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Time for another build, this time the polar opposite of last year's. I'm looking to replicate a LaFrance Specialties M16K, a weird ultra-compact AR variant designed in the 1980s. Tim LaFrance intended for it to be used by combat vehicle crews or for shooting through the windows of a police cruiser, but the only success it ever saw was showing up in a couple of movies and shows (including Naked Gun 33 1/3, Miami Vice, and Escape From LA).

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Basically, it's what today we would call an AR pistol, using an 8-3/8" barrel. However, there are two funky things about it.

First, it used the 'Twin Cobra Feed' (how's that for an 80s name?) gas system patented by Tim LaFrance. In the 1980s, an era before adjustable gas systems, making a sub-11" AR cycle reliably was a pretty tall order. This system uses two gas blocks and two gas tubes to bleed out some gas and delay its expansion, both allowing the gun to reliably cycle in full-auto and reducing the cyclic rate to a controllable 600 RPM. It looks like there were a couple of different iterations of this system used in the guns, but they all follow the same general structure.

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And second, there is obviously no front sight block. Instead, there's a circular front sight welded to the front of the carry handle. This was intended for 25yd minute-of-man shooting, and I have my doubts about its effectiveness, but for what I plan to use the gun for it should be fine.

mIopGHJ.jpg?1

Other specifics of the gun, in no particular order:

  • Early vortex flash hider, either straight or with 'bent' tines.
  • Custom handguard cap with integral sling swivel mount.
  • Handguards cut down from M16A1 handguards, with vents drilled in the underside.
  • Either slickside or A1 (forward assist) upper receiver.
  • Chromed bolt carrier.
  • A1 lower receiver, with LaFrance markings on the right side, either blank or original A1 markings on the left side, and color-coded fire selection.
  • A1 pistol grip.
  • Aluminum (early carbine) buttstock.
  • On the early guns, most metal parts refinished with dry film lube (not sure which), giving them that grey look.

To translate this into an airsoft project, I'd like to get as close to the real thing as I can, where possible. I've seen a couple of replica builds (example) that use modern carbine-length handguards and standard handguard caps, and build the front sight to attach to the carry handle via the optics mount hole, but I would like to get those two details in particular right. That said, I'd like to avoid modification to an A1 lower, so that I can use it with other builds. The lowers on the real thing weren't modified besides markings, and LaFrance did sell the gun as just an upper, so that's not much of a stretch.

In terms of actual implementation, I'll be using a Viper Tech M16A1 as the base, an 8" barrel also from VT, a Luth-AR slickside upper modified to be compatible, and then real parts for most of the rest of the externals. I intend to refinish the parts with Norrell's Moly Resin in Colt Greyish-Black, which is supposed to match the grey used on early M16s, and should be pretty close in color.

The gas system will be decorative, of course, but I'd like to replicate that relatively low rate of fire. I could just take out the short-stroke buffer and that would get pretty close on propane, but that significantly reduces the recoil, and I think I can do better. Just replacing the VT recoil spring with a WOC recoil spring brings the rate of fire down to 700-750RPM while improving gas efficiency and recoil, and swapping the 3oz real buffer I currently use for a heavier one should bring it down further and increase recoil (at the expense of the efficiency boost from the lighter spring). With the light weight of the gun, I'm hoping I can get it kicking pretty strongly.

Lastly, the handguard cap is the most difficult part, as it was a custom part and I lack access to a mill. So, I downloaded Fusion 360 and started learning CAD, and was able to produce a prototype that I 3D printed in resin:

xS3GWns.jpg?1

I had a pair of M16 handguards that were cracked near the end, so were a perfect candidate for chopping. And with some iteration on the prototype I've got them fitting pretty well. Hubs wanted $250 USD to have it milled out of steel, but Shapeways only wanted $60 for their "steel" print, so I've sent it off to Shapeways. It won't be quite as durable as a milled part, but I've incorporated some reinforcement under the sling swivel to hopefully make up the difference.

Edited by CatgutViolin
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So otherwise, I think I have all the non-VT parts I need to complete the build, minus tubing of appropriate size to fabricate the front sight.

hs0AwWG.jpg?1

Now it's just a matter of actually getting the M16A1 and barrel parts from Viper Tech, which likely will not be until next month, but in the interim I can perform the needed modifications to the upper and start on painting once the Moly Resin arrives.

