What Shall I Do With That Old Mauser? Part 2

Gun Digest: Kevin Muramatsu converts an old Mauser to 45 ACP.

The tools the author used to re-barrel a mauser to 45 ACP.
The tools the author used for barreling the .45.  A finishing chamber reamer, Go and No Go headspace gauges, floating reamer holder, the rifle’s bolt, Kuhnhausen shop manual on the Mauser rifles, the prepared, painted receiver, and the indispensable depth micrometer.

Last issue we played around with modifying an old 8mm Mauser into a .45 ACP.  It was just one of the mostly meaningless jaunts into guncrafting goodness that turned out to be a fun, creative challenge.  I’ve already completed the magazine modifications and the construction of a new magazine well to make use of .45 ACP cartridges.  The remaining tasks to be done are to fit a barrel to the gun and figure out how to shorten the bolt throw, without of course, cutting out a chunk of receiver (and bolt) and welding it back together.

Getting Started

The first thing to do was the most difficult, or at least the most time-consuming chore. Initially I determined just how far I wanted the bolt to cycle, and where the ejector should be located.  The receiver had a “thumb hole” in the left side to accommodate thumb clearance when using a stripper clip to load the gun.  Basically it was a scoop out of the left side of the receiver just above the bolt rail way.

Cutting the taper is easy with the right compound rest.
Cutting a taper using the compound rest is pretty easy, as long as, like the author, you can temporarily control your caffeine shakes.  Using 180 sandpaper to smooth out the contour after the cutting is done blends it all together seamlessly

I decided to move the ejector up to just in front of this scoop and to make use of that scoop to place the new bolt stop.  In order to accomplish this job, I milled out from a piece of half-inch square steel bar stock a new ejector housing that spanned from the housing screw hole and arms on the left rear of the receiver (where the original ejector housing and bolt stop had been) all the way to an inch or so forward of the scoop.  I then had to make a slot just in front of the scoop so the ejector could project into the bolt way from the ejector housing.

Forming the ejector housing was pretty easy, making measurements with a caliper of the bends, turns, and corners of the receiver, and then milling the block to fit.  The original hole where the bolt stop projected into the receiver and the original ejector slot were used as guides to align the new housing along the receiver.  A small flanged projection fitted in this area to align the housing.  In the “scoop” area I simply left a whole big block of material that pretty much made a false wall in the scoop.  I drilled and tapped a hole near the front of this blockish mass and inserted a quarter-inch long 4-40 socket head screw.

Then I ground a slight bevel on the rear of the tightened screw.  When pushing the bolt forward, the left side bolt lug contacts that small bevel, pushing the housing out slightly and allowing the bolt to pass, while pulling the bolt back forces the lug to impact the unbeveled front of the screw, stopping it in its tracks.  To finish this piece off, I cut an angle on the outside front of the housing and then milled a few flutes into the top, bottom, and left sides of the housing.  I then painted the housing with the same black Aluma-hyde II that covered the receiver.

How to Make it Go BIIING!

Now that the bolt stop had been created, I now had to make the ejector work.  I wanted to keep the original ejector and not have to fashion a new one from scratch.  I milled into the front end of the housing a slot to fit the ejector and drilled a hole for a roll pin for the ejector to rotate upon.  Then I slowly modified the ejector to project out sufficiently to insert itself in front of the bolt when the bolt was fully open.  I made two small cuts in the outside of the ejector, creating a spring guide of sorts for a small spring (just happened to be the bolt stop detent spring from an AR-15).

This spring pushes the ejector against the bolt, forcing the front of the ejector into the ejector slot on the left side of the bolt face as the bolt is pulled back, making contact with the left rear face of the cartridge case head.  Of course a relief hole was drilled in the ejector housing to accommodate the spring.  I effectively did all this by eye in little increments, and it was pretty time-consuming.  In the future, if I do this thing again, I will spec out some measurements based on this housing, but this time I was shooting as I went along.  Fortunately, the housing slot aligned perfectly with the slot cut into the receiver.  This is probably because I did precisely calculate that particular task, and it was rock steady because of the “guides” previously mentioned.  See!  I’m not a complete “wing it” gunsmith.

Frustration and Correction

The completed ejector block.
The completed ejector block.

I should also make note of the ejector housing ears on the left rear of the receiver.  I thinned them out by a few thousands by polishing to reduce the friction back there.  My first thought for a tension spring was to place a small loop spring in between the ears.  That didn’t work.  This tension is, of course, very important as it serves to keep the entire housing flush against the left side of the receiver, and it has to be stronger than the ejector spring that was pushing against the bolt.  This one really stymied me; I had no room or leverage to work with in the back, and there didn’t appear to be any other way to make this work.

