly damaged), and the next round in the magazine is jammed up against the spent case. The extractor has lost control of the spent case. This is something the ignorant among us calla "double feed." That’s not the proper terminology, as the round in the chamber is spent. This is a failure to extract.

If the case is withdrawn from the chamber completely but becomes trapped between the bolt/bolt carrier and the receiver or barrel, it’s a failure to eject. By definition, a "double feed" would require two live cartridges to be presented simultaneously for chambering—and that’s a magazine problem. Words have meanings, folks; we must use specific and accurate descriptions to communicate technical information correctly. Dissimilar physical dimensions also cause problem #6.

There is enough difference between the two cartridges in body taper and case diameter at the shoulder that the unmodified 7.5 MAS magazine will not work well (if at all) with 7.62 NATO cartridges. First, it does not present the 7.62 cases (with their smaller head and rim) high enough to be picked up reliably by the bolt. Second, its feed lips don’t release the 7.62 cases early enough to push straight into the chamber, causing "bolt-over" jams.

Third, the 7.62 NATO is fatter at the shoulder than the 7.5 MAS; the magazine’s front guide lips push the 7.62 over too far and jam the bullet or cartridge shoulder against the barrel or receiver on the side opposite the round. To sum up these problems: The converted rifles are plagued with extraction, ejection, and feeding woes. If a semi-automatic rifle has any one of these troubles, it’s usually not around long. And one that possesses all these properties often becomes a trotline weight.

Check That Headspace To deal with problem #1, field-strip the rifle and clean the chamber and bolt/bolt carrier thoroughly. Leave them dry. Remove the extractor from the bolt by reaching into the opening behind the extractor’s flange with a small screwdriver and popping the spring out of the recess. Then push the face of the extractor back and away from the bolt. The extractor is MAS Barrel Replacement A perfectly suitable replacement can be made from an ‘03-A3 barrel, but this is not a job for the hobbyist.

The replacement won’t have the grenade-launcher ranging rings, of course, but then not many of us can run around blasting stuff with rifle grenades. The photo shows such a barrel. This is a brand-spanking-new two-groove ‘03 barrel that has been cut off at a point where its external dimensions are very near the MAS barrel, and anew shank has been turned and threaded.

What remains is to turn the barrel’s OD in the proper places to allow installation of the gasretained by an angled foot that engages an opening in the bolt body. Replace the bolt and bolt carrier in the rifle, leaving the firing pin and action spring out. Slide a "go-gauge" into the chamber and see that the bolt closes completely with no force required to seat the locking shoulder. Never use force trying to close any bolt on a headspace gauge!

If the chamber is too small (as was the case with the rifle used in this article) you’ll need to buy, borrow, or steal a .308 finish reamer (okay, okay, don’t steal one) and carefully open the chamber until the bolt will close on the go-gauge with the tiniest hint of "feel." If the chamber clears the "go," remove the gauge and try again with a "no-go." If the bolt closes on the "no-go," don’t have a cow—many military rifles have generous chambers.

Try again with a .308 "field" tap block and front sight, thread the muzzle for the muzzle brake (if desired – no, it’s not a flash suppressor; one round of M80 ball after dark will convince you), torque the barrel, cut slots for the front sight and gas-tap block locating pins, drill the gas port, and finish-ream the chamber. This barrel came with the rifle. I may finish it some day, but since the bore has cleaned up nicely, I see little reason to spend time on a replacement right now.

Who knows, however; I might need it if I come across another one of these "jewels in the rough" that I can tinker up for myself.

5 mag to 7.62. File deliberately and smoothly, taking care to remove the same amount of metal from both sides. Note the shape of the feed lips—very important for the magazine to work properly. When finished and the magazine works properly, be sure to stamp ".308" on the floor plate. 5 magazine. When you get one working 100 percent, measure every nuance of the feed lips to use as a guide for correcting other mags. gauge.

If it won’t close on the field gauge, it’s okay; the chamber is a bit long, but you’re not in danger of head separations with military brass or ammo loaded in military brass. I don’t recommend using commercial ammunition or reloads using commercial brass in any rifle whose bolt can be closed on a no-go-gauge.

If the bolt closes on the field gauge, it’s time to set the barrel back a turn or find another barrel. (See the sidebar on page 17.) Next, Fix the Magazine Let’s work the rest of these problems in reverse order, mainly because if the rifle won’t feed from the magazine, it’s very hard to diagnose any other problems it may have. Modifying the 7.5 MAS magazine to function with 7.62 NATO is very easy. You remove the base plate, pull out the follower and spring, and find your 10-inch smooth or second-cut file.