Edited by CatgutViolin
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this is really cheeky but God please can I have that file for the cap? I want something FIERCE and have dreamed of doing this to my wa frankenpita for ages. 

 

seriously you could are a.mint.selling those. especially its modded handguards.

thanks for all the details!  Gives me a build list.

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If the handguard cap works out I'll definitely be putting it up on Thingiverse. Just need to ensure it actually works as ordered first and adjust the design if needed.

Anyways, I received the Moly Resin, modified the upper, and fabricated a rear sight. After a bunch of careful measurement, I came to the conclusion that the centerline of the front sight needed to be 7-8mm above the carry handle. This is important to get right, as there is no provision for elevation adjustment aside from flipping between the two apertures on the A1 rear sight. So the sight was made from a 12mm OD / 10mm ID aluminum tube, with a short piece of 10mm OD / 4mm ID tube sleeved inside it, and raised by a 1.5mm sheet acting as a spacer.

nVeXZkW.jpg

I filled in around the front sight with more epoxy, then started on painting.

Using the Norrell's Moly Resin wasn't too difficult. I did a couple of parts at once, so they all had to be hung in a toaster oven to get up to temperature, then the resin sprayed through an external mix hobby airbrush onto the hot parts. It is important that the parts be hot so that the spray dries immediately, because it takes 5-10 passes from a hobby airbrush to actually build a solid color. Once that was done, the parts went back in the oven and baked for 300F for an hour. I was a little nervous about temperature fluctuations, since apparently if it cures too hot the grey will turn greenish (and if it's too cold, it won't cure at all), but it turned out fine.

The stuff goes on really, really thinly, so some rough areas of the rear sight that I assumed would be hidden by the spray really weren't, and I didn't have any tolerancing issues with assembling the rear sight or dust cover. You can also see some small bits towards the front of the receiver where I scraped it before curing- it's not like Cerakote where touching the part before curing will ruin it, but it is a very fragile coating before it cures.

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And here's the M16K upper on a black anodized lower, to show how the color compares:

yomqisM.jpg

 

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17 minutes ago, paranoiddroid said:

very nice, that looks as good as JT's refinish and aging jobs.

I actually felt that something seemed a bit off about it, and it occurred to me that military guns don't keep that dead-matte finish in use.

So I rubbed a bit of oil into it and think it looks significantly better. I can see why retro enthusiasts swear by this stuff. It was easier to apply than I expected, and looks to be a dead match for the early Colt grey. I've tried abrading it with hand tools and it stands up to a screwdriver much better than paint, so hopefully it'll hold up in game use.

WgHyAlI.jpg?1

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It's not directly relevant to this thread, but it's using more of that Moly Resin, so I figured close enough.

Anyways- I tried using it to refinish the slide, barrel, and controls on my WE P38, to replicate the two-tone look of post-war Walther P1s (steel slide, barrel, and controls, aluminum frame). I just used a media blaster to scour the parts with aluminum oxide, degreased with acetone, applied the moly resin, buffed off some exposed edges to get a head start on wear patterns, and cured in the oven. I made a point to cure a little hotter and a little longer than I did with the AR receivers, hoping to achieve the greenish tinge that the instructions warn about.

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And sure enough, if I compare to the M16K upper, the higher heat and longer cure time made it come out a little greener, and a very good match for the parkerizing I've seen on issued guns:

wtjuBRq.jpg?1

So yeah, this is pretty cool stuff and I think it'll be my go-to for refinishing in the future. It's a a lot easier to apply than Cerakote, but it stands up to hand tools, and doesn't require any particular chemistry on the underlying surface. Really neat product.

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Well, a few updates.

First, I got the handguard cap from Shapeways, and... it doesn't fit! The cap is undersized by about 3.5%. This is apparently pretty typical for the 'steel' (sintered, bronze-infused) process, and is within their stated spec. So... I've upscaled the file a bit, made some tweaks, and ordered it again. If this one fails too, I'm abandoning Shapeways and will just use a resin print, since it seems the reinforcement I added is sufficient for durability.

Second, I was a little annoyed by how different my moly resin finish looked from some of the examples I've seen on Google. So, not one to leave well enough alone, I put the upper receiver and delta ring back in the oven for another thirty minutes in total at a little hotter than before. This finally gave the hint of green/bronze that distinguishes Colt grey from just, well, grey. It seems that the important thing was not getting the parts to 300F (the stated curing temp), but getting the oven that hot, with the parts being 325-350F by infrared thermometer.

