An 'Artillery' Nambu and Lahti

[sheepherder]

A faux 'Artillery' Nambu and Lahti !!!

Disclaimer: I am not a gunsmith; I'm a gun hack. I'm not a collector; I'm an accumulator. I am not soliciting work; I have enough to last me the rest of my life. I only work on projects that interest me; I loathe 'production' work. My small essays are not meant to be tutorials; they are intended to spark interest in others who would like to experiment with unusual features but are hesitant to try something new. There is no one way to do something; there are many ways to skin a cat...

Note: Although this thread is specific to the Nambu, the techniques can be (and have been) used for Luger pistol barrels.

Through the years, there have been threads/posts regarding the Japanese Nambu Type 14 pistol. Several For Sale Nambu's, a few questions, some owner pictures. Lately, probably because of several magazine articles, the Nambu has regenerated interest. I have been intrigued by the Type 14 since the 70's. Recently, some members here selling their Nambu's have finally goaded me to buy one. It's pretty interesting, but as always, I was curious as to how it would look/function with a longer barrel, and in a more familiar caliber.

So I took a poll, first pic here. What barrel length was most appealing. Finding the results of that poll, I started another - Which of two 'artillery' lengths, and which rear 'artillery' sight? I have installed both the Luger artillery and the Mauser C96 rear sights on 'artillery' length Luger barrels.

I gathered my supplies (second pic), and set off.

The third pic shows the receiver preparation. Cutting, drilling, and tapping. Also along the way, several special 'Nambu-specific' tools/jigs/fixtures had to be made; they show up in pics here & there.

I'll be chambering this barrel in the 7.65mm Parabellum caliber ["30 Luger"]. The specs are close to the OEM 8mm Japanese cartridge, and I happen to like 30 cal bottleneck cartridges.

[sheepherder]

More receiver work...Tapping the barrel hole, and checking the bolt to make sure it is centered...It is!

(I don't power-tap; the tailstock simply holds the tap inline with the drilled hole).

[sheepherder]

Moving on to the barrel blank. It's from Green River, 308 cal, 4140 steel. Button rifled.

It's skim-cut for concentricity and inserted as far in the chuck/headstock as it will go...About 5 inches. I turn the end for the receiver stub, thread it, and make a nice snug fit. Then I relieve the last .030" where the stub threads into the receiver.

[sheepherder]

Chambering has been outlined in two previous threads -

Artillery Barrel Specs

http://forum.lugerforum.com/showthread.php?t=21048

and -

Alternative Artillery Barrel Fabrication

http://forum.lugerforum.com/showthread.php?t=25858

- So I won't repeat the steps here. Stripped bolt is used to set headspace and breech gap. Barrel is then removed and the middle is rough turned. The barrel is also milled flat on all four sides where the rear sight base will be, and then is set back in the lathe to turn off the front sight base section.

(The battery in my digi-cam crapped out while the milling operations were going on; my apologies).

[sheepherder]

Here's another thread on barrel fabrication & profiling -

6" .30 Luger barrel, 1900 style

http://forum.lugerforum.com/showthread.php?t=29518

Sometimes you get ahead of yourself...Which is what I did here...I left the muzzle nice & long to chuck it, but forgot that I needed to finish the muzzle [turn to dia, round, and crown] before milling the sight bases round...So I had to cut the excess off and finish the muzzle...

I used a 4-jaw chuck. Took about a half-hour to get the barrel centered.

I don't recommend this setup; I don't like the end being unsupported while it is being turned, but due to CRS it turned out this way. I took very small cuts and slow manual feed, and it turned out OK.

The centering in the 4-jaw is a PITA. It has taken me an hour in the past, to get it down to +- .001". This time I clamped a 7.6mm ground pin in my tailstock Jacob's chuck and hung the barrel on that, and ran the jaws of the lathe chuck up to the barrel for a rough centering. Then it was just all trial & error with the dial indicator to get it 'just right'...

[sheepherder]

Finishing up the muzzle. Clamping the barreled action in the mill and cutting the base, cutting the dovetail, and fitting the rear sight base. Worked out pretty well, I think. I'm using a Luger artillery rear sight. Doesn't look too bad.

[sheepherder]

First pic is just a mockup of artillery sight on blank; next is trimming back the excess metal where the sight mounts; third is cutting the barrel taper, a long tedious manual task, fourth is the tapered barrel, lightly polished, with sight mounted to see how it looks...

I am not a metal finisher, so there will be rough machined surfaces. These should blend in well with the rough Japanese machining...

Other pic is the polished taper...Compare with pic in previous post...

It's getting there...

[sheepherder]

I'm using the rotary indexing head now. Cutting the front sight base, cutting the rear sight base major diameter. Very tedious work. 4º cut at a time. (One rev of the indexing crank).

