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The Mauser Project - Part 2

By Steve Ostrem

Before getting started I’d like to thank those of you who took the time to e-mail us with your comments and suggestions. It appears that I am not the only one with a Mauser project on his hands. In fact, according to the feedback received, at least half a dozen of you are building one in .257 Roberts also! A lot of people think that interest in sporterizing military weapons is almost non-existent these days with all of the commercial actions that can be purchased ready to go. Apparently they’ve never shot a Mauser or learned to appreciate the sheer excellence of the design. The fact is the Mauser action has proven itself to be the perfect vehicle for the custom rifle builder regardless if the finished product is destined to be made into an elegant and expensive custom rifle or screwed into a synthetic stock and thrown into the back of a pickup. So without further adieu, let’s get started.

The first order of business is to inspect the action to make sure it is safe to fire. Unlike modern rifles whose actions are machined from higher carbon steels and hardened uniformly throughout, the Mauser is basically soft inside and depends on design for its strength. They are made of mild steel with a very hard case-hardened skin. This extra hard skin reduces wear on the moving parts and increases the smoothness of operation. What this means to us is that there is the possibility of damage to the action in the lug recess area of the receiver, particularly if the action has been subjected to heavy handloads or previously converted to a cartridge with unsuitably high pressure. This can cause “set back” of the lugs in the receiver, and at the very least can cause hard opening of the bolt if a round is fired. This happens when the bolt lugs have to climb up an incline or over a step as they are rotated out of battery, causing the bolt to move forward against the fired case.

This area is fairly easy to check with a depth gauge, and a gunsmith can do it for you if you don’t have a way to measure this area. However, if the rifle still has the military issue barrel and allows easy bolt opening after firing, you probably don’t have anything to worry about. Still, it pays to inspect this area once the barrel is removed. The same applies to the bolt lugs. Check them for obvious damage and try a file across the back of them. They should cause the file to skip off without cutting. (No need to really bear down on the file; just normal pressure.)

This is where set-back can occur.

The goal here is to make absolutely sure the surface hardness remains in the critical areas. If you find the action is soft it will need to be re-heatreated or rejected for the project. A soft action can set back in one or two shots with a modern caliber and ruin all of your hard work up to that point. A good source for Mauser inspection and safety is Jerry Kuhnhausen’s Shop Manual (#924-400-098) on the Mauser rifles. In fact, every Mauser mechanic out there should have this book in his collection. I can’t recommend it highly enough, and refer to it often when doing a project like this.

Looking across the bottom will show if the receiver has been twisted or distorted. Ours looks good.

While we’re examining the action, be on the lookout for cracks or fissures anywhere on the metal. Sometimes damage is done by well-meaning, would-be gunsmiths when removing the old barrel or installing another without the proper equipment. This can stress the action unnecessarily. This applies more to Springfield and Enfield actions which are prone to crack in the thin spot on the right front side of the receiver, but even the mighty Mauser can be damaged with a long enough handle on a pipe wrench.

Also, take a good look at your action from the front and rear and check for any evidence of twisting or “warping” caused by torsion applied in an improper manner. Luckily, most of these fine old veterans have been sporterized by simply remodeling the stock, leaving the original barrel in place, and resulting in no permanent damage. These are the guns I like to find for my projects. You’ve all seen the at the guns shows, lying forlornly on the table with their butchered stocks, often at a good price. These can be the starting point for a great gun, so take a close look when you see one.

The first thing I like to do, assuming that rebarreling is in order, is to remove the barrel. For this you need three things: A barrel vise, an action wrench, and Kroil (#471-100-008). After many years of removing barrels and screws held in by decades of rust, I’ve become a big believer in using plenty of Kroil to free things up. Many of the surplus guns have been stored under less than ideal conditions and have suffered corrosion on the inside. Kroil can easily cut through this and make disassembly much easier. Once the barrel is off, the inspection of the receiver can be undertaken.


Receiver Facing Mandrel can be used in the lathe to true the front.

