What grade is this bolt?

Last time I posted about the Uzi, I started machining the bolt.  In what I'm sure will be a shocking surprise, in this post I'll finish it.  I got all the sides machined last time, all that's left are the ends, and just like a loaf of bread, the ends are the worse parts.

This operation to finish the back side of the bolt is one of the most nerve wracking things I've done in a long time.  All there is to it is a little bit of 3D machining, and drilling three holes.  Why was so nerve wