I admit to cheating.

I've mentioned a few times that I've had to draw all the parts for my PSG-None from scratch.  So, how do I do that and get reasonably accurate parts without having any actual PSG-1 parts to measure?  Simple, I cheat.  Solidworks has a feature that allows you to import a picture as a sketch, the Sketch Picture command.  What I do is find the most direct side shot of the object that I want to copy, import it into Solidworks, then scale it to the appropriate size.  For this project, I used the two rear takedown pin holes as my scaling guide, because I can directly measure the distance between those holes on the parts I have.  I just made a sketch with some points the correct distance apart, and scaled the image so it matched.

Then it's just a matter of creating 3D objects using the 2D picture as a guide.  Something to watch out for is if the object in the picture is tipped or has some lens distortion.  In this case, the gun in the picture was photographed at a slightly upward angle instead of a direct side shot, so the stock especially has some noticeable distortion because it's tall and straight.  You have to account for that in your sketching, and fudge as necessary.  Here's what my new parts look like overlaid on the picture I used as a guide.

I tried to be as accurate as I could, but still had to use some artistic license because I don't have real parts to measure.  I spent hours scouring the internet for reference photos and did the best I could without having parts in hand, and they look nice but these are in no way interchangeable with real PSG-1 parts(nor are they really intended to be, if you want a real clone buy real parts).  I also had to make some changes to work with my CETME parts kit, most notably in the handguard so that it would fit with the CETME trunion and cocking tube.  I took a lot of liberties on that one...  Here are what the parts look like without the guide picture in the way.  Just have to print them out and then wait until I get the receiver together to see how they fit.

Something old and something new

It's been cold and rainy and I didn't want to go outside so I got some more work done on the PSG-None.  When I stared this project, I though it would be pretty straight forward because I'd already 3D printed a cosplay prop version of the PSG-1.  Yeah...not so much.  The file that I based my prop on was not even close to accurate, none of it was the right shape and it wasn't even close to something that would fit on a real receiver.  Good enough for what it was as a prop, but not good enough for me to want to use on this project.  So I ended up redrawing everything from scratch.  

I started with the pistol grip since it could be printed quickly for test fitting. While I was at it, I experimented with Cura's "Fuzzy Skin" option.  It's an option in Cure that makes the outer wall of the print jitter randomly, making it look fuzzy compared to the smooth lines of a standard print.  You can see in the picture where the fuzzy skin stops and standard skin starts.  At some point I'll post a how-to for getting the fuzzy skin only in areas where you want it.  Here are my first test pieces, the grip and palm shelf, on my CETME grip housing.  This is basically a rough draft, the final version will fit a little better, and will be a bit shorter.  The bottom of the grip on this print extends too far down.  Also, for what it's worth, I usually use grey for all my prototyping because it's easy to see where things are rubbing and material has to be removed to get things to fit right(just a handy tip for printing things you know you're going to have to file and fit).

After modifying the grip to my satisfaction, I moved onto the stock.  Here too, I drew everything from scratch.  I'm going to be using a G3 recoil assembly and buffer instead of the CETME parts.  I bought a whole recoil/stock unit because it was actually cheaper than just buying the recoil assembly alone, so I have a nice surplus green G3 stock to pull some measurements from too.  After drafting, I printed out the front chunk of stock to make sure it fit in the recoil assembly like it was supposed to.  It needed just a little tweaking to fit right, and after seeing the print I changed the shape of the front few inches to better match the real thing too, so the final part will look better than this first print.

Two birds, one stone...maybe...

Like many of the guns I've built so far,  CETMEs use a receiver flat that gets folded into a receiver shell.  I'm going to make my own bending jig because I can.  A problem with these flats is getting them folded straight and to the right size.  Instead of making a bending jig and a separate straightening mandrel, I'm going to try to do it all at once.  I'm going to use a 3D printed jig mostly to see how it works.  Instead of just a round rod in the center, I drew up a mandrel to match the contours of the inside of the receiver.  Hopefully it will keep things straight and symmetrical.  Since I have a large piece of G3 receiver left over, I decided to flatten it out and test my jig idea with it.  I printed out a 3" piece of jig for the test.  Here's how it looks before bending:

And after bending.  The jig pieces aren't even printed solid, it's only 8 walls and 25% infill, and it bent this chunk of receiver without breaking a sweat.  Just out of curiosity I kept pressing until I crushed the upper mandrel, and it took a lot more force to crush the jig than it did to bend the receiver chunk.  I have to do a little bit of tweaking on the mandrel shape, but so far it really shows promise.

When I tried my "crush to destruction" test, the lower jig didn't even flex.  There's a lot of contact surface area where the receiver is pushing down on it and the base is wider than the top to help keep the sides from flexing out.  The upper mandrel stayed pretty intact too, it crushed directly under where the pressure  from the press was applied.  Keep in mind that this wasn't printed solid either, just 8 walls and 25% infill too.  Here's the upper mandrel post-destructive test.  It didn't even really crack and there is no layer separation, it just kind of smooshed until the plastic tore. 

Seperation anxiety

Like many military guns of the post-war era, CETME rifles consist of a few hard parts in a sheetmetal receiver shell.  Since I need to reuse the parts, I need to liberate them from the receiver pieces included in the kit, and that's part of why I've put this project off as long as I have.  The most common method is to grind the spot welds thin then peel the sheetmetal off.  I started with the front trunion because it's the biggest/easiest piece.  I didn't even need to grind through the welds.  It looks like some of them were already broke and had been for a while, and the ones that weren't were pretty weak.  This should have been the most solidly mounted part of the whole receiver.  When you hear people say to be wary of the quality of Spanish guns, this is why...

The rest of the parts were, in fact, properly welded.  When buying the parts I needed I also bought a G3 rear receiver section to harvest the rear sight base and stock attachment weldment(though I won't be using the iron sights at all on this build it was cheaper this way).  Here are all the parts I scavenged along with what's left of the receiver pieces:

Always start with the legal stuff

As with all the other parts kits I've built, this CETME kit was once a select fire rifle.  Because of that, the first thing I'm going to do is mod the fire control group so that it will only function as a semi-auto.  The CETME fire control system is similar to, but completely different from the G3 trigger pack so no individual parts interchange.  The CETME is so close to it's G3 cousin that a whole genuine PSG-1 grip assembly would fit on this build with no fuss, but just the grip/fire control assembly alone is literally 8x the cost of the CETME parts kit.  Semi-auto G3 parts are available, but no such luck with the CETME so the original parts need to be modified.  There are several guides available on the internet, so I won't bother going through every step.  

On G3 style rifles, leaving the front grip housing pin in place makes your receiver qualify as a machine gun, so it can't used.  Conveniently, the real PSG-1 lower doesn't use the front pin either so I would have eliminated it anyway.  The first thing I did was whack the ears off the grip housing.

Then I took the whole thing apart and modified the internal parts.  Most of the pieces needed a little bit trimmed off, and the fire control cage needed a corner cut off and a shelf welded in it's place.  Here are the bits after being modified:

While I was at it, I crushed the auto-sear in my vice.  Here's what's left of the auto-sear along with all the other naughty bits that got cut off:

With all the parts trimmed, the trigger pack can go back together.  The selector is still a 3 position selector, but it now goes Semi-Safe-Semi.  Once I know everything works, I'll cold blue all the parts.

New project time: The PSG-None, a CETME based PSG-1 look-alike

This whole project is going to be an exercise in "Fake it 'till you make it."  A while ago I made a 3D printed H&K PSG-1 costume prop for a friend.   Researching for that project got me interested in the PSG-1 it's self.  It's a sharpshooter rifle based on the H&K G3 and was modified for extreme accuracy.  Real PSG-1s, if you can even find one for sale, are ridiculously expensive.  And not just "Jeff is being cheap" expensive, but "sell half your possessions" expensive.

The CETME C is on the other end of the G3 type spectrum.  It's not actually G3 based, it was the precursor of the G3 series that was designed for the Spanish army.  The G3 battle rifle is an evolution of the CETME design, and they are so similar that some parts are directly interchangeable and many more with some minor alterations.  CETME parts kits are also still dirt cheap, just about the cheapest parts kits of any type on the market, and you know I'm a sucker for cheap things.  I got mine from APEX for a whopping $125.  Here's what I'm starting with.  The parts kit is in good shape, but is definitely used.

I'm not going to call this a PSG-1 clone because it definitely isn't.  This is going to be a low buck "stand back and squint and it sort of looks right" build.  I'm not looking for ultimate accuracy either, just a good shooter.  Since even PSG-1 parts are expensive, I'm probably not going to use any, hence the name PSG-None.   It will be a mix of CETME, G3, and 3D printed Jeff made parts.  

Mr. CETME is horrified with what's about to happen...

How to put a used AR-15 sight on a new barrel

As the title says, today I'm putting a used AR-15 front sight on a new barrel for my M16A1 project.  I'm going to try to make this an actual how-to so I hope it all makes sense.  Like many other guns, M16/AR-15 front sight towers are pinned to the barrels.  The difference here is that they use tapered pins instead of straight ones.  If everything is new and undrilled, it's not so big a deal.  But this one is used and it's not something the average AR DIYer has the tools to do because the sight has the holes already, but the barrel doesn't, so just center punching and drilling isn't going to work, and the tapered pin holes make things worse.  At a minimum you need a drill press, but preferably a mill should be used.  The "easy" solution is to use something like Brownell's Retro barrel that already has the sight pinned onto it.  I, of course, always do things the hard way because as I've previously discussed, I'm stupid.  I also want to use as many of my original M16A1 parts as possible.  The barrel I'm using is a JSE 20" "lightweight" profile nitrided barrel with a 1x9 twist and a .625" gas journal for the early Colt gas block/front sight.  It's a pretty good match for the M16A1's original "pencil" profile.

The hardest part of this whole process, at least for me, was trying to figure out how to make sure the sight block was lined up with the upper receiver.  If you don't get the alignment just right and it ends up canted you may not be able to get it sighted in.  I ended up using one of my precision parallels in the rear sight channel of the upper for the back, and used the front sight ears for the front.  This isn't the best way to do this, but it's the best I could come up with without making a whole dedicated jig.  Once everything is aligned, a vice grip on the front of the gas block is enough to keep it in place as long as you don't knock it around too much.  If you're not using smooth jawed vice grips like mine, put some padding under it so that you don't mar up the finish.  Also be sure to install your barrel nut and handguard retainers before you start because you won't get another chance and your spacing will be wrong without them.  Make sure your front handguard retainer is tight against the stop or it will rattle.
*Addendum: It has been brought to my attention that I could have just boresighted it to get things lined up, and now I feel stupid(especially considering that's how I roughed in the sights after I got everything assembled).

The second hardest part of this whole thing is getting it all square in the mill so that our holes get drilled straight.  This requires a little bit of faith in Colt.  If your sight block doesn't have a sling swivel, you can use the swivel pin hole for alignment.  But if it does have the swivel riveted in like mine does, you'll have to use the gas tube pin hole.  This is where the faith come in.  I am trusting that Colt drilled all the holes in this thing parallel to each other.  As a machinist by trade, I have calibrated eyeballs so to get everything square I used a drill bit in the gas tube pin hole as an indicator and eyeballed it so that it was parallel to my mill's spindle in both X and Y.

Next up was using the centerfinder shown above to find the center of the rear pin hole.  Once found, it was time to drill.  As I mentioned in the beginning, this is a nitrided barrel which means that it's just going to laugh at regular drill bits.  Carbide drills are available, but because we're essentially drilling half a hole the bit will want to wander so they're not a great choice either.  The best choice is a carbide flat end mill.  It will cut the best without wandering.  I'm using a 1/8" end mill, which is only .005" bigger than the proper #31 drill.  This will be ok because the pins are tapered and the idea is to cut down through the barrel but stop before the end mill gets all the way through the sight block.  I don't have any pics of this, but it's just drilling a hole, nothing exciting.

After the hole is drilled, it needs to be reamed.  It needs a #2/0 tapered reamer.  As much as I hate buying single purpose tools, sometimes you just have to have the right tool for the job.  I bought one on e-bay for $8.  I was very nervous using it because it's pretty small and I didn't want to break it.

Go slow, use lots of cutting oil, clear the chips often, and check your progress frequently.  It's very easy to go too far.  Using a tap handle by hand, I went 5 turns of the handle between checkings because once it starts cutting, it cuts fast.  Making sure the hole is free of chips, you want the pin to be sticking up just shy of 3/16" when you drop it in with no pressure.

Once you get it that far you can take the assembly out of the vice and drive the pin home.  It's best to have a proper block for this, though a block of wood will work in a pinch.  I found a punch block on Thingiverse and printed it out.   If you reamed your holes right the pin should be tight when it's sticking out an even amount of both sides of the sight block.

With the rear pin in, we can leave the vice grips off and do it all again for the front pin.  Follow all the same steps as the first pin.  If you've never used this kind of centerfinder, they're very handy.  The pointy bit goes in the hole you want to locate, then you just move your X and Y around until the pointy bit is lined up with the shank.  You set it by feel, so no calibrated eyeballs required.

Once all the fun and games are done, you should have your vintage used sight properly installed on your brand new barrel. 

To be honest, this took me the better part of a day.  Lots of checking, double checking, triple checking, and checking again.  It's not particularly hard, but if you don't use jigs you really have to take your time.  *Future post spoiler alert*  So how did I do at lining things up?  Pretty good.  I had to set the rear sight about 1/3 to the right in order to get it sighted in so I didn't get it perfect, but it's more than close enough.