 

With the action inspected and found to be in safe condition, the front of the receiver can now be trued if desired. The Receiver Facing Mandrel (#080-098-001) allows the action to be set up in the lathe and a skim cut can be taken off the front. The receiver I have, like most of them, is already pretty true and I saw no need to do any cutting. On the other hand, had the front surface been corroded or damaged in any way, this would be the way to fix it. For those of you who do not have a lathe and are using a pre-fit barrel it is best to skip this step, as shortening the front of the receiver would necessitate removing the same amount from the end of the barrel shank as well. Without a lathe it would be a lot of work and the gun will probably shoot just as well if this step is skipped. If, on the other hand, the condition of the metal makes truing up the action necessary, you’ll need to find a gunsmith with a lathe to do this operation for you.

Now that the receiver is ready we can install the barrel. For many of us, the pre-fit barrel is a great way to build up a rifle, because it allows the job to be done with only hand tools. Brownells offers a very good variety of pre-threaded/short-chambered barrels for the large ring 98 Mauser and the small ring Mausers like the ’96 Swede and others. If you are unsure which Mauser you have please give us a call at 1-800-714-0015 and ask for Tech Support. We can usually figure out what you have pretty quickly if you have the gun in hand to examine for markings and other details.

Barrel vise and Receiver wrench for barrel work. The Kroil helps get those old, rusty barrels off.

If shopping for an action, bear in mind that the large ring 98 Mauser is preferred over the small ring version like the 93 through the 96 by most rifle builders because of their ability to handle the modern cartridges of higher pressure and greater length, like the .270 for instance, with relative ease. The small ring Mausers, lacking the third safety lug on the bolt, are better reserved for the milder chamberings like the 6.5x55 or 7x57 whose pressure falls into the 45,000 CUP area. The choice of calibers in the pre-fit barrels we offer for those guns reflects this need to stick within safe limits. Many of you have probably converted the 96 Swedes to high pressure calibers like 7-08 or 22-250, I’ve done it myself. These actions are of such good quality and workmanship that they seem to take the higher pressures in stride. Still, I cannot wholeheartedly recommend the practice, and only do it myself on a case by case basis. By the way, the Swede is a great platform for the 257 Roberts and I would have gladly made one had a good action been available. I want you to know that I have nothing against the small ring guns; they just have their limitations. The only one I don’t bother with is the ’91 Argentine with its protruding, single stack magazine and odd extractor. If you have one of these I would leave it in the original caliber, put in a nice stock, and make the necessary alterations for a scope and/or sights.


If you work on Mausers, this is the book to get.

Even with a pre-fit barrel there is plenty of work to do. If there is any difficulty screwing the barrel into the receiver it may be necessary to clean up the internal action threads. To do this Brownells has had a special receiver tap (#080-098-001) produced that makes this operation a snap. If you have a Turkish 98 action, be advised that this is a large ring action with small ring threads. We no longer carry pre-fit barrels for these guns, but we may be able to special order them from Shilen if you need one. Give us a call and let us know.

With the barrel screwed into the action we are ready to figure out how far the chamber needs to be lengthened. What I like to do is insert the Go gauge into the chamber and unscrew the barrel until the bolt will close. The gap between the receiver and the barrel shoulder then gives me a pretty fair idea of how far is left to go. Normally there will be a gap of .050” or so. Remember, the goal is to ream the chamber deeper until the bolt will close on the Go gauge but will not on the No Go gauge. To do this, put the barrel in a padded vise, put a tap handle on the chambering reamer, apply cutting oil, (I use Tap Magic, but any cutting oil will do) and insert the reamer into the chamber. The first time you do this it is hard to know just how hard to push on the reamer as it is being turned, but you’ll feel it cutting and quickly learn how much pressure is needed to make it cut well.

Reaming the barrel by hand.

After a couple of turns remove the reamer and examine the metal chips it has cut from the chamber. There should be chips mostly toward the front of the reamer in the shoulder area but also on the front of the neck and along the sides to a lesser extent. Clean the chips from the chamber and the reamer and turn the action onto the barrel with the Go gauge in place. Removing the extractor makes this easier.