I'm not happy having to set the indexing head & chuck on one end of the barrel and do my cutting at the other end. But there's no room behind the work table, and the indexing head only has right-hand crank.

[sheepherder]

Here's a sneak preview for all you lurkers...

Fresh out of the indexing head...No front sight blade yet; still mulling that over...have to check with Tom Heller on a blade...

I may narrow the rear sight base 'floor' as well...And chop about 3/32" off the muzzle...

But essentially, it's all roughed out!

Second pic is the barrel + sight mounted on the frame but one turn less than torqued...

I have a 'round' trigger guard coming, as well as another receiver; I'll take a pic with the round TG just for S&G...

[sheepherder]

Here I'm cutting the muzzle back 3/32", crowning, facing, and chamfering. Then it's on to the barrel vise. I had to stop and make a different vise insert, with a tapered hole, and modify my previous vise insert by milling 1 1/4" flats on the sides to fit the receiver. I put a 'notch' on the Nambu receiver to facilitate alignment. Finally, looking at the mounted barrel.

Still mulling over milling 'flutes' on the sides of the rear sight base. Front sight base has to be milled down .050" for the front sight blade, and a dovetail cut.

[sheepherder]

The parts I need to finish the Luger rear sight and the barrel front sight blade for the Nambu are not available (to me), so I need to make my own...

In the meantime, I decided to resurrect an old 9mm barrel blank that I tried to make into a 6" barrel some thirty years ago...That's it in the pic, third one down...I needed to re-cut the front sight band with the rotary indexing head before I took the head off the mill...Bottom of the four barrels is the finished re-profiled 6" barrel, ready to go...I copied Ithacaartist's custom 6" barrel...

Second pic is cutting the feed ramp on that barrel...It is already chambered and extractor notch cut...

I'll start on milling a front sight blade for the Nambu next...

[sheepherder]

I had an eBay vendor renege on a sale, so I had to hunt down some parts I need elsewhere...I'm waiting for parts from three eBay/GB vendors, a Brownell's order, a Numrich order, and a Travers tooling order. Backorders galore!

I managed to get the front sight dovetail cut, and milled the 'scallops' for the rear sight. Not quite like the Luger artillery, but 'good enough'...

Next I need to drill out the Luger rear sight blade & base for an inch pin (no Metric available) and drill a dimple for the re-drilled base setscrew (inch again, no Metric available).

For all practical purposes, the barrel itself is done. I do need to mill a front sight blade and press it in place, and then mill it to shape. That will come next.

[sheepherder]

Although I had said the barrel was 'finished', I forgot about the extractor notch and the feed ramp...I finally got the chamfering cutter I wanted to cut feed ramps with...

Machining the front sight blade and pressing it in place and final machining is shown in next pic...

[sheepherder]

Continuing to machine the front sight blade in place...

Blade height fixed & milled; squared off front sight blade; milling the 'ramp' on the blade.

Second set of pics is the finished faux front sight blade. I set the height of the front blade equal to the height of the rear sight, as that is how my Luger artillery rear/front sights measure up. I assembled some of the special tools I had to make for this project. Finally, a shot of the barrel being torqued in place in the Nambu receiver [barrel extension], using three of the special tools.

[sheepherder]

This project is officially finished. All the machine work is complete. I am quite satisfied with the final product.

I have determined that it would be relatively simple to convert a Luger artillery barrel to fit on a modified Nambu barrel extension ['receiver']. All it would require is to turn the Luger barrel threads down and re-thread; and cut, drill, and tap the Nambu barrel extension to accept it. The chamber might need to be deepened, and the Nambu extractor cut and feed ramp machined.

My 'artillery' barrel is not a direct copy of the artillery Luger. I like the Luger 1900 barrel band/base, and the Lahti 'square' front sight blade. My Luger artillery rear sight had been modified by a previous owner to a square notch, so I made my front sight blade squared also. A "Patridge" sight combination. Similarly, it was easier to make the rear sight base simple rather than the complex concave & convex base of the Luger.

If it wasn't that I wanted the barrel in 30 caliber Parabellum, I would have modified a Luger barrel. I have only seen one 30 cal artillery Luger barrel for sale on GB in the last ten years, and it went for big bucks.

It would also be relatively simple to install a 'stock' Luger barrel of either caliber on a Nambu, using the method I outlined here. A 4 3/4" [120mm] Luger barrel in 30 caliber is almost a dead ringer for the OEM 8mm Nambu barrel profile.

I have to admit, this 'artillery Nambu' is even uglier than the original Nambu.

