The 45 Mauser Mystery

Original article photographySource page 10

This article pertains to an issue I ran into when assembling a Mauser 98 adapter kit to convert it to chamber and fire the 45 ACP cartridge.

Before I get into the article at hand, I would like to say that the first kit I purchased from Rhineland Arms (Troup Systems. com) was a true drop-in fit, and the instruction booklet they included with the kit is perfect for getting the carbine up and running in less than a day—minus the minimal stock work needed to get the parts to fit and function, but that will be covered appropriately later on. Notice the two dowel pins and the staggered threaded holes.

You will either need time and patience or a qualified gunsmith, with or without the jig, to properly locate these holes in your receiver. This puts the scope directly over the receiver, so you will need the "sniper" safety wing fitted to prevent the wing from hitting your scope. Notice toward the ejector there is a step machined into the mount. This is on both sides to allow flexible mounting options but that step had to be bumped back by 3/16" on the opposing side to allow flush mounting on the receiver.

This article covers the second kit I purchased from them. The threads on both the receiver end and the muzzle end were both oversized. It was evident that while the thread pitch was correct, the root diameter was just slightly too large. My final tally was 0.007" too large. While that number doesn’t seem like a very large excess, just the tiniest glut in size of a root diameter of a thread will cause it to bind.

I attributed it to the finish added to the exterior of the barrel as the included Savage-style locknut was bereft of this surface treatment. While I tried to simply chuck it up in a lathe and hit it with a three-cornered file and a thread repair file, nothing seemed to be doing the trick. It just would not go on past a single thread!

I checked the size of the threads in the receiver itself, but I surmised that if the barrel that I just ripped out of there had fit that well, I highly doubted the tenon threads to be the culprit. I measured them with a custom made thread gauge and they checked out, not even a thousandth oversized. I chucked the barrel up in a four-jaw chuck in my small lathe and took the time to dial the bore in to true "0", both rotationally and longitudinally.

Next step was to engage the half nuts to the 10 threads per inch that the 98s are known for, and then gradually dial the tip of the threading tool in until it just scraped the back of any given thread and set the machine’s dials to "0". Side note, I set the compound on my lathe to the standard 60 degrees for threading so I could move in ever so gradually to just true up the existing threads and take tiny cuts off the root diameter, 0.001" at a time until the receiver snugly threaded on.

It did take some of the finish off the one side of the threads, but the receiver covered all of that finish loss. Blue Loctite also covered any finish loss that was outside the lock nut, too. As for the muzzle end, I have a 0.578- 28 thread chasing die that I used on the muzzle end. I had the same finish loss, so I made a custom brass thread protector (as one does not come with the kit), knurled it, and threaded it on.

Original article photographySource page 11

Needed to touch up the threads and cut down the root diameter of the threads to fit into the tenon threads on the action. This was after a successful fit. You’ll notice threads extending past the receiver ring and these are for the Savagestyle lock ring to set your desired headspacing upon assembly. When I got the first kit in, the factory mentioned getting a spanner wrench for a certain size ring to be able to snug the lock ring down.

I have had terrible luck with this, so I took a micrometer to the outside diameter of the lock nut, measured the slot cut into it, and designed a custom wrench to allow me to do this with a torque wrench. I used a water jet to cut the outside contours of the custom tool, a square hole for the torque wrench, and the pocket with an integral finger to grab the slot on the nut. Twenty-five footpounds and some blue Loctite once I set the desired headspacing, and I was back to finishing the build!

I would seriously suggest you do the same, should you have the capacity to do so, or have a good friend or local shop that will make the part for you. Next was the scope mount. I ordered one of the Mauser Scope Mounts for the Large Ring Action directly from Rhineland Arms. This is a great product and I highly suggest getting one to compliment your build. This is especially true if your donor action is one of the many straight handled bolts as the mount allows scope clearance to work the action.

Few things on this planet are as cringe-worthy as smacking your glass with the bolt handle! I took the time to measure all the dimensions to drill and tap the three holes into the side of the action. The one thing I found out was that I would need to bump the shoulder nearest the front-most hole back by 3/16". This would allow the needed clearance to mount the scope base flush to the action and clear the large front ring. Your action may vary, and this may not be necessary.

Note, I used a reproduction SSR mount and shim set from Numrich for the first kit build. The bolt handle was turned down and I felt I had the necessary clearance to allow this setup. Next up, and this may not necessarily pertain to your build, is the wing safety. Both scope mounts used are low profile, placing the scope pretty close to the action, so the factory three-position wing safety will most likely hang up on the scope.

Numrich sells the "sniper safety", more formally listed as the "Safety, Extended, 98k Sniper, Blued- Steel, New Reproduction" at Gun- PartsCorp.com, to avert the scope issue. This is legitimately a fantastic retrofit but be ready to fit it. The included manual does mention that you may or may not need to take a small amount off of the tip of the firing pin.

Ninety percent of the time this is not needed, but the one build I just finished up had an aggressive firing pin protrusion, so I took it out, popped it into a collet in my lathe, and under power I filed off a little bit. I then took some 400 grit sand paper and a Scotch-Brite pad to refinish the tip of the pin. Be extra careful not to take too much off, or to induce too much heat into the tip and anneal the part from its heat treat. Lastly was the stock work.

No matter what stock you plan on using, have a rotary tool handy for the small amounts of trimming you will need to do around the receiver. Consider a barrel bedding tool for the barrel channel if your stock isn’t opened up for the larger military contour barrels. Brownells has barrel bedding tools that make short work of this. As to the receiver pockets, let’s first focus on the bottom metal.

You will need to mark up and cut out two semi-circular pockets in the existing magazine well to accommodate the 1911 magazine release on both sides. You will need to cut these same shapes into the stock itself to allow access for magazine changes. Let’s move up top. Depending on what scope mount you choose to use, you may well need to remove a little bit of stock material where the scope mount would be interfering with the action dropping in as designed.

Take small cuts, and sand off any sharp edges created with at least 120 grit paper, preferably finer. Many thanks to the wonderful folks at Rhineland Arms for a great conversion kit and for making this article possible. AG