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Building a switch-barrel Mauser: in Part 3 (12/10/09 issue), Coffield fitted barrels using a Savage-style barrel nut. Now he sets up the rifle for scope use.

The next step in the project is to fit a scope base and weld on a new bolt handle. I'm opting to fit this rifle with a scope for a couple of reasons. First, I'm gettin' old and I don't do as well with iron sights as I once did. Secondly, a scope just makes shooting easier and allows me to see the target better.

There's also a third reason. If the barrels were fitted with iron sights, I would have to make darn sure they always lock in place in exactly the same spot. I could not be off more than a degree or two at most and even then it would be noticeable as the sights would be canted. By eliminating iron sights, that's not a problem. The sight, in this case a scope, is on the receiver and won't ever move.

The scope I chose is a Bushnell Trophy 4-12x40. This is an excellent scope at a very modest price. You can definitely spend a lot more for other scopes but this Bushnell will do everything I need it to do at a price I can afford. If you're like me, you'll shop around until you can find the best price.

Generally these scopes sell in the $150 range. As far as I'm concerned, that's one heck of a bargain. Over the years I've used a number of Bushnell scopes and I've never been disappointed with any of 'em. If you haven't checked out Bushnell scopes lately, you really should.

By the way, with a 4X to 12X range, this scope will handle just about everything. While the magnification might be a little low for varmints, at the ranges I shoot it really doesn't matter. A 12X scope will provide plenty of magnification on prairie dogs at the ranges I generally shoot, which run from 100 to 300 yards.

For larger game such as deer, I like the lower 4-5X settings. This gives me the magnification I want along with a wide field of view. Around here, in central Missouri, a lower power scope is very effective when hunting in wood lots where you seldom have a shot of over 100 yards.

I opted for a Redfield base and rings. I picked these up at Brownells at the same time I ordered my new bolt handle. The base I selected was the Redfield FN one-piece base. The only major difference between it and the Redfield Mauser base is that the Mauser base has a cut out or relieved area for the charger guide. However, I've removed the guide so the cutout was not needed.

When I initially checked out the fit of my base I got a bit of a surprise. It didn't fit! Actually, I kinda expected that. If you remember, I had contoured the rear ring of the receiver to remove the charger guide. At the time, I noticed I had to grind away more metal than normal.






When the rifle was built, someone had gotten a little heavy-handed in polishing the rear ring of the receiver directly behind the charger guide. Because of this, I had to take off more metal than normal to remove the low spots that remained from this polishing. I still had enough metal, but the top of the rear ring was thinner and lower than normal.

Unfortunately, this meant the rear of the scope base did not come into contact with the top of the rear ring. There was a gap of about .060". This would have been noticeably less if I had also reshaped or ground the front ring, but on this rifle I had chosen not to do this.

Anyway, this was a problem, but not something I couldn't resolve. I could take down the underside of the front of the base, use a shim as a filler, or I could build up the bottom rear of the base. I opted to build up the bottom of the rear of the scope base and then hand fit it to the receiver.

I used my TIG welding outfit to lay some extra metal on the underside of the rear of the base. I did not attempt to build up the entire rear end of the base. Instead, I added metal to the edges of the base and along lines on either side of the rear attaching screw hole.

I then used various files to contour the base to match the receiver. This was not all that difficult, but it did take some time. I had to go very slowly and carefully check the fit of the base frequently. It's always a lot easier to remove metal than to put it back!

I made extensive use of Dykem machinist layout fluid to monitor just where I had contact. Again, fitting a metal part like this is not difficult if you just go slow and constantly monitor your work. As I approached completion, I began to use my caliper to take measurements from the top of the base to the bottom of the receiver at both the front and rear of the base.

When I had a consistent, uniform measurement at both the front and rear of the base, the job was done. Having the same measurement indicated the top of the scope base was parallel or flat and even with the bottom of the receiver.



The next step was to drill and tap the receiver for the scope base. This was done using a Forster Universal Sight Mounting Fixture. The one I use is the same one I bought more than 35 years ago when I opened my first shop. In fact, this was one of the first tools I bought, and goodness knows how many times I have used it to drill and tap receivers and barrels for sights. It's not a cheap tool, but it's one of those items that once you buy it, it'll last forever if you take care of it.


