Muramatsu converts a Mauser to .45 ACP in this two-part series. Why, you ask? The best reason of all: It's fun.

Some of the coolest things in the gun world are those with no serious application.  Or perhaps those applications are in the eye of the beholder.  One of the neatest things I have seen is a conversion for an old favorite that is little more than just plain fun.  But that’s good enough for me.  I figured if I needed a “sporting” use for it, I could take it swamp buck hunting with some XTPs.

All You Really Need is Raw Material

It used to be, in the olden days of gunsmithing, that gunsmiths were customizing and sporterizing a myriad of used (sometimes very) military rifle.  Carcanos, Arisakas, Enfields, and Springfields were cut down, welded, gutted, rechambered and rebarreled, sighted and scoped.  However, the most customized rifles were probably the Mausers.  Okay, yes the Springfields and Arisakas were derived from Mausers, derived being the key word.  Mausers didn’t have those stupid magazine cutoffs or the ridiculously difficult safeties.

Mausers came back from Europe by the thousands.  Unfortunately, the 7.92x57mm (8mm Mauser) ammunition to shoot through them was not as plentiful, so many, many of these Mausers were rebarreled or rechambered to shoot something more easily appropriated:  .30-06 Springfield, 8mm-06, .270 Winchester come to mind.  Interestingly enough, many years later when your humble author was in gunsmithing school, he came upon one of his fellow students turning a Mauser into a .45 ACP with a kit that he purchased online.  That kit is no longer available, but I figured it wouldn’t be all that difficult to replicate one on my own from scratch.

I want to point out that unlike most of the stuff done in this column, to do this project involved heavy use of a lathe and mill.  I also removed the original magazine floor plate, spring, and follower and tossed these and the retaining button into the gunsmith packrat box.

How Am I Going to Do This?

First off was the easiest part of the whole procedure.  The case head diameter of a .45 ACP is only slightly larger than an 8mm Mauser.  Using a Dremel tool with a small grinding stone, I ground off a touch from the extractor claw, just enough so that a .45 ACP case would stay held in its grasp.

The second task was to brainstorm how to feed the ammo.  Most gun owners will readily acknowledge that other than the case head, .45 ACP and 8mm Mauser aren’t even close to being similar.  Like in the old kit, I decided to use 1911 magazines as a feeding device because of availability and compactness. I needed to construct a magazine well block that would fit into the original magazine box on the gun yet have a magazine well of its own inside it to accept the 1911 mags.

I needed to figure out a mag catch too.  Well, what I had available was a big block of Delrin plastic.  I milled it out to roughly the right size for the magazine well dimensions but oversized by about 10 percent.  I then cut it in half.  Using a 9/16-inch ball-end mill I cut lengthwise the magazine channel (at a 14-degree angle to match the angle in the 1911 pistol), intending to use the rear half of the block to form the back of the mag well only.

This worked out pretty well and was an easy way to cut the channel. I was then able to carefully use a belt sander to precisely shape both sides together to match the channel, and tightly fit the block to the mag well. I then fastened this block to the mag well of the Mauser by drilling two 1/8-inch holes in both the front and rear of the mag well and pushing through four roll pins.  The block protrudes about ¾ of an inch below the bottom of the mag well, and thus the stock, but I thought that it looked too skinny and rough.  So I fastened two sheets of smooth plastic, one on each side, to the block using an epoxy.  After the epoxy had cured, I again touched up the whole assembly on a belt sander.

Now to make this feed properly, I had to make the magazine sit so that the feed lips were just below the closed bolt of the rifle, but high enough so that the bottom of the bolt face could catch the top of the first cartridge in the magazine. I had already decided to use an AR-15 magazine catch assembly, just to see if I could pull it off.  I simply machined the slot out of the left side of the block and drilled through to the right side for the post of the mag catch.  On the right side, using the drilled hole as a starter, I milled the ovoid hole for the button and then opened the hole up with a 1/4-inch drill until it came to within 3/32 of an inch of the slot in the left side.

This deeper wider hole was to accommodate the mag catch spring.  I had to shorten the spring by half to make it fit properly, as this whole assembly is about half the width of the AR-15’s mag well.  After assuring that this mag catch would function properly, I removed it and inserted the magazine to the proper depth.  Looking through the slot, I was able to mark on the magazine with a scribe where the mag catch slot was located.  I then removed the magazine and with the mill, machined a small slot at the scribed location.  Fancy that, it even worked.  Inserting the magazine into the new mag well should be smooth without too much wobble and some friction should be apparent from the magazine catch until the catch snaps into place in its slot.  I did find that the slot I cut was too wide, so I decided that I did indeed need a stop to keep the magazine from going all the way through the action when the bolt was open.

I dug out a hole in the front left “corner” of the mag well at the top, just deep enough to be level with the notch in that portion of the magazine.  This notch is intended to give clearance for the slide stop in the 1911 pistol, but in this case provided a satisfactory point to place a magazine stop.  I used a scrap piece of steel (in fact, a useless, used and worn AR-15 disconnector), ground down to the proper shape on the belt sander.  I used the original trigger pin hole as a screw hole with which to fasten it to the magazine block.  I duplicated the radius of the magazine front to allow it to protrude just slightly into the magazine well.  After drilling and tapping this hole into the block I screwed down the new mag stop and inserted the magazine to check the fit.  It stuck out a little too much.

So, using a Dremel tool with a grinding stone,  I shortened it just enough so that it would interfere with none of the cartridge dummies in the magazine.  With the magazine set in the well, there was a very small amount of “jiggle” play, which turned out to be insignificant.  The bolt perfectly stripped dummies off the magazine when pushed forward.  In fact, once the dummy cleared the feed lips of the mag, the follower literally popped the dummy right up underneath the extractor.  This was a pleasant surprise.  It was inordinately fun to fill up the magazine well with dummies and cycle them through the action to let them fall out the front of the action.  Sometimes it just feels good to do things right.

I then finished off the whole assembly with Matte Black Alumahyde II from Brownells.  This turned the appearance from warmed over junk to a halfway decent looking gun assembly.  Convenient too, since it is an aerosol and doesn’t require baking, which was good since a significant amount of the assembly was plastic.

So, What's Next?

So now that the magazine block was complete, and it even worked, I needed to move on to the next step.  I decided to leave the barreling until last.  One of the experiments I decided to conduct was to shorten the bolt throw and move the ejector forward so it was just behind the new magazine well.  And of course this little piece wouldn’t be complete without a completely unneeded muzzle break to help tame the mighty recoil.  We’ll detail all this and more in the next excursion into the world of gun goodness.

Click Here to Read Part 2 of Project 45 ACP Mauser

With a little imagination and a lot of skill, you can create a .45 ACP Mauser rifle. It doesn't matter why. This project is just plain fun.

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.

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

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.

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.

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