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.

Look Ma! A 3D printed rifle!(sort of)

At long last here's how my SCR-ish rifle turned out.  Quick recap:
AR based straight pull bolt action
Bear Creek side charging upper in 7.62x39
Bear Creek 16" stainless barrel with cheap ebay muzzle brake
Gas block installed backwards to block off the gas port in the barrel
3D printed lower in eSun PLA+, stock and free float handguard in Ziro Marble PLA
AR hammer and trigger modified to work with relocated and 3D printed trigger and transfer bar
Rise Armament anti-walk pin set for the printed trigger and transfer bar (I still need one more longer screw for the trigger because the printed lower is thicker than a standard AR through the trigger pin location)

Once I get a few hundred rounds through it and am more satisfied that the lower won't crack with use, I'll probably reprint it in black.  Here's how it looks all assembled:

It's hard to believe that these are basically the same rifle:

Handguard

I got started printing the handguard for my SCR project.  It's long enough that I had to print in two pieces to fit my printer, so the nose cap locates with a half lap joint so it's easy to align.  I also had to print the hecking thing 5 times because it was storming that day and the power kept flickering and shutting off my printer.  On the plus side, I had some spares to destructively test.  It clamps onto the barrel nut using 10-32 screws, and to my surprise, the blind side of the hole broke out before the threads stripped. I also tried crushing it in my little bench vice, and it took a lot more force to crush than I anticipated.  Just like the buttstock, I could literally jump on this thing and it probably wouldn't break.

Just some tips

Just a few quick tips for today.  First, poor man's bore sighting.  I am way too cheap to buy dedicated bore sighters for my guns.  Turns out, you can buy laser modules really cheap though.  So that's what I did.  I got a few laser modules for around $2/each, then a 2xAA battery pack with switch for another $2.  Some wraps of electrical tape so that it fits snugly in the chamber, and I've got a fairly universal bore sighter for $4.  It's not as accurate as a commercial bore sighter, but it's good enough to get me on the paper.

Tip #2 is for anyone assembling an AR, or anything else that has little springs and parts for that matter.  Do as much assembly as you can inside a ziplock bag.  The Gallon and Freezer size bags will fit most ARs and pistols.  That way, when your springs go sproing, they stay contained in the bag(or at least only have one direction to fly out).

Safe-ish

I am 100% unsatisfied with the safety on my SCR rendition.  It works reliably, but I don't like how it's layed out.  When I flipped the selector lever to the other side of the receiver, I had to move the the detent and spring too.  To be honest, I just kind of made it up as I went along, and it shows.  I'm still using the original detent just with the base ground off. That bit is OK, the real problem is the spring.  I made the detent pocket as shallow as I thought I could get away with so that I had more solid plastic in the receiver, but that left me with a spring that could only be 3-4 coils long.  Additionally, to remove the selector, you have to use a punch to override the detent and knock it out.  I don't see this as a good long term solution.  I also had to notch the back side of the safety lever for the head of the screw for the Rise Armament anti-walk pins I'm using, but that's no big deal.  Here's what I've got now:

For Receiver Mk3 I've decided to add a channel for a longer detent spring.  It goes from behind the detent into the hole for the trigger pin.  This way I can use a longer spring, and can take some tension off the spring by pulling the trigger pin when I want to take it apart.  It's will be a little fiddly to assemble, but a lot of the springs on ARs are like that.  While I was revising things, I also thickened up the trigger guard a bit to make it a little tougher.

Flexin' like a ninja

Like most things on this gun, the buttpad is 3D printed.  I could have printed it in regular plastic, but where's the fun in that?  While 7.62x39 isn't exactly a stout cartridge, I decided I didn't want a hard plastic buttpad.  Instead, I used Ninjaflex TPU filament.  If you've never used Ninjaflex, the filament coming off the spool is slightly stiffer than a rubber band.  It's hard to print with, and has to be printed very slowly.  It's printed fairly course with .2mm layers, I've had mixed results printing with thinner layers.  I printed it with 4 walls and 15% infill, making it just a little bit squishier than the Limbsaver on my Mosin.  Nice and flexible:

I, of course, only have red Ninjaflex, and I didn't want it red, so I had to paint it.  Remember my love of SEM from my previous Impala posts?  Well, SEM to the rescue again.  If you're not familiar with SEM Colorcoat, it's made primarily for automotive interiors.  It's also one of the few things that works well on printed TPU.  It sticks great, and because it's made for plastic, fabric, and vinyl, it flexes without cracking.