The gap between the barrel shoulder and the receiver should have grown smaller, and will do so every time you make a cut. Soon the gap will be so small you’ll need to use a feeler gauge to measure to distance. When you get below .010”, (ten thousandths), you need to proceed with caution. When the barrel is screwed all the way in and you can close the bolt with no resistance, you are there. Now, put in the No Go gauge. The bolt should not close. If it does you’ll need to have the barrel set back a little bit on a lathe and try again. One little tip: while cutting the chamber, put the No Go gauge out of sight or away where you cannot reach it. This prevents you from grabbing the wrong gauge in the heat of battle and reaming too far. A little mistake like this is very easy to make. Please don’t ask me how I came to know about this. All I can say is that it can happen to anyone!


Headspace gauges will keep you out of trouble; just don’t mix them up!

If the Go gauge goes and the No Go gauge won’t, it’s time to go to the barrel vise and tighten that barrel up. Then, check again to make sure the bolt still closes easily on the Go gauge. If not, simply ream out a bit more; just a thousandth or two; no need to get carried away. Then reassemble and check until every thing is just right. Congratulations; you’ve got yourself a barreled action! Now let’s cut it to length and do the crown.

The length of the barrel is a personal matter. Short ones are handier and louder, long ones require more room to maneuver and are heavier, but give a longer sighting plane. Most sporting rifles seem to have barrels that fall into the 18” to 24” range. Once you decide on the length you want, measure the barrel and mark it where it needs to have the excess cut off. Then measure it two more times to make sure. Barrel shortening is a one-way street and you’ll have to live with any mistake you make at this point. Now that you a 100 percent sure of where the cut should be made, put the barrel in your vise and remove the unwanted length with a good hacksaw. Please don’t use the one you found in the garage with no teeth left on it. For this job we really need to splurge and buy a new blade. Otherwise it could take you all afternoon to get through that hunk of steel. Once you have it cut down to size, put the barrel vertically in the vise with the cut side up and use a file to smooth and even up the muzzle as best you can. This will make it easier to get a good crown with the hand tools we are going to use. Brownells has a complete system for crowning barrels by hand, and once you have the basic handle and necessary cutters, any caliber can be done by simply purchasing the correct pilot for the bore size. Check out a list of cutters and pilots. With these tools a professional crown job can be done on rifles or pistols with hand power alone. True, some people can produce an acceptable crown with a file and some practice, but I’ve never had much luck at getting the muzzle even enough to suit me. The Brownells muzzle crowning equipment lets the beginner get it right the first time, and is the only good way I know of to get the job done without a lathe.


Faced off at 90 degrees.


Cutting the 45 degree chamfer.

The trick to using the Brownells crowning tools is to go slowly with light but firm, even pressure. It is all too easy to get chatter with hand tools, so take it easy. If you get chatter while using the 90 degree tool you can file or grind the muzzle flat and try again. It’s not unusual to find the tool chattering on your first try. A good cutting oil is mandatory for smooth cutting. If chatter develops using the 45 degree tool, the best way to cure it is with a 45 Degree Muzzle Lap (#080-624-045). You can chuck this tool in your electric drill and with a good lapping compound it will remove any chatter left by the 45 tool. I strongly recommend this lap because it is very common to get chatter when the cutter is interrupted by the lands of the rifling. In fact, I had to use it on the crown in the photo to get it smooth enough to suit me. This was a 98 Mauser 8mm barrel with a good deal of damage at the crown. After filing it flat, facing it and putting in the chamfer, it’s ready to shoot again.


Muzzle faced, chamfered, and lapped smooth. Outer rim has had edge broken with a file.

There are two basic types of crowns you can make with these tools depending on the cutters you buy. You can use the 90 degree cutter to true up the muzzle and then go in with a 45 degree tool to cut the transition from the rifling to the face. You can also use the 11 degree cutter, which is supposed to be the optimum angle for a crown with regards to accuracy. The 11 degree face can be done partially and the rest of the face left at 90 degrees, or you can take it out all the way to the diameter of the barrel and simply chamfer or round the outside edge. As with other aspects of a custom gun, everyone has his or her idea of what works best.

