SCR-ish update

It's funny how fast time gets away from you.  It's been almost two years since I stared my 3D printed SCR style bolt action AR project.  It seemed like I was always waiting for something and time kept creeping by.  In that time I've had a lot of people asking me for the files but I didn't have them ready yet.  None of the people that I gave the files to for beta testing followed through.  I also wasn't super happy with how the safety detent worked, so I wanted to do some more work on it.  I had enough parts to put together a 2nd one of my own, but didn't have the motivation. 

I've also been shopping around for another 22lr to plink with lately.  Then I saw Bear Creek's Black Friday ad advertising their new dedicated 22lr upper.  The lightbulb went off and I bought one.  My SCR style rifle was designed to be a bolt action because there was no room for an AR recoil system, and I wasn't super keen on replicating the real SCR's setup on a 3D printed receiver.  But, 22lr ARs don't need the stock recoil system, it's self contained in the upper.  So, I printed out the receiver and buttstock parts, and pinned on my brand new Bear Creek 22lr upper.  I've gotta say, this thing is great and a lot of fun to shoot.  The bolt/barrel setup is proprietary to Bear Creek, but the mags are CMMG and RTB compatible so mags are easy to get.  The optic is a $30 Amazon red/green dot because I love cheap optics on cheap guns.  I don't have a whole lot of rounds through it yet, and so far it's functioned flawlessly.  I hope to actually get the files posted on Weapons Guild by New Years.

PSG-Done

It happened again, I fell off the face of the internet.  Life, work, and whatnot.  Anyway, back to our regularly scheduled program.

I actually finished the my PSG-1 clone, the PSG-None(because there are no actual PSG-1 parts on it), back in April.  I took the pictures, and then left them to stare at me from my desktop for the next 8 months.  To recap, this is an Apex CETME C kit and barrel on an RTG G3 receiver flat bent on the 3D printed jig I designed, PSG-1 style reinforcement rails made by me, with 3D printed PSG-1 style furniture designed and 3D printed by me.  This is a low dollar build and I've had good results with cheap optics before, so the scope is a $35 CV Life from Amazon with a 3D Printed TPU eye bellows.  I also converted a G3 UB training bolt to use with the DAG blue plastic training ammo(see details a few posts ago).  Without wasting any more words here's how it turned out(clamp on bi-pod just for pictures):

Years ago, I 3D printed a costume prop PSG-1 for a friend.  It wasn't overly accurate, but at the time I didn't really know any better.  Just for kicks here's a picture of the original print I did along with my actual rifle.

Still falling...block

Just an update on my 3D printed falling block rifle.  I had a question on how strong the 3D printed barrel threads will be, or how much force it would take to blow the barrel forward out of the receiver.  Someone much smarter than me did the math on the thread shear strength using the rough numbers for PLA, and came up with a minimum of 6,815 lbf, with "ideal" threads giving me 13,583 lbf.  That's well over the amount of force that the DAG training ammo can generate.

I think I've got my design far enough along that I can make a test print.  I'm not sure what I want to do with the top of the handguard.  I don't really want a top handguard, but it looks like it's missing something without it.  I can't make the front of the receiver smaller or longer because of the barrel nut.  I like the Space Cowboy look, so I might end up with some sort of optic mount(my Savage Axis barrel doesn't have a front sight on it anyway).  

La Llama XV esta completa

I'm done with my little Llama XV 22lr.  After test firing, I cleaned the frame and painted it.  I tried something new with the paint, and I'm not really happy with how it turned out, but it will do for now.  I tried to replicate the nickel plating on the metal as best I could.  I use Rustolium Chrome spray paint and topped it with a matte clear.  It looks ok, but it didn't seem to stick to the print well and it chips super easy.  Next time I'll try a base coat of SEM Color Coat under the top coats because that stuff sticks to prints great.  The entire frame as well as the grip panels are 3D printed and here's how it turned out.  It's easy to forget just how small the Llama XV is when you see it alone in pics, so I included my partially printed full size 1911-ish in some of the pics for scale.

Help! I'm falling... a 3D printed falling block rifle

New project time, because apparently I don't have enough projects going on...

Ever since I discovered the very low power plastic DAG 7.62x51/308 training ammo(10g plastic bullet with a total range of only 300 meters), I've been looking for projects to use it with.  I also decided that I wanted a lever gun of some sort, for no reason I can explain.  And, obviously if you're here, you know I do a lot of 3D printing.  So I decided to combine all three into a new project.  I'm going to 3D print a lever operated rifle specifically for the DAG training ammo.

I want to use as many 3D printed parts as I can, mostly because I don't feel like machining anything.  "Locked breech" and "3D print" don't generally go together, so I decided to go with a single shot falling block action because of it's high strength in a smaller size.  With a falling block, it's easy to get a whole lot of strength without having a massive receiver.  It's also a very simple action with very few parts(and if the print proves to be too weak, easy to replicate in metal).  I'm going to use an AR15 hammer/trigger, and a floating 1911 firing pin(mostly because I have all these parts on hand already).  The DAG training ammo has a smaller case head than standard cartridges, and the action is designed around that so standard 308 WILL NOT FIT.  For the barrel, I'm going to use one from a Savage because of the way it threads into the receiver with a locknut to adjust the headspace.  I'll also be using the 3D printed stock I designed for my SCR style project, mostly because I have it and it fits me well.

Still very much a work in progress, but here's how the action looks so far.  The "H" shape of the breech block gives me four locking lugs and a whole lot of surface area and shear area.  Napkin math using PLA numbers and the Lilja equation says that that the locking block should be able to handle 2100lb of bolt thrust with a safety factor of 2.  I have no idea how much power this training ammo has, but it's pretty wimpy, and for reference a 22LR makes about 900lbs of bolt thrust.  My biggest concern is that the case head might start crushing the plastic on the breechface, and if it does, I'll make a metal insert for it.

Here's how it looks with the breech closed and and ready to fire:

When the lever is opened, it pulls the block down, the nose of the lever then hits the extractor lever pulling the case out, and the block cams the hammer back to half cock(I'll cut a half cock notch into the AR hammer).  Once closed again, the hammer can be cocked the rest of the way with the new lever attached to it and sticking out the side of the receiver(which isn't ideal, but I can't come up with anything else that will work with the AR FCG).

Llamas spit.

I finally got my 3D printed Llama frame to were I'm satisfied with it.  It took 11 tries to get it right.  On a normal 1911, I'd have printed a few, got it close, then fit the parts to the frame like you would with any new frame.  That wasn't an option here though because Llama parts are hard to come by and I can't afford to screw anything up so I basically had to fit the frame to the parts.  

I had a heck of a time with magazines too.  Llama mags are expensive, and I'm not positive that they would work because the Llama grip angle is slightly different from the standard 1911 frame my print is based off of.  I tried to make a printed one...and mags are hard...  I ended up using a Browning 1911-22 mag.  The Browning 1911-22 is a similar size to the Llama, but uses the standard 1911 grip angle.  I had to add a little clearance for the slide stop, and file out the mag catch slot a little to get it to lock it, but otherwise it works great!

It actually works...and I didn't lose any fingers!  I put about 30 rounds through it before tearing it all down for inspection.  I had some trouble with light strikes, about 1/4 of the rounds needed a second smack of the hammer to go off.  New mainsprings are completely unavailable, so I'll take it out and do some measuring to find a replacement.  Because of limited space and unavailable parts, the ejector is part of the printed frame.  Though I don't have many rounds through it, the ejector doesn't show any signs of damage from the shells hitting it.

How to waste a day to save $30

You know, sometimes I do things that don't make sense.  Take the project in today's post for example.  I spent an entire afternoon on this, for the express purpose of saving a measly $30.  I wanted a 5rd magazine for my PSG-None because that's what real PSG-1's came with, and because it just doesn't look right with the 20 rounder.  20rd G3 mags are cheap, sometimes as low as $5 a piece if you shop around.  The 5 rounders though start at $30 for POF, and real HKs are much more.  The POFs are nice enough, but I didn't want to spend $30, so I decided to make my own.

I started with a completely stripped G3 mag and whacked the bottom off.

Then I trimmed some of the bottom to make some tabs to fold over.

The tabs need to be folded over very carefully.  Whatever kind of aluminum these mags are made from, it's fairly hard and will crack if you're not careful.

I also had to shorten the rest of the bits.  I cut off about half of the spring, and shortened the reinforcement plate and strap that go across the front of the mag.  I might take another wind off the spring, but I want to see how this one feeds first.

With everything trimmed,it goes back together like any other mag.  Here we are, one afternoon and 15 rounds less later:

A little Sunday baking

I've got to paint my PSG-None.  As much as I like KG Gunkote, it goes on thin and didn't seem like it would replicate the thick factory HK epoxy finish.  I thought about using Duracoat because it looks great and is easy to use, but it's too cold out for me to spray it.  Since this is a low dollar gun, I turned to Google and settled on a highly recommended low dollar finish, Rustolium Appliance Epoxy.  It's cheap, and reportedly very tough.  Here's how it looked after it dried:

I know what you're thinking, way, way too shiny and HKs are a nice semi-gloss.  But that's ok, it's only the first step.  Even though the can doesn't say so, the internet said to bake it.  The time and temp that you bake it for will affect how the finished product looks.  I settled on 65 minutes at 400°F.  400° is low enough that it shouldn't affect the heat treatment of any hardened parts.  Baking cut the gloss down from "too shiny" to "just about perfect!"

HK G3 UB Training bolt in a CETME

I don't know if you've noticed, but 308 Win/7.62x51 is hard to come by these days, and is expensive when you do find it.  That means I've got practically no ammo for my CETME based PSG-None build, and heck if I'm paying the asking price for what is available.  A lot of militaries around the world have some sort of lower power/cheaper to shoot alternative to their standard issue rifle rounds.  Many have 22lr conversions or 22lr variants of their standard weapons for training.  HK was no exception and 22 conversion kits for HK G3 rifles are available, but they're expensive and not very common.

The Germans came up with another option for the G3.  DAG makes a blue plastic cased training round that uses 12 grains of powder with a 10 grain plastic bullet.  It kicks about like a 22lr, but the super light bullet loses energy very quickly.  It's said to be accurate to 100 meters, and has a total range of only 300 meters.  Still dangerous so treat them like any other bullet, but perfect for plinking, and best of all, it's still cheap(around $.22/rd at the moment). 

A round this weak will not unlock and cycle a standard G3, but they have that covered too.  They designed the UB training bolt, a lightweight bolt without any locking rollers that functions as a blowback with the training ammo.  It's around 5oz lighter than a standard G3 bolt carrier, and the bolt face is around .030" smaller than standard so full power 308 rounds CANNOT be used with it accidentally.  They're also reasonably cheap(around $100 at the moment).  Here's what the UB bolt looks like next to my CETME bolt, note the UB electropenciled on it, and the lack of locking rollers on the bolt head:

So this is great, right?  Cheap conversion bolt, cheap ammo, this sound perfect for...oh, right, G3 bolts don't fit in CETMEs...  The problem is that the bell on the cocking end is too big for the CETME cocking tube.  No problem, I can fix that.  First thing was to grind down the bell mouth, then using some Unknownium™ tool steel from my pile, I turned a new bushing to slip over the end, and used JB Weld to attach it.  The length difference between the G3 and CETME bolt carriers isn't a problem because the UB bolt is made for blowback it doesn't need the cocking handle cam action to unlock the rollers like a standard bolt.

A close up of the bushing, the ground ring is just bigger enough to act as a bearing surface so that the whole bushing doesn't drag in the cocking tube.

I tend to share my guns a lot, and take people shooting that aren't super experienced.  To make sure that people know to use the training bolt with training ammo, I decided to paint it.  I also painted a mag to match so that people know the blue bolt goes with the blue mag, and uses the DAG blue bullets.  As much as I like KG Gunkote, I couldn't justify the price for the little bit I needed so I decided to try high temp brake caliper paint, mostly because I want to see how it holds up.  

A 3D printed PSG-1 style furnature set for your CETME

I didn't use a punny title for this post because I'm an attention whore and a descriptive title will pop up better in Google searches.  This post is going to be all about the 3D printed stock set that I designed for my CETME based PSG-None project.  I'm going to assume that if you're here you know how to print and finish parts so I won't go into detail on that, but it's still going to be a long post(see my previous post on how to make your prints look like not prints HERE).  Also keep in mind that these are not identical to actual PSG-1 parts, they are just a close approximation.  The few necessary HK G3 parts(primarily the recoil assembly) are easy to get and fairly cheap as surplus.  It was actually cheaper to buy a used recoil assembly with a green surplus stock than it was to buy the recoil assembly alone.  This will also help with your 922r parts count too, as long as you print these in the US.

We'll start at the back and work our way forward.  The buttstock is made to work with a standard G3 recoil assembly, G3 recoil buffer, and wood stock G3 sling hardware.  I got surplus wood stock sling hardware kit from RTG.  It was much rustier that the pic, but was also cheap, so I cleaned up the parts and cold blued them.  I cut the pin tubes in half using a jewelers saw because the kerf is only .015" wide and wouldn't remove much material.  I used JB Weld to bond the hardware into the stock

The comb on the stock is adjustable.  The comb has a big tab on the bottom and the stock has a matching slot to keep things in alignment.  It's not spring loaded like a real PSG-1, but it doesn't really need to be.  It attaches and adjusts with a single 1/4" screw.  In this pic you can also see the two 1/2" holes in the back of the stock for some 1/2" hardwood dowels.  Superglue works best for gluing the dowels in place.  On the print, you'll probably have to chase the holes with a 1/2" drill bit for the dowels to fit.

I took some liberties with the buttpad and decided to attach it with screws instead of the spring clips found on real HKs.  The holes are sized for 10-24 countersunk screws.  It is also non-adjustable.  It's printed in Ninjaflex TPU flexible filament to help absorb some of the recoil.  The recoil assembly attaching holes are also sized for 10-24 screws, and it is made to also use the large screw that goes into the buffer from the back side.  Here's how it looks all together(I haven't decided how I want to finish the cheekrest yet, so it's still a raw print, and I need to replace the cheekrest bolt with a button head 1/4-20).

Next up is the pistol grip. The palm rest is adjustable for both height and angle.  You can see how I printed the textured part HERE.  It will probably take a little fitting to work with your trigger housing as CETME's aren't exactly known for their precision tolerances, and I've never tried it on a G3 lower.  The palm rest hole is sized for a 10-24 socket head screw, through on the left side, and threading into the right side.

The next piece isn't part of the stock, but it is printed so I'll include it with this set.  The real PSG-1 uses an expensive Hensoldt scope with a rubber bellows.  I am using a cheap scope, and it didn't look right without the bellows, so I made one.  It will fit on any scope with a 39mm diameter rear eyepiece.  It MUST be printed in TPU flexible material, otherwise you'll break your face when it recoils.  The file is made to print in Vase mode with 0 top/bottom layers so it's only 1 wall thick.  Any thicker than that and it will be too rigid.  It's also got a separate base piece that should be set to non-vase and 100% infill to be used with Cura's Per-Model settings, similar to how the fuzzy skinned grip above was set up.  If you want to be clever and not use the Per-Model method, you can sink the model so that the base flange below the bed, then use 10-15 brim lines on the print to get a similar, all be it thinner, result.

The last piece is the handguard.  The stock and grip will for with either HK or CETME rifles, but the handguard is CETME specific because they use different cocking tubes. This will also work with CETMEs that have the triple frame installed on the barrel if you want the MSG-90 look, or you just don't want to semi-permanently modify your pre-built rifle.  The handguard won't sit as far back on the receiver and may have a bit more wiggle in it, but it will still work. This thing is long enough that it gets printed in 3 pieces.  This handguard makes the barrel free floating(unless you have a triple frame installed).  The pieces of the handguard have holes in them for 1/4" hardwood dowel to align things and hold them together.  Like the stock, superglue is the best adhesive to use here.  Because I have a tendency to shoot until my gun is very hot, I bent up some aluminum sheetmetal to wrap around the inside and act as a heatshield so I don't accidentally melt my stock.  The handguard attaches to the cocking tube with a 1/4" countersunk screw, and an expanding wellnut wrapped in electrical tape inserted into the cocking tube.  It's not a great solution and I'll probably come up with something better in the future, I just haven't gotten that far yet.  If all else fails, a standard 1/4" nut can be JB Welded into the end of the cocking tube.

So, how's it look with everything assembled?  Not too bad.  A lot of little tweaks left to do, but it's mostly done at this point.  I still have to find or make a shorter 5rd mag for it(they are available, but spending $25 on a 5rd mag when surplus 20rd's are only $5 just grates against my cheapness).  I'm going to get some lower scope rings for it too, these tall ones are just what came with the scope and I just don't like them.  I still need to paint it obviously and that may take a while because it's too cold in the garage to paint, and the air compressor hose won't reach to the basement.  I haven't decided exactly which paint I'm going to use yet either, I think I might try something new.