Open the magazine’s feed lips by filing and shaping as shown in the photo. Take care to remove equal amounts from each side. For example, take five strokes on one side, then five on the other. When the distances between the lips (measured as shown in the photo) are 0.500 inch at the front of the magazine and 0.650 inch between the rear lips, clean out the mag body and reassemble. Using some dummy 7.62 NATO FMJ ammo, load 10 rounds in the magazine and operate the bolt rapidly—just as the rifle does in operation.

If you experience malfunctions in feeding, work the bolt more slowly to try to identify the source of the problem. You may need to open the lips farther on one or both sides.

Failure to pick up around means the rear lip on that side needs to be opened a bit so that the cartridge presents more of its rim to the bolt. "Bolt-over jams," where the rifle jams with the point of the bullet in or near the chamber but with the case under the bolt (usually bending or denting the case) result when the case is not released early enough. Shorten the offending side’s rear lip where it arcs down toward the middle of the magazine, allowing the cartridge to clear the magazine sooner.

Other feeding jams, where bullets are shoved into the case because they are missing the chamber opening and running into the end of the barrel, are caused by the front feed lip on the cartridge side. It is too large and is "over-steering" the cartridge case. Open the front lip on the offending side until it "steers" the case’s shoulder to point the bullet at the chamber.

When the magazine is operating properly, disassemble it and sand or stone the filed areas to remove sharp edges and burrs that will scratch up your brass (and cause case failures for those that reload). Clean it all, lube lightly, and reassemble. Bolt and Extractor Modification Now we need to get the extractor grabbing the smaller rim of the 7.62 NATO round with a bit of tension. The extractor spring has a large coil on the inside end, which holds it somewhat captive.

Use ascribe or dental pick to pull the spring out. Clean the extractor, spring, spring pocket, and the recess in the bolt thoroughly. Remove about 0.010 inch from the bottom of the extractor foot as shown in the photo, and break the sharp edge on the front. Now get out your miniature diamond files, because the bolt is usually too hard for a regular file to cut. You want to remove about another 0.010 inch from the angled slot in the bolt where the extractor goes, and break the sharp edge on the inside.

Replace the extractor in the bolt (without the spring). Put a 7.62 cartridge in place against the bolt face, and hold the extractor in with your thumb. If you can hold the cartridge

in the bolt while shaking it gently, you’re ready to go. If the round falls out, you need to go back and remove a bit more from each surface until the extractor is "let in" enough to get a firm grip on the case rim. If you want a bit more insurance concerning extractor operation, you have a couple of ready options: replace the extractor spring with one of similar strength but just a bit longer, or make a small plunger to increase existing extractor-spring tension (my choice).

Now reassemble the extractor and spring into the bolt by inserting the foot and using a small screwdriver to compress the spring until you can tuck it down into the recess. If you made a plunger, getting the affair stuck together can be a little more difficult. Try making a cup-ended punch using a diamond or carbide ball with your high-speed rotary tool. Use the cupped punch to control the plunger and compress the extractor spring.

When completed, the extractor should hold a loaded round against the bolt with sufficient tension to keep it in place regardless of angle or position. Ideally, you should be able to shake the bolt around some before the cartridge works its way out. Now, About that Pressure Thing Altering the gas metering to the bolt carrier can be done several ways. What we want to do is soften and delay the initial gas-impulse moment’s amplitude and/or restrict the available gas volume.

Either of these will result in delaying the bolt carrier’s initial movement and slowing the entire cycle time. This gives our rifle time to allow barrel pressure to drop before unlocking the bolt and reduces the battering inflicted due to excessive pressure and the resultant higher action-cycle speeds. There are three basic approaches to this: (1) Bleed excess gas away, reducing the amount available to function the action similar to the FN49 and FAL/L1A1.

Note that bleeding gas off to slow the action cycle will only aggravate your problem if gas loss is the culprit in the rifle’s function problems. (2) Restrict gas availability with an orifice or valve, similar to many shotgun gas systems. (3) Increase the volume that the gas must fill before pressure rises high enough to begin moving the bolt carrier.

Of these, bleeding excess gas off is easiest to accomplish and it has an added benefit: The additional gas loss results in slightly lower bullet velocities, making it more probable that the rifle’s sight settings will more closely match projectile trajectories.