Speeding things up a bit

When I test fired my SCR, I had a few light primer strikes.  Not completely unexpected, it's a common problem with AR platform 7.62x39 steel cased ammo like I use.  Instead of swapping to a heavier hammer spring which would increase the trigger pull, I learned that bobbing the hammer can be an effective solution too.  The lighter hammer moves faster, which imparts more energy to the firing pin, which hits the primer with more energy.  There are pages and pages of internet arguments about it, but the overall consensus is that it works.  As a bonus, it also reduces lock time, the time between when you pull the trigger and when the primer fires(although admittedly my senses aren't fine enough to ever notice).   Anyway, I got out my grinder and whacked some mass off the hammer.  I didn't go as far as some people have because it's easier to take more off later than put it back on.  If it doesn't work, I'm not out anything but a few minutes time.

The other thing I did was make a knob for the charging handle.  IMO, the handle is too short for a bolt action.  It puts my hand too close to the pic rail on top of the upper receiver and is just uncomfortable to use.  It would be fine in a standard semi-auto where you don't use it as much, but having to use it for every round just wasn't going to work for me.  I printed a fairly basic ball knob that just friction fits inside the existing handle.  It's only 5/8" longer, but it makes a world of difference in use.  It's printed solid, so I'm not worried about it breaking off.

Stocks and bonds

Since the printed grip section ended up so ridiculously strong, and the back end won't see the kind of loading that the grip section will(and since I was getting low on filament), I dropped the rear section down to 4 shells thick when I printed it.  All the other settings were the same.  I'm not the biggest guy and even with the lower shell count, it's still tough enough that I can stand on it no problem.

Since I had to make my stock in two pieces, I've got to glue it together.  As mentioned earlier, from my experience with printed prop guns and swords my preferred method for this kind of thing is to run a hardwood dowel through the parts and glue the whole thing together.  It's quick, and makes a stronger parts than it would be if it was all printed.  For this stock, I'm using one long dowel all the way through, and a short one to aid alignment.

For this kind of thing, ordinary superglue is my adhesive of choice.  My preference is Gorilla brand superglue because it tends to be a little bit thicker than other brands.  I dribble some down the dowel holes, then slide it all together.  No need to be stingy here, the more glue, the better.  Note though that if you're going to leave it as a raw print with no sanding or painting, spilled or squeezed out superglue tends to leave a white haze on the glue joint.  Since superglue sets so quickly, you'll likely only get one shot at putting things together, so be prepared.  Once glued together, I put the stock in a clamp to let it sit overnight.  Superglue is a moisture cure adhesive, so the more humid it is, and the more moisture is in the wood dowel, the faster it will set(also why it bonds skin instantly).

In an unrelated matter, I cut a piece of Harbor Freight floor mat to put in the back of the upper receiver.  Since there is nothing to stop the bolt carrier's rearward travel until it hits the lower receiver, this acts as a buffer for the bolt carrier so it doesn't smack the plastic of the receiver when you rack the bolt.  If it doesn't hold up, I'll try a different material.

In another unrelated side note, for those who are curious, my trigger breaks around 5.5-6lbs(best I can measure with my shoddy equipment), and the break is fairly clean.  Not the greatest trigger ever, but acceptable given how wonky it is.

Testing, 1, 2

I started printing my SCR stock last night, and the print failed part way through.  Looks like a nozzle clog or something, nothing major.  But it did leave me with a half printed part that I didn't have a use for, and since I'd been curious about how strong the stock would be, I decided to do some destructive testing.

This part is Ziro Marble PLA(not PLA+), printed at .16mm layers, .45mm line width, 7 shells, 15% infill, and 75% fan speed.  I clamped it in my vice, put a prybar in one of the holes, and started pulling.  While in no way was this a scientific test, my calibrated arms(from years of working on cars) tells me I was putting about 75lbs of force on it before it broke.  Most importantly, it didn't shear across the layers, it broke out jaggedly meaning I had very good layer adhesion.  Interestingly, it doesn't look like I had great bonding between the lines of print in each layer.  Regardless, I'm not going to worry about the strength of this stock anymore, it should be more than strong enough for how it will be used.

Investing in stocks

Through much trial, error, and cursing, I got a stock modeled that is reasonably comfortable without having to reach too far for the trigger.  3rd time's a charm.  I lowered the grip portion even more, and made the whole thing narrower.  It's closely patterned after a Marlin 60, which is the most comfortable rifle I have in the house at the moment.  I printed it out in Vase mode, so it's only one line thick, but it used a minimum of plastic and I'm just trying to get a feel for how it fits.

Since my print volume is limited, I can't print this all in one piece.  One of the tricks I use while 3D printing prop guns and swords is to add a tube through the middle of the parts, then once it's printed, glue in a 1/2" wood dowel rod.  This both helps align the parts, and adds a lot more strength than you'd expect.  I also added a 2nd, shorter pin hole for alignment purposes.  I haven't finished modeling the butt plate yet, but here's how the pieces look inside:

We're not the Avengers, but we can still assemble.

With my lower printed it's time to fit everything.  Everything in the CAD file is pretty much drawn to size, which means that in the physical print, everything has slightly too much material.  I'd rather have too much than not enough so I'll leave it like that, but it does mean that the lower will require a little fitting.  All the holes get cleaned up with appropriate sized dill bits, and any burrs or bumps where other parts fit need to be filed smooth.  I left the surfaces where upper sits on the lower slightly too big in the CAD so that I could get a perfect zero slop fit between the upper and lower(particularly in the buffer tower area), and that also means that there should be enough material to make it fit well with any brand of upper.  This makes it less plug and play than a standard AR lower, but the end result is a better fitting part.  I also slightly redesigned the trigger transfer lever to make it stronger as a printed part.  If it were made from metal, the original 1/4" x 1/4" size will still work fine.

With the lower assembled, I could mock up all the rest of the parts I have on hand.  I'm using a Bear Creek 16" stainless barrel, with a matching cheap e-bay muzzle brake(which may not do much, I mostly just like how it looks).  I'm using a Yankee Hill low profile gas block installed backwards so that the gas port on the barrel is covered(and the YHM was the cheapest one I could find).  A standard barrel nut holds the barrel on, and my yet to be designed handguard will clamp around it.  It will be a free floating guard, but if it seems like it needs support, I'll tap the tube hole in the gas block for a front mounting screw.  The scope is a 3x9 that my Dad had laying around, and the magazine is a 10 round AR Stoner(actually made by ASC, and reported to feed the 7.62x39 reliably).  I'm waiting on a set of screw together anti-walk pins for the trigger and transfer bar, and I still have a lot of work to do for the furniture, but it actually kind of looks like a gun now.

It is as easy as it looks, mostly.

You know, any time anybody finds out you have a 3D printer, the very first thing they almost always ask is "Have you printed a gun?"  Well, now I can actually say yes.  I mean, I've printed several TV/movie costume prop guns for friends, but never anything actually usable.  And while this isn't a complete firearm, it qualifies as such on an AR based rifle.  I got my SCR lower CAD file updated to where I wanted it, threw it in Cura, and hit print.  16 hours later, here's what I had:

I'm using eSun PLA+, and I chose grey for this project.  I will probably eventually reprint it in black after it's tested and proven, but for now the grey will show any cracks or wear very well.  I recently watched a Youtube series from CNC Kitchen where he did a bunch of tests showing how print settings can affect print strength, and I recommend that everyone who has a printer go through and watch them.  Using his videos as a guideline, I'm using .16mm layer heights, 8 walls, 99% infill, .45mm line width, and 75% fan at 220°C/60°C bed.  I almost never use a brim, but I chose to here because every now and then a completely solid(or at least 99% solid) part pull off the bed. 

It took an hour or so to get the supports off.  I'm not satisfied with how it looks.  Because of the way I had to place it diagonally on the print bed to fit my printer, there is a lot of banding in it.  Overstuffing the line width like I did (.45mm line width extruding from a .4mm nozzle) helps make the print stronger, but also exaggerates the look of the banding.  It's not the prettiest, but it should be strong and functional.

Stuff that matters

This is the part of projects like this that I like the least, modifying parts that I actually paid for.  Though I pretend to know what I'm doing, I'm pretty much making it up as I go along and I'm never certain anything is actually going to work.  With the printed stuff it doesn't really matter, cut, grind, file, and if I do it wrong I can just reprint it and I'm not really out much except time.  But now I'm to the part where if I screw something up I actually have to buy another one(and pay shipping, and wait a week).