The advantage of this tool is that it holds the barrel between two adjustable "V" blocks to ensure the scope is aligned with the bore axis. Some other drilling and tapping devices work only off the receiver. The problem is that barrels sometimes are not perfectly aligned with the receiver.

This often leads to having to use up all of your internal scope adjustment when you sight in the rifle. I remember an early Remington 742 that came into my shop years ago with just such a problem. That sort of thing has never happened to me when using this Forster Sight Mounting Fixture.

If you run into a problem getting your drill to cut into the receiver, you'll probably have to spot-anneal it. Mauser receivers often have a shell of super hard metal. That's normal. The manner in which the Mauser receiver was heat treated was to harden the outside of the receiver while leaving the inner metal or core fairly soft.

I had to use an oxyacetylene torch to carefully heat the three spots where I needed to drill and tap. These spots were heated quickly to a red color and allowed to air cool. You don't want to heat any more metal than absolutely necessary. It shouldn't take more than a few seconds at most.

When you drill and tap, you will probably cut into the threads of the barrel. That's not a problem. However, when you fit your base screw make darn sure it doesn't extend into the threads! If you do, you'll have made your switch barrel unswitchable!

Once the receiver was drilled and tapped, I installed the scope. I ended up using Redfield high rings. I normally want to mount a scope as low as possible. The lower rings result in less stress or "whipping" of scope when the rifle is fired. It also helps in shooting, as your face is generally better supported by the stock.



However, the height of the rings is ultimately determined by the diameter of the front and rear of the scope. In this case, I had to raise the scope to clear the barrel and the bolt.

With the scope mounted, the next step was to weld on a new bolt handle. The military bolt handle was bent down, but it would not clear the scope. Also, it just didn't look right with a sporter stock.

When I ordered my scope base and rings from Brownells I also ordered a Lenard Brownell bolt handle. Brownells has been selling these handles forever. They have a nice custom look and are designed specifically for sporters such as the one I'm building.


It didn't take long to cutoff the original handle, fixture up the bolt body and the new handle, and TIG weld it in place. The most time consuming part of welding on a new bolt handle for me is setting up the new handle in the welding fixture.

You want to make darn sure you have the new handle positioned properly. That just means a lot of tinkering and readjusting. The important thing here is to take your time. Don't get in a rush to crank out the welding torch. No matter how much time you take, it will be less than what you would spend if you have to cut the handle off and do it all over again!

TIG welding is especially helpful in a situation like this as you do not get the bolt nearly as hot as you normally do when using oxyacetylene. Also, the weld is much cleaner, with little or no scale.

This is because the electric are generating the heat to melt the steel is enclosed or shielded by argon gas. Without oxygen, this steel can not burn and develop scale. TIG is a tremendous tool for the gunsmith and fortunately, the price of TIG welding outfits,-like so many other electronic items, has actually gone down over the years. Outfits like my Miller Maxstar 150 STL are actually very affordable and well within the budget of most small shops and many hobbyists.



While TIG welding will not get the bolt body as hot as traditional oxyacetylene welding, I still used a heat sink in the bolt to help keep the locking lugs cool. The threaded heat sink also helped to prevent scale on the threads inside the bolt body.

Once the welding was completed, I allowed it to cool and then removed the excess with files. I also used this opportunity to do a bit of cosmetic shaping to the bolt handle. It didn't take long, as the Brownell handle is well designed and in my opinion, very attractive.



I needed to notch the stock for the bolt handle but before I did that, I wanted to bed the action. The inletting on my Boyd's stock was very good. In fact, the action had dropped in with virtually no fitting.

However, I always like to use synthetic bedding. This ensures a perfect match between the wood and the action. There is no way the average person (or gunsmith for that matter!) can duplicate the fit you get with bedding. Also, the bedding acts as a seal for the wood under the receiver.

Over the years this will help keep oil and solvent from soaking into the wood which can cause significant damage. In fact, this can actually ruin the stock as the weakened wood cracks and splits.

With this rifle, I used Brownells Acraglas Gel bedding. This product has been around a long; long time and I've used it for a lot of stocks over the years. It's a good product and especially easy to use. It's a one to one mix. You just mix equal amounts of hardener and resin and that all there is to it! No complicated measuring or that sort of thing.