[sheepherder]

- The front sight sides were cut with a radiused end mill (first pic)

- Nambu receiver/barrel extension has a 2.5mm x 8mm flat milled next to barrel shoulder for alignment purposes (second pic)

- 120º chamfer cutter used to cut feed ramp

- 40º Harvey dovetail cutter used for front sight blade; 60º dovetail cutter used for rear sight base

- The Luger artillery rear sight sits higher than the original grip-frame Nambu rear sight, so milling the Nambu rear sight off was not necessary

[sheepherder]

I was asked if I was planning on making any more 'artillery Nambu' barrels. No, I am not. This was a 'design exercise', and I made it in 7.65mm Parabellum caliber because I like that caliber and it is similar enough to the 8mm Nambu dimensionally and ballistically to make tailoring my handloads fairly easy.

The 9mm artillery Luger barrel could easily be adapted to a modified Nambu barrel extension, with the same dimensional adaptability as the 7.65. It would be relatively easy if you had access to an engine lathe to turn down the Luger barrel thread, re-thread it, and re-chamber it; and a milling machine, to re-cut the extractor notch and feed ramp. A chambering reamer would be required too, in most cases.

The Nambu barrel extension would need to have the old barrel cut off, face the cut, and drill, thread, and relieve the extension. This can all be done in a lathe.

The advantage of the artillery Luger barrel is its thick shoulder. This allows for indexing the front & rear sights to the Nambu extension without cutting into the barrel taper.

A 'standard' Luger barrel, in 7.65mm or 9mm, could be adapted to the Nambu extension, but more care would be needed because of the narrow [relative to the artillery) shoulder. The 4 3/4" pencil-profile Luger barrel is a dead ringer for the OEM 8mm Nambu barrel. It would look almost original.

I made my 'artillery Nambu' barrel with the 1900-style barrel band and Lahti-style front sight blade because I like their looks. The Luger front sight is actually more like the OEM Nambu.

I would select the 9/16" x 24 NEF thread size for the Luger-to-Nambu barrel stub and extension. The Nambu bolt is ~.702" dia and the OD of the extension is ~.862". 9/16" would give an extension wall thickness of ~.150". If the Luger thread of ~18mm x 20 were used, the wall thickness of the Nambu receiver would only be ~.077". That's kind of thin to me. I wouldn't go up to 5/8" thread because that would not leave me much of the original breechace for the bolt to bear against.

Below is an additional pic showing the OEM Nambu two-section feed ramp and bolt face compared to the 'artillery Nambu' feed ramp.

[sheepherder]

I always try to use a 'spare' barrel/barrel extension for my projects. This is because if I make a mistake, it's not the end of that handgun.

A word or two on Nambu 'interchangeability of parts'...There is none...

I used eBay/GB parts for this project. Here's my take on that...

It would seem from my observations that the Nambu is pretty much part-matched, and any interchange of parts will require some searching and trial-and-error matching or hand fitting.

Parts that I've noticed that require particular attention are -

- Barrel extension and locking block. Locking block must be able to fully retract (a straight line) or it won't even allow the barrel extension to be assembled.

- Bolt and cocking knob. The knob, when fully screwed on, must line up with the firing pin extension.

It would seem that the best solution is to get all the relevant parts from the same handgun.

[sheepherder]

Diary Of A Mad Housewife...

[sheepherder]

I was asked WTF that scribbling above is...

It's part of my simple math to decide which size tap to use for the Nambu barrel thread...The left half compares 1/2", 9/16", and 5/8" thread diameters with the Nambu receiver to decide on the best compromise tap to use...(I'll thread the barrel to match the tapped receiver)...

The right side compares different ways to determine Luger barrel thread crush factor...Some say 'extractor notch width', some say 1/16 (or 1/8) revolution of the barrel, and "the book" says .003" (which can be measured with a feeler gauge)...I compared them all, given that the Luger uses 20tpi and 1/8 revolution is un-lapped, while 1/16 rev is 'lapped in' by being tightened & loosened at least three (preferably more) times...

The yellow post-it shows common NEF (National Extra Fine) thread pitches and the corresponding dimension between threads...

I frequently do my calculations on the backs of envelopes and when I can see ahead a step or two I abandon the envelope and go directly to the lathe/mill...Leaving the written account unfinished...

Below is my final comparison of the three tap sizes. Because the Luger barrel thread is ~.708" dia and the Nambu bolt is ~.704" dia, I decided not to use the OEM Luger barrel thread...It would not have left any boltface in the receiver. In a perfect world, I would want equal wall thickness for the barrel stub and receiver front. Or in this case, barrel stub and bolt recess diameter. That would give me 35/64" wall thickness for each. There's no corresponding commonly available tap for that, so I chose the closest tap giving any extra material to the boltface. I want to keep as much of the OEM boltface as possible. It simplifies things considerably (headspace, breech clearance, locking block engagement, etc). That tap is 9/16" NEF [24tpi].

Some of this math crap gets tossed out, some gets saved...Some gets left around for months and when I come across it, I ask myself...WTF is this???