Then, with a 100-watt light bulb pulsing above my head, I cut off a piece of the original flat magazine spring, still slightly curved, and about one inch long.  I drilled a hole near one end and used the bolt stop screw to hold it in place on the inner false receiver wall of the ejector housing.  This spring extended back to make contact with the inside wall of the receiver, back where the original ejector entered the receiver.  It was thin enough to not interfere with the bolt, but had enough tension to just barely keep the ejector housing pressed tight to the receiver, and just enough give to allow the housing to be pulled out enough to allow the bolt lug to pass by the stop screw so that the bolt could be removed from the rifle.  This detracted a tiny bit from the clean lines of the gun, as when the bolt was pulled out there appears this ugly foreign-looking flat spring thing.  But it works and that was enough for me.

Last But Not Least

Barreling the gun was vanilla.  I first contoured the barrel down to about what the original barrel’s diameter measured, and made it 16 ¼ inches long.  It’s truly amazing how much lighter a barrel blank becomes after you cut a third off the end and turn it down a bit.  I wanted to make sure that the outside diameter and bore were concentric the whole way so I trued the muzzle end and reversed it, put that end in the lathe chuck and stabilized the barrel with a live center and steady rests on the other end before the final contouring cut. I can say with pretty certain authority that this barrel, unlike ANY you get on a factory gun, is truly concentric.

The ejector block from the left side.  The author was quite proud of the way this assembly turned out, as it looks really darn cool.
The ejector block from the left side.  The author was quite proud of the way this assembly turned out, as it looks really darn cool.

I put a taper in front of the chamber that roughly matched the factory barrel, though not exactly, as the original 8mm barrel was stepped.  On the muzzle I installed a completely unnecessary muzzle break.  I say unnecessary, as a .45 produces little gas to redirect, and the recoil from a .45 carbine is best described as a gentle push.  But it looked cool, so I did it anyway.  I also permanently attached this brake since there would be no reason to remove it in the future.  I threaded it on, timed it to align properly, drilled a hole through it, pinned it, and took it to my gunsmith buddy Mark to weld the pin in the hole (I didn’t have welding equipment readily available, and besides, he’s better at welding than yours truly).

I was also able to cut a superb chamber with minimum headspace thanks to the virgin reamer I purchased from Dave Manson Precision Reamers.  New, quality reamers like this one cut as if the steel was actually butter, as long as you don’t reverse the cut and dull the tool.  Or allow the reamer to get clogged with chips.  Or not use sufficient cutting fluid.  Or feed the reamer too fast.  Or not use a floating reamer holder.

Or think you’re really slick and ream the chamber on high speed.  For the record, I’ve never done any of those things. Ever. I’ve also found that cutting the chamber to just fit the Go gauge before final fitting on the receiver, then tightening the barrel onto the receiver of a Mauser, still leaves plenty of headspace room when complete, pretty much eliminating the need to calculate any crush factor inherent in the chambering process, and removing the need to use an extended shank reamer to finish the chamber after tightening the barrel down.  The No Go gauge still doesn’t even come close to fitting.  I also acquired the Go gauge from Manson, paying for the mistake I made by loaning my previous gauge to another gunsmith some time ago.  Never loan a gunsmith ANYTHING.  It will disappear into his bottomless gunsmith packrat box.

Buy the book Gunsmithing: RiflesTo learn more about gunsmithing, check out the book Gunsmithing: Rifles.

The final duties to perform were to put the gun in the stock, get some kind of sighting system on it, and test it.  I simply added a small section of Picatinny rail to the top of the barrel shank and topped it with a JPoint Microelectronic sight.  This red dot is rather small, rather light, and rather expensive; so I borrowed it.  But it was perfect for the gun and looked pretty neat perched just in front of the receiver.  I suppose I’ll have to buy one of those now too.  Concluding the project, I nailed the barrel with Aluma-hyde so that the entire barreled action was a nice matte black, re-inletted the stock to fit the new barrel and ejector housing, and then put off until later the minor contouring that was necessary to blend the exterior lines.  I just wanted to shoot it.

Okay, this was really cool.  I’ve mentioned before that I’m not a good shot.  But I did put a five-shot group at 25 yards into a single ¾-inch hole, no lie.  The group opened up to three inches at 50 yards.  I blame the 8 minute-of-angle dot in the JPoint.  The dot simply covered the entire target and was thus difficult to center on the bull’s-eye at that range.

Guess that extra concentricity work paid off.

You Know You Succeeded When…

I then showed this project off to a couple friends and then my father and uncle.  You know you’ve done something right when a guy gives you a puzzled “what the heck is that?” look, and shoots the gun.  Then he turns around slowly with a really stupid grin on his face, with a little bit of drool hanging off the corner of his ‘stache, and then proceeds to turn back around and empty your magazine.  My favorite quote was “Hey! You could load this thing up with Cor-Bons and deer hunt with it!”

Well, lookitthat!  I’ve got a practical use for this thing after all!

Read Part 1 of Project 45 ACP Mauser

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