Like most modern bedding products, you can also tint or color the Acraglas Gel. I have to admit that when I color bedding, I tend to make it too light. This time I resolved to avoid that problem and I purposely colored the Acraglas Gel much darker than I normally would.

My justification for this is that if I get it too dark, I can always stain my wood and make it a bit darker to match the bedding if the bedding is too light, on the other hand, you're up the creek! There's darn little you can do to fix it in that situation. Besides, the walnut on my stock is pretty plain and will need to be darkened a bit to give it a nice color.

As with any bedding project, you almost always will need to remove a bit of wood where you intend placing the bedding. If you already have a good tight fit, there would not be any room for the bedding. It didn't take much work to do this. I just used a small ball-shaped burr or cutter on my Dremel to take out some wood behind the recoil lug and under the rear tang.

The front, sides, and bottom of the recoil lug were covered with plastic electrical tape. This was done to ensure that I had a bit of clearance between the lug and the stock in these areas. This would later make insertion and removal of the action in the stock a lot easier and it would also help prevent damage to the bedding. The most critical area of the. lug, the rear face, was not taped. Here you want the lug to bear directly and fully against the bedding surface of the stock.

While I want to free float my barrel, I do want to use the bedding compound to seal the wood in the forearm barrel channel. To make sure I have a uniform and consistent space between the barrel and the stock, I also used electrical tape on my barrel. I did not use the tape under the barrel nut or the chamber area of the barrel. I do like to support this part of the barrel, and believe that it helps to minimize stress on the receiver.

I also took the time to apply a bit of modeling clay to fill the cut Outs for the trigger sear. I didn't want any bedding creeping into this slot and locking my action in place, Modeling clay was also used to make sure the 'tiny gap between the nut and the surface of the barrel was filled. We're only talking a few thousandths but it wasn't worth the risk of getting bedding where it didn't belong.

Rather than use my regular guard screws, I used my Forster Stockmakers Handscrews. These "T" hand screws are a lot easier to work with when bedding, as you don't have to try to hold a screwdriver and a Screw at the Same time. Also, the "T" handles make it a little easier to adjust the pressure on the action. The shanks of the handscrews were coated with release agent as I sure didn't want to glue them in the action or to the stock.


Release agent was applied to the receiver and the barrel. Any metal that even might come in contact with the bedding was given a good coat of release agent. While you can use all sorts of products for release agent ranging from auto body paste wax to your wife's Pam cooking spray, I used Brownells Acra Release aerosol spray. It's easy to use and easy to clean up. Unlike some spray products this has an "oily" look when applied so it easy to see where you might have missed a spot.





The final step was to apply some masking tape to the stock around the inletting where the bedding would be placed. I tend to be very generous when I apply the bedding and because of this a good bit will squeeze out from between the action and the stock. By covering the stock with masking tape, it will make cleanup and removal of this excess bedding a lot easier.

With the stock and action fully prepped, I applied the bedding to the stock. I also made sure I put a little bit of bedding directly on the action behind the recoil lug before putting it in the stock. By doing this, I hoped to eliminate any possibility of air holes or cavities in the bedding behind the recoil lug. If you just put bedding in the stock, there is a much greater chance you'll end up with air bubbles or voids in the bedding.

The barreled action and the bottom metal were installed and secured with the Forster Stockmaker's Handscrews. I didn't apply a lot of pressure to the Handscrews. I just wanted the action to be firmly seated. Snug is perhaps the best word to describe it. The stock and action Were secured in a horizontal position for 24 hours to let the bedding cure.

As I expected, some of the excess bedding did flow out from between the action and the stock. I used a wooden mixing stick to clean up most of this. I've found it's always best to do as much cleanup of the bedding as possible before the bedding hardens and cures.

In the next and last part of this series (2/10 issue), I'll finish the bedding, cut a notch for the bolt handle in the stock, and apply a finish to the stock and metal. If all goes well this will complete the switch-barrel Mauser project. I'm really anxious to get this wrapped up and see just how well this little puppy performs out at the range.

Until next time, good luck and good gunsmithing!
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Title Annotation:Part 4
Author:Coffield, Reid
Publication:Shotgun News
Geographic Code:1USA
Date:Jan 10, 2010
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