After all, if you look at a number of factory guns you’ll see that even they don’t agree on a type of crown. Regardless of which style you decide to go with, the gun will shoot well as long as the job is done properly.

Those of you lucky enough to own or have access to a lathe are probably going to start with a contoured blank, turn the threads yourself, then chamber and crown the barrel. For the benefit of those who have never done this before I’ll give you a brief description of how I go about it.

To begin with, I always put the barrel in a four jaw chuck. This assumes you are able to put the barrel through the headstock of your lathe. If you can’t, you can put the end of the barrel in a steady rest and chuck on the smaller portion. Whichever way you do it, be sure your setup is as solid as you can get it. We don’t want anything to be loose. In the chuck, I always use steel or brass shims keep the jaws from leaving marks in the metal. The four jaws allows me to indicate the barrel to center by loosening one side and then tightening the jaw opposite until our barrel is centered exactly in relation to the rifling.

Centering the barrel in the 4-jaw chuck.

A dial test indicator is held in the tailstock and the needle is placed in the bore. With the lathe in neutral, you can slowly spin the chuck with the barrel in it and watch the dial on the indicator.


Indicating on the rifling to center bore exactly.

The needle on the dial will jump up and down as it goes over the lands and into the grooves of the rifling. I always adjust the chuck jaws until the reading is the same when the probe is in the grooves, or when it bounces down to its lowest point. With a good barrel all of the high points and the low points will be exactly the same on the dial once the bore is on center. Still, a half a thousandth off here or there won’t make much difference in the finished product.

With the barrel running true, the shank is turned to size and the threads are cut. We don’t have room for a full description of that here; it would be an article to itself. If you want to learn more about lathe operations take a look at these two books: (#435-100-001) and (#926-000-002). Machine operation for gunsmiths may be a subject we can tackle in the future.

The threads on the Mauser are cut with a 55 degree tool instead of the usual 60 degrees on most other barrels. Brownells carries a special lathe bit (#080-658-125) to make the job easier. In all honesty, thousands of Mausers have been rebarreled with ordinary 60 degree threads on the new barrel with no harmful effects. Many of you have already done it and know it will work. Still, the 55 degree threads will give a better fit and more contact area between barrel and receiver threads. I heartily recommend you get the proper tool or grind your own to 55 degrees. It’s a small detail but worth doing to stick with the original design specs. And I must admit, those 55 degree threads do feel a bit smoother when I screw the barrel into the action. Maybe it’s just my imagination, but…

With the proper threads in place the action should screw on easily but without much looseness or play. I believe the technical word is “slop”. Now we can slip the lathe into low gear and begin to ream the chamber. There are a couple of ways to hold the reamer during this operation. One is the Manson Floating Reamer Holder (#513-054-001) held in the tailstock.

Reamer in the holder and ready to chamber.

The other is to hold the reamer in a tap handle with the end resting on the center on the tailstock. This is my preferred method because it allows the reamer to be taken away after each pass and thoroughly wiped, brushed, or blown free of the chips that collect between the blades. A good cutting oil is applied to the chamber and the reamer to insure smooth cutting, and the reamer is eased into the turning barrel to begin cutting.

The speed of the lathe and the amount the reamer can be advanced will vary according to the caliber being cut and the rigidity of the machine. The general rule is to cut until the reamer flutes are almost full of chips, then clean the reamer and the chamber and make another pass. A straight-walled chamber like the .357 Mag can be cut in a few passes. A .30-378 Weatherby may take 30, 40, or 50 passes before you get to depth. If doing more than one barrel on the same caliber you may want to use a roughing reamer to speed things up. The rougher is used before the finish reamer and will generally cut faster, leaving a slightly undersized chamber that can be quickly brought up to size with the finisher. It also saves wear and tear on your good finisher when many guns are going to be made for the same cartridge.


Measuring the gap between barrel and receiver
shows how far is left to go.