I'm using a side charging 7.62x39 upper receiver and BCG unit from Bear Creek.  It's inexpensive, and to my untrained eye looks to be decent quality.  The problem is that the bolt carrier is too long since I don't have a buffer tube for it to slide into.  Fortunately, the tail of an AR bolt carrier doesn't really do much to stabilize the bolt, all the tight clearance sliders where it contacts the upper receiver are on the front section.  So out comes the cutoff wheel.  A few whacks and some cleanup with a flap wheel, and our bolt carrier is a much more convenient size.

While it was all apart, I did some work on the firing pin too.  Google says that 7.62x39 doesn't always fire reliably in AR platforms, especially the harder primer Russian steel cased stuff that I use.  One fix is a heavier hammer spring, but that can negatively affect trigger pull.  The other fix is to use an "enhanced" firing pin.  What's the difference between the standard and enhanced firing pin?  The stop shoulder is .010" shorter on the enhanced pin so that the firing pin protrudes just a little but further.  If you don't have any size reference, .010" is about three sheets of paper thick.  That little bit can make all the difference in the world on X39 ARs.  Enhanced firing pins are cheap, but why spend $10 when I don't have to?  The left side of the line is what we need to take off:

You don't even need any special tools to do this.  You'd think a firing pin would be too hard to file, but they aren't.  Just chuck it in a drill and have at it with a file.  It's a 5 minute process.

While I had the grinder out, I cut off the trigger bit of the front trigger.  It doesn't need to be cut all the way off, just far enough so that it doesn't hit the inside of the receiver.

Once I've verified that everything works and have uploaded my files, if you want make one yourself here's where the tail of the trigger is cut.  The angle isn't super critical and I just used some scribed lines to cut it:

At the request of a guy I know, here's what the Bear Creek side charging upper looks like and a few details.  The charging handle is .740" from the front of the bolt carrier, and it uses an ordinary 10-32 socket head screw going through the handle it's self.  I don't know if Bear Creek actually makes these uppers or not, I've seen what looks like the exact same one unbranded from several retailers.  I went with Bear Creek because I was ordering a barrel from them anyway and it saved on shipping.

Don't let your dreams be dreams!

It might not look much different, but practicaly everything from the magwell back on my SCR lower has been changed.  I lowered and reshaped the trigger guard so that the bottom is at the same level as the magwell for easier printing, I moved all the safety features from the left side to the right, and thickened up some areas for a stronger print.  I also changed everything that needed to change for the lever trigger system from my last post.

I printed out the transfer lever and trigger, and to save time and filament I only printed the back half of the lower.  I also trimmed the tail of the front trigger as necessary for the transfer lever with my dremel.  I put it all together and much to my surprise, it actually works.  Even with the printed parts, the trigger pull is short and crisp.  It's a little heavy, but not much more than the original(and definitely less than my Uzi).  Not pictured but the safety works too and is index finger selectable.  It seems to work well enough that I'm going to leave them as printed parts for now.  The only extra parts needed beyond the printed bits are a 3rd AR trigger pin, and a 1/8" pin for the transfer lever.  I don't really have a good way to capture the rear trigger pin yet though(though for as often as it will likely ever come apart, it could just press fit into the plastic receiver if I don't come up with something better).

Here's how the parts fit together when cocked(minus a little bit of wobble because the pins are just kind of sitting in the tops of the holes):

Here's about how far everything moves when it's fired.  The safety acts as an overtravel stop for the mechanism, and the original trigger spring is strong enough to reset everything when you let off the trigger.

I'm just going to lever this right here.

Here's my latest idea for my SCR trigger.  Instead of a big long extended trigger, it uses a short lever to transfer motion from the new trigger to the tail of the original one.  It uses a second AR trigger with the tail cut off, but it could probably be a printed part(I'll try it just to see).  The lever can be made from a chunk of 1/4" square stock, although it may be able to be printed too.  The original AR trigger needs some of the tail cut away for the lever but since there is no disconnector in the way that's not a problem.  Here you can see how everything sits in the cocked position:

In this system, the rear trigger only needs to move 5°-6°, pretty much the same as a standard AR trigger.  If I decide it works, I'll add more material around the lever pin so I've got a stronger print.  I'm also going to reshape and relocate the trigger guard down a bit too so the lever won't protrude into it(and it will print better with less support if the bottom of the trigger guard is inline with the bottom of the magwell). The original trigger spring should reset everything.  Here's how things move when it's fired.  It still probably isn't going to be the world's greatest trigger pull, but it might be good enough.

Stocking up.