Remember, the 7.5 MAS cartridge has a lower muzzle velocity than the 7.62 NATO, and the rifle’s rear sight is calibrated for the The second option has the advantage of being either easy or allowing great flexibility in ammo selection by being adjustable, depending on which method you choose. The third option, increasing gas system volume, is the one I selected for this rifle, since they butchered the original gas tube’s front end during conversion so much as to be nearly useless.

This is much easier than it sounds, as you are simply replacing most of the gas tube with one of a larger internal diameter. The new gas tube will also provide the opportunity to fit the front end of the tube tightly into the socket, reducing or eliminating gas loss. This option has proved very successful for me, and is my first choice for solving gas-system-related problems. It seems to be relatively in sensitive to ammo fluctuations, temperature, bullet weight—you name it.

It is also an "invisible" modification, as the replacement gas tube is the same size as the original. In addition, the subject rifle shoots very near point of aim without having to adjust the front sight’s height. Note: While working on the gas system, leave the handguards off the rifle. To test, you can simply insert the lower guard in place and shoot.

This will prevent accidental damage to the upper guard where it is thinnest (under the band) and eliminate any possible damage to the band, such as accidentally "springing" it. The procedure for these three options are detailed Remove the handguards and observe the gas tube. Its offset is similar to the AR-15/ M16 genre of rifles. We’re going to want to get to the bottom—the side of the tube that faces the barrel. Drive out the gas-tube retaining pin and work the gas tube free.

Remove the tube and clamp it in your mill or drill press vise with the bottom side up. Drill a #60 hole in the bottom side about 1 inch from the end that goes into the gas-tap block. (We’ll call this the "front" end, to establish a short and easy reference point.) Don’t drill through both sides of the tube, and don’t drill the hole in the side of the tube that faces the upper

hand guard! Reassemble the rifle and test with at least 30 rounds. Should you have the same function problems, drill the hole one increment larger and retest. When the rifle is working properly, you’re where you need to be. Shoot it with a variety of ammo to be sure. (2) Metering gas flow into or through the tube. There are many ways to accomplish this, some easier than others.

Here’s what I came up with that was practical and didn’t cost more than the rifle is worth. "Method A," the quickest and easiest way I can think of, is to insert a steel plug in the front end of the gas tube and drill an orifice in it (see Figure A). Cut just a bit less than 1/2 inch from the front of the gas tube. Carefully open the end of the tube to 0.180-inch diameter (#15 drill) and about 0.250-inch-plus deep. Fabricate the steel plug detailed in Figure A and sweat it in place with silversolder.

Replace the tube, bolt and bolt carrier, action spring, and receiver cover. Now, fit the tube for overall length by placing a BB or some similar spacer in the bolt carrier’s gas-tube hole, and use the action spring and bolt carrier to press the tube extension ("spigot," for lack of a better term) forward. Observe the gap between the tube-support boss and the shoulder on the tube. Dress this amount from the new end of the tube and retest.

Your goal is to have the tube held tightly against the bottom of the socket in the gastap block and the spigot’s shoulder against the corresponding boss. The spacer is necessary because we don’t want the bolt carrier hammering the end of the spigot; there’s a bit of clearance between the spigot’s end and the bottom of the blind hole in the bolt carrier. Figure A.

Make sure the tube is parallel with the barrel, secure the tube to prevent it from rolling (I use a liberal application of duct tape), and carefully redrill the retaining-pin hole. Install the tube-retainer pin and remove the spacer from the bolt carrier. Try the rifle with 20 or so rounds. Work orifice size up in the smallest increments available until the rifle operates properly. When the rifle eats everything it’s offered, you should be finished.

This will get the rifle working properly, but it may still have an occasional problem with ammunition other than what it was calibrated to use. "Method B" calls for replacing the grenade launcher shutoff with an adjustable valve. Basically, you replace the all-or-nothing shutoff with a needle valve made from a machine screw, thereby allowing you to vary the amount of gas allowed into the gas tube. This method will alter the rifle’s external appearance.

It may or may not be an issue since these rifles are almost as butt-ugly as British military handguns. To do this, we need to take the gas-tap block off the rifle. Remove the compensator, locking washer, and jam nut from the muzzle. Also remove the grenade-launcher collar, if present. Drive out the front-sight base’s retaining pin and work the front sight off the barrel. Drive the gas-tube retaining pin out, and work the tube free of the gas-tap block.

Now drive the gas-tap block retaining pin out and remove the tap block. Encouraging the tap block with a plastic or leather mallet may be necessary. At this point, you can easily see how the gas shutoff works. Remove the retaining clip from the semicircular side, and push the shutoff out toward the side with the screwdriver slot. Take care to contain the shutoff handle, the detent, and its spring. Put the shutoff components in a bag or box for spares or for future use.

Next, you’ll fabricate a steel plug to replace the shutoff. It needs to be a light press fit in the hole, and its ends should be flush with the sides of the gas-tap block. Using a #25 drill, bore up through the hole in the bottom of the gas-tap block. You want this hole to go through the plug and out the top of the gas-tap block. It should exit at or very near the dimple for the shutoff detent.

Now insert a suitably-sized filler through this hole (brazing rod or toothpick, etc.) and drill the same #25 hole perpendicularly into the plug through the gas-tube socket until the drill enters the other hole. You’ll know this happens when whatever you used as filler comes out with the drill shavings. Clear the holes of filler material and make sure the side gas-tube hole is full-diameter into the vertical hole.

Now drill from the top of the gas-tap block down even with the bottom of the gas-tube hole (the perpendicular hole) with a #28 drill and tap #8-40 completely to the bottom. Chuck a filister-head #8-40 x 1/2-inch machine screw in a lathe or drill and cone-point the end. The angle is relatively unimportant. A blunt end does not offer extremely

Figure B. fine adjustment; on the other hand, a very fine-pointed end is more prone to erosion from routine "sandblasting" with burning powder granules. Install the screw, reassemble the rifle, test, and adjust until the rifle operates properly. To prevent unintentional screw movement, put a stout spring between the screw head and the gas-tap block or use a bit of the wicking-type thread-locking compound.

You may also want to adjust the screw’s slot so it can be turned with the rim of a cartridge case. (3) Increase gas system volume, changing the pressure curve to the bolt carrier. As stated before, I used this method because the subject rifle’s gas tube was just about useless. This is a logical variation of the "pigtail" replacement gas tubes for shorty ARtype rifles that basically accomplish the same thing—the extra length of gas tube means an increase in gas-system volume.

This extra volume serves as a "shock absorber" to delay the pressure rise and modify the impulse applied to the bolt carrier. Since there’s not room enough under the MAS handguard for one of these curlicue tubes, we’ll have to change the gas tube’s internal diameter to increase its volume. The MAS gas tube is about 0.250 inch OD and 0.150 inch ID. The AR- 15/M16 gas tube is 0.180 OD and 0.150 ID. It makes a perfect coupling for the new gas tube to be installed.

You’ll need 12 inches of 1/4-inch OD steel tubing with a 0.035-inch wall. (I used stainless tube; it was what I could find.) This gives you a 0.180-inch ID tube. Your final gas-tube assembly will utilize about 8-1/2 inches of this larger-ID tubing, effectively increasing the gas-tube volume around 44 percent. It’s hard to believe that this 0.030-inch increase in ID would change its volume by that much, but remember that a circle’s area increases by the square of its radius.

Therefore, a cylinder’s volume changes in a linear relationship with its length, but geometrically with a change in its diameter. See? Not all that highschool math they tried to pump into your head was useless. See Figure B. Remove the gas tube from the rifle. Cut the gas tube off 1.25 inches from the end of the spigot. Bore the hole through the spigot to 0.180 inch (#15 drill), and bevel the hole on the big end with a 60-degree countersink. Note: The Figure C. large part of the spigot is very hard.

You may want to anneal the spigot, drill and countersink, then reharden the end. If you do, be sure to draw the hardened spigot some to prevent its shattering under stress. You could also make anew spigot from drill rod and surface-harden the end. I’ve done it both ways, and don’t have any real preference for one method over the other.

Next, cut a 2-inch piece from an old AR-15 gas tube and chamfer the ends inside and out. (This piece needs to come from the long straight part of the tube, between the gas orifice and the offset. The front is plugged, and the short rear part that goes into the upper receiver is smaller in diameter with a "bulb" on the end.) Push the tube through the spigot so that about 1/8 inch is protruding from the large end.

Fill the small tube with apiece of music wire or a twist drill to prevent crushing, and clamp the small tube in a smooth-jawed vise with the small end of the spigot against the vise. Use a center punch to flare the end of the small tube to approximately match the countersunk area of the spigot. Remove the assembly from the vise, remove the filler from the small