I also took the liberty of spraying and buffing the ratty handguards I chose for the project. That got them looking much nicer, more akin to the used-but-clean condition of the real thing. I haven't decided yet if I'm going to go the extra mile of drilling out the extra ventilation holes in the underside.

And lastly, I got some boneyard ProWin 20-round mags and fixed them up, so now I have some short mags for testing. I've seen the M16K advertised with both 20s and 30s, so it'll be nice to have the option. I've also tested with the WA buffer spring and 4.9oz buffer, and the rate of fire on full auto seems about right. Maybe a bit low, if anything, but removing weight from the buffer will be easy if needed.

So here's the full gun mocked up- using my existing A2 lower, and without an actual barrel.

9k5Bpei.jpg?1

Edited by CatgutViolin
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9 hours ago, Gunnman said:

This is a great project. I really love the attention to detail compared to the real LaFrance.

Thanks mate, much appreciated.

Two new updates for today.

First, I got the replacement handguard retainer cap from Shapeways. It's a smidge oversized, which is fine, but the sling swivel mount- which printed fine on the first prototype- came out filled in with steel. It took a tungsten carbine drill bit, proper feeds-and-speeds, and some colorful language to drill it out, as it seems this printed steel is very hard stuff.

I then sanded a bit to knock out the worst of the rough texture, and finished it and the charging handle with the moly resin.

TuCrmxe.jpg

Next, I decided to bite the bullet and drill out the slots in the underside of the handguards. With some image analysis I worked out a decent approximation of the pattern used on the real ones, drilled pilot holes with a drill bit to rough out the shapes, and then finished with hand files. Unfortunately, the two halves of the handguard are made of slightly different materials and are slightly different patterns, so they don't perfectly match, but I figure it's close enough.

Pay no attention to the cat hair globbed up on there after I made a poor choice of polishing rag.

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And lastly, I got another dirt-cheap carry handle rail and cut it down slightly to clear the front sight, so that I can do goofy stuff like this:

PhlxFnt.jpg

I'm on the home stretch now. Just waiting on the Viper Tech order to finally process (which should be any day now), and that will supply both the A1 lower I want for cosmetic reasons and the 8" barrel I need to make this actually function.

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11 hours ago, aznriptide859 said:

That looks fantastic.

As someone who just downloads .stl's from Thingiverse, how hard is it to learn Fusion 360? I feel like that's a huge obstacle to unlocking much more potential from my 3D printer.

I have some 3D modeling experience so YMMV, but while I got frustrated by certain interactions being unintuitive, there's a lot of reference material on the Internet to turn to. The intended use workflow is fairly intuitive; it's typically about drawing complex shapes in 2D and then extruding into the third dimension.

They don't advertise it much but you can get a personal/hobby use license for free, so it's worth at least giving a try.

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  • 2 months later...

That took longer than anticipated, but the first half of my VT M16A1 arrived. I asked for the lower and parts to be sent first so that I could get going on this project while waiting for the remainder.

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So, I immediately detail stripped it and applied the Moly Resin. It didn't come out a perfect match for the upper, but that's acceptable, and largely unavoidable given that I applied the resin more heavily to hopefully reduce risk of chipping.

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Once the lower was reassembled with necessary fitment modifications (some dimensions need to be tweaked to use the real upper), I got to work assembling the barrel, which took all of thirty minutes.

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Two gas blocks, the front one mocked up to look like it connects to the rear one, and the handguard cap is just friction-fit between the muzzle device and front gas block.

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Then I just polished the bolt carrier to a chrome shine (I wanted VT's chromed carrier, but unfortunately they are at least temporarily no longer offering it), assembled the furniture, slapped in a Prowin mag, and called it done.

Oh yeah, I also forgot to mention that last month I decided the handguards could stand to look better, so I redid the conversion on a repro set.

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I still want an old-style lock ring rather than the castle nut, but those are extremely difficult to find at the moment, so I'll wait.

With a combination of weaker (WA) recoil spring and an H3 buffer, the rate of fire is reduced to a pretty sedate 680 RPM, on par with the real thing. The efficiency is good enough that I was able to clear 117 rounds on semi in the short mag with lockback, in strings of 10 with 10-second pauses between. So, I feel pretty confident the efficiency will be good enough for cooler weather.

Hopefully I'll get some shooting footage tomorrow, and then I've got at least one more accessory I'd like to build for it before I'm finished.

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  • 2 months later...

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