When you feel you’re getting close to proper depth, take the Go gauge and put it in the chamber. On average, the distance from the bolt face to the rear shoulder of the barrel on a Mauser 98 is .110” give or take. It may be a bit more if you’ve cut the bolt face to true it, or less if the lug recesses have been machined back to fix them. Once you get to within .050” or so it’s time to take things easy. Ease back on the amount you cut on each pass and measure often. When you get to within .020” the action can be screwed on with the bolt and Go gauge in place. (You did hide the No Go gauge didn’t you?) A feeler gauge can measure the gap between the receiver and the barrel shoulder, just like we did for the pre-fit barrel. At this point you can ease the reamer in until contact is made and dial in the correct amount using the graduations on your tailstock. At this point you should be at the correct headspace depth. When the bolt will close on the Go gauge you can take the No Go gauge back out of seclusion and try to close the bolt on it. If it won’t close, we’re done. All that remains is to chamfer and polish the sharp edge of the chamber to promote smooth feeding and polish the inner walls for good extraction and overall appearance. Once you’re satisfied with the job, you can turn the barrel around 180 degrees and work on the muzzle.

I normally cut the barrel to length with a hacksaw, put it in the lathe, and indicate it in on the O.D. (outside diameter if you’re new to this) Then the barrel is faced off at 90 degrees and is ready for crowning. The crown is cut with a small lathe bit using the compound rest set up at various angles to do the job. It seems to work best if you start in the bore and work your way out, as this reduces the chances of forming a burr on the edge of the rifling. If a rounded hunting style crown is preferred, we have a specially-ground lathe bit (#080-658-250) that will cut a commercial style crown.
Bolt will not close on the No Go gauge, but will on the Go gauge.

Once the cutting is done, I like to turn the barrel at high speed and polish the freshly cut areas with emery cloth, being careful to stay out of the rifling as much as possible. At that point, the barrel can be removed and a few patches run through it to remove all of the chips, oil, and gunk that have no doubt accumulated in there from the chambering and crowning. Then mount the barrel in the barrel vise, tighten the receiver with the correct action wrench, and try the Go gauge again, just to be sure the chamber isn’t too tight.


Tightening the barrel to the receiver.

Now is the time I like to bolt on the trigger guard and run some dummy rounds through the action to check the feeding. As long as the new cartridge is somewhat similar in length and diameter, they will usually work well in the 98 Mauser actions. Some of the shorter cartridges like the .308 Winchester or the .243 can, believe it or not, be reluctant to feed until some work has been done on the feed rails. This is another area that could take up an entire article by itself, and I suggest you refer the Mauser Shop Manual by Mr. Kuhnhausen, (#924-400-098), to learn more about the many problems that can arise when trying to make a Mauser function with a cartridge for which it wasn’t designed.

Speaking of other cartridges, I just realized I forgot to mention opening up the bolt face for magnum conversions. This is most easily done in the lathe with a specially ground bit, (#080-659-250). Hopefully you are planning on replacing the bolt handle to do this, because it is much easier to chuck up the bolt body in the lathe once the handle has been removed. I have done this job with the bolt held in a steady rest but this setup is not nearly as solid on the average gunsmith lathe as having the bolt back in the chuck. Naturally, this should all be done before chambering begins to allow correct headspacing. The same bit will clean and true the bolt face if it has pitting or damage of any kind. You can’t always count on the bolt face being pristine on a military rifle, even if the rest of the rifle looks great. This can be due to primer leakage and the corrosive priming compound used in much of the world’s military ammunition. It pays to inspect this area closely when shopping for an action to rebarrel. If need be, however, it can be quickly fixed in a lathe with the above-mentioned bit.

Well, we now know two ways to put a barrel on a Mauser; the traditional lathe method and the do-it yourself, pre-fit barrel method. Both have their advantages depending on the equipment available to the gunsmith, and both can give you a 1 st class custom barrel job on your action. Those of you who did the pre-fit barrel, take a break. Those who used the machine method can clean the lathe up and then take a break. Next time we’ll try to get some scope mounts on the receiver without getting them crooked and maybe start whipping that stock into better shape as befits a gun with a custom barrel. See you then. Oh, and by the way, click here if you have any comments or suggestions. We still have a lot of ground to cover and I can use all the help I can get. Plus, I’d like to hear how your projects are coming along.

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