Building A Mauser Sporter, Part 2
September 23, 2010
Lapping The Bolt, Fitting The Barrel, Finishing The Chamber & Welding The Bolt Handle.
In order to check the bolt lugs' contact with the receiver, machinst fluid was applied to the lugs and the bolt was then worked in the action several times. The bare metal indicates that the area of contact was less than 50 percent.
After World War II, one of the most common activities for the gunsmith hobbyist was the conversion of an obsolete military bolt-action rifle into a sporter. In the earliest issues of Shooting Times, there were many articles covering various aspects of this type of project. As part of the commemoration of the 50th anniversary of this magazine, I'm putting together a sporter using an old large-ring 98 Mauser action. Over the course of the next six months, the project will be completed. If you've never done a project like this, you might want to consider doing one along with me.
Lapping The Bolt
In the first part of this series, I selected an action and made sure it was suitable for this conversion. The next step is to check the bolt lug contact. For the rifle to be both accurate and safe, both locking lugs should bear evenly against the receiver lug seats. This can be checked by stripping the bolt and then coating the rear of the bolt lugs with machinist layout fluid. You then carefully insert the bolt in the receiver, holding it fully forward, and lock it in place. Place your thumb through the front of the receiver on to the face of the bolt, push back, and lift the handle about 15 degrees or so and then lower it. You repeat this about two-dozen times and then remove the bolt from the receiver.
The rear of my bolt locking lugs were inspected, and the spots where there was contact with the receiver lug seats were shown where the layout fluid had been removed. The wear on my lugs indicated I had only about 50 percent contact at most. That's not unusual. I've seen rifles where there was even less contact. The solution to the problem is to lap in the lugs. To do this you apply 320-grit lapping compound to the rear face of the bolt lugs and repeat the process that was used to check the initial lug contact.
When lapping the bolt lugs to ensure maximum contact, the author used a spring-loaded compression tool, which maintains pressure on the face of the bolt and forces the bolt lugs back on to the receiver lug seats.
Because the lapping process entails a lot more short movements of the bolt, I used a spring-loaded fixture that I made years ago to apply pressure to the front of the bolt. It is a lot easier than using my thumb! A variation of this tool is currently available from Brownells. Periodically, I removed the lapping compound, applied some layout fluid, and checked the amount of contact. As I worked, I could see the amount of contact increasing. I finally stopped when I had almost 100 percent of the theoretically available contact.
Fitting The Barrel
After lapping in the bolt, the next step was to fit the barrel. I'm using a short-chambered, prethreaded Shilen barrel that I obtained from Brownells. The barrel was chambered for .35 Whelen, a cartridge I've been interested in for years. It's basically just the .30-06 necked up to .35 caliber. It's a potent hunting cartridge and ideal for large game at close ranges.
Like I said, the barrel I used was short-chambered, meaning that the chamber was not cut to full depth. This allowed me to finish the chamber by hand and headspace it to my action. Barrels like this were not available back in the 1950s, '60s, or even the early '70s. They allow the hobbyist without a lathe to do barrel work and are available in a wide variety of calibers and contours to meet almost any need.
The barrel threads were lubed with an anti-seize compound, and then the unit was turned into the receiver. I held the barrel in my barrel vise, and the receiver was clamped in my action wrench. As with most barreling projects, the barrel is held steady while the receiver is turned on to the barrel.
When extending the "short" chamber, very little metal was actually removed. Note the fine chips in the flutes of the .35 Whelen chamber reamer.
Finishing The Chamber
Once that was done, I checked the length of the chamber with a Forster Products "Go" headspace gauge. With that gauge in the chamber, the bolt would not close because the chamber was too short. The gauge was removed, and a .35 Whelen chamber reamer made by Manson Precision Reamers was used to lengthen the chamber.
The chamber reamer was attached to an extension that allowed me to turn it while the barrel was fitted to the receiver. A lot of cutting oil was applied to the reamer to lubricate it and help ensure a smooth, chatter-free cut.
With a "No-Go" headspace gauge in the chamber, the bolt will not lock fully into the receiver.
The Manson reamer is an absolutely top-quality cutting tool, and it did a fantastic job. I would make about four turns of the reamer, pull it out, clean the chamber, and check the headspace with the Forster headspace gauge. By the way, with the Whelen cartridge, you use standard .30-06 headspace gauges. As I worked, I could judge the progression of the lengthening of the chamber by the position of the bolt handle as it closed on the gauge.
You must go slowly when doing this work. It's easy to cut too much, and if you do, you'll end up with excessive headspace. Fortunately, that didn't happen here, and in very little time I had my barrel completely chambered and fitted to the receiver.
A sporter bolt handle is held in place with a fixture for the initial weld. After that, the fixture will be removed.
One other thing you'll want to make sure you do is to break the edge of the chamber on the rear face of the barrel. If you don't, this sharp edge will scar the brass as the cartridges are loaded, and in some cases it will even cause feeding problems.
Welding The Bolt Handle
The last step was to weld on a new sporter-style bolt handle. I opted for a Brownell handle that was designed originally by Leonard Brownell, one of America's greatest gunsmiths. It has a very attractive shape and is ideal if you later want to mount a scope.
The original handle was cut off, and the new handle was held in place with a bolt-welding fixture. A heat sink was threaded into the bolt body to help control excess heat from the welding process. Damage from excess heat was a major problem when I started gunsmithing many years ago. Back then most gunsmiths used an oxyacetylene welding system. Nowadays, I use TIG for most welding jobs in the shop. There is a lot less risk of damage to the bolt from excess heat, and the welds are much cleaner and neater. If you have someone weld on a new handle for you, try to find someone who has a TIG set-up. You'll be glad you did!
That's about it for now. Next time I'll install iron sights and drill and tap the receiver for a scope base. Until then, good luck and good gunsmithing!
By using TIG (tungsten inert gas) welding, the author was able to get a good, clean weld with minimal heat. Note also the use of a heat sink in the rear of the bolt.