I did some more work on my SCR stock.  Not so geometric shapes like this are hard for me to do, it's not really something Solidworks was made for and I'm learning a lot as I go.  I actually printed two more stock sections in the past few days.  I got the first one off the printer and thought "Geez, this doesn't really feel different than my first attempt."  And that's because I printed the same original test file again...oops.  So then I printed the right one.  It's much better and is a much more comfortable grip and easier/shorter trigger reach.  It still needs more work as the base of my thumb sits uncomfortably against where the main section of the stock meets the grip portion.  It's hard to show the difference, but here are the two versions together showing how much lower the grip section of the new one is.  This one is also printed in Marble filament because I think that's what I want to use for the final stock/handguard prints.  I live in WI after all, and winter is a thing we generally do pretty well.

For ease of use, I chose to dovetail the stock onto the receiver.  That should give me a nice strong connection while only needing one small bolt to hold it in place.  The dovetail also gives me a lot more solid material in the area where the lower is most likely to break in use.  If need be, I can add a hole or two in that area to JB Weld in some steel reinforcing rods too.  You can see how it slides on here:

The first of many

I got my first SCR type lower receiver printed.  This print was done quick with minimal shell thickness and infill because I'm just checking fit and function, and is in no way shootable.  I also printed out the grip chunk of the stock so that I could see how it felt in the hand.  Even though I'm never going to attempt to fire this one, for legal reasons(namely the short section of test grip), this is a pistol receiver.  After playing with it some, I've come up with a list of things to work on.  First, I'm going to flip the safety lever to the other side.  It's not thumb reachable on the left side, but is index finger reachable if the lever is on the right.  Second, the grip is way too high.  I've got average sized hands and while I can reach the trigger, it isn't really comfortable so I'm going to move the grip down and forward some.  Speaking of the trigger, it does work, but as expected the pull is very long and creepy.  I'll work on making something better for the next one.

New project time.

So I saw a picture on the internet the other day of what appeared to be a 3D printed AR-15 based bolt action rifle with a traditional rifle stock and I got inspired.  In reading some discussions about it, I became aware of the Ares/Fightlight SCR which is basically an AR platform but with a standard rifle stock and no pistol grip, and I decided I wanted one.  Actual SCR lowers though are $600+ and I'm definitely not going to spend that much.

Good thing I have a 3D printer.  I'll just make my own.  I'm not going to try to make a fully printed rifle, I'll use an off the shelf upper.  The plan so far is to make a printed lower/stock, and use an off the shelf upper receiver and BCG.  This will be a straight pull bolt action rifle, so even though it uses AR parts, I won't need a gas system or buffer tube(the buffer tube is the big one because without it I can shape the stock however I want).  Since the back of the bolt carrier doesn't do much and is in the way on a rifle like this, I'll just cut it off.  I'm going to make it in 7.62x39 because I already have plenty on hand so I'll be using an x39 sized BCG, barrel, and 10 round magazine.

In reading about it, I've learned that 3D printed ARs(and many plastic ones in general) break at the buffer tube tower.  There's a lot of load on that area because of the bolt cycling, but since this will be a bolt action instead of semi-auto I don't need a buffer at all and it just needs to be strong enough to not break if I bonk it into something.

Using a picture for reference, my new lower started as a pretty straight up copy of the SCR lower.  But it wasn't really ideal in my eyes and wasn't suitable for 3D printing.  So I started changing and modifying and tweaking things as I saw fit.  The biggest change I made, other than the whole no pistol grip thing, was to move all the fire control parts up in the receiver .200"  This allows for a shorter reach to the trigger and an overall shorter lower receiver.  You can see here where the new location is compared to the standard AR, the new parts are the darker grey:

Next up was the trigger it's self.  Obviously it has to move backwards a few inches to work with a standard rifle grip.  My temporary solution is to just make an extender sleeve for it.  This is still very much a work in progress and will probably be replaced with something better.  For the time being I'm leaving the original trigger intact, I'll cut it down when I'm satisfied with how it works.  Since this is a bolt action rifle, I don't need the disconnector so the new printed trigger extension slips right over the tail of the original one.  I'll probably eventually make something with some kind of linkage, for now this is just a "see if it works" solution.

Here's where I'm at now.  I relocated all the FCG parts, added reinforcement in some areas because this will be 3D printed, and I got started on drawing the stock.  I got rid of the bolt catch too, it's not really needed anymore and the print will be stronger without it.  The stock is dovetailed onto the lower, and will have a single attaching screw running into it.  I'm not really happy with the stock yet but it's a start.