Basic print settings:

Buttstock, grip pieces, and handguard:  7 walls and 15% Gyroid infill, Textured grip section Per-Model settings of 1 wall, 0 top/bottom layers, and Fuzzy Skin turned on.

Buttpad: I used Ninjaflex TPU with 4 walls and 15% infill. 

Scope bellows: TPU, vase mode, 0 top/bottom layers, Base flange Per-Model setting with Vase off and 100% infill.

Thingiverse link, finally:

https://www.thingiverse.com/thing:4787497

The cocking tube

You get some words this time and only one picture(because I forgot to take any more).  Long story short, after pinning the barrel I got the cocking tube installed on my PSG-None.  Properly setting the cocking tube gap is essential for proper operation of the rifle, so I did it very carefully.  Needless to say there are some great tutorials on this out there(Holescreek's is probably the best), so I won't bore you with all the steps and no pictures.  I used an aluminum mandrel as a backer for my welds, and only had the slightest bit of burn through on my welds, causing some drag on my cocking piece.  To clean it up, I used the tool shown below, a 1/2" wood dowel, some sticky backed 80 grit sandpaper, and my drill. 

Catchy...CETME mag catchy.

I actually had a heck of a time installing the mag catch on my PSG-None.  The tutorials I'd been following didn't even mention it, and searching for "CETME Mag catch" yielded tons of posts on how to install a paddle mag release, but virtually nothing on the mag catch it's self.  Since the PSG-1 doesn't use the paddle release found on standard G3s and CETMEs, I don't need to either, and that saves us a bit of work.

The biggest problem is that I didn't realize that none of the mag release holes in the receiver flat were finished, and I couldn't see how it was supposed to work.  You don't know what you don't know I suppose.  Once I did realize that everything needed to be opened up, I set about doing it.  First was to drill the holes for the mag catch shaft.  The left side gets drilled to .238" with  "B" drill, and the right side gets drilled to 5/16".  With the shaft holes the right size, I could see where the arm that catches the mag needed to be. I used it as a guide to scribe some lines, then carefully dremeled the window open.  I left it a little undersized so that I could finish it with a file.  If you make this window too big, your mags won't lock in solidly.

I also couldn't find any good pictures of how all the parts were supposed to fit together, or any explanation of what I did or didn't need because I wasn't using a paddle release.  So here's the order and orientation the parts go in.  Mag catch-spring-pivot bushing-release button(with the pin holding the button on).

Then I couldn't find any good pics of how everything was supposed to look installed either, again because everyone out there was posting about paddle release installation.  So here's how it should look with all the parts installed.  It's tricky getting the spring in place, and it will want to go flying if you slip.  I found it easiest to use a punch to get the bushing and spring aligned in the receiver, then slide the mag catch in.   

Actually getting the mags to fit into the receiver took some work too.  CETMEs and HKs use a nose in, rock back style mag lock like an AK, just slamming it in like an AR doesn't really work.  The front of the mag catches on a little lip on the bottom of the trunion, all the receiver sheetmetal does is keep it from wobbling.  The RTG flat I'm using has just slightly too much radius on the front corners of the magwell so the mags didn't want to fit.  The sheetmetal is very soft so I used a block of wood and plastic hammer to massage the magwell opening until mags fit.  I also had to very slightly shorten the bottom of the magwell to match my mag catch height.  

Because 5rd PSG-1 magazines are expensive and this project is not, for now I'm using standard G3 20rd mags because by golly are they cheap, probably the cheapest surplus mags on the market at the moment.  I'll probably try to cut one down at some point, just to see if I can.  I got some from RTG, and some from Apex.  RTG's "Very Good" mags ranged from little wear so some wear(the worst one shown below), Apex's "Very Good" mags look basically brand new, hardly even showing any shelf wear. Everything I've ever gotten from Apex has been better than advertised(and they're not even paying me to say that!)  This isn't the best pic because it looks like the mag isn't seated fully, but it is.  This particular mag is a little bent(not unexpected for being a 50 year old aluminum military mag, and I didn't want to scratch my nice ones while trying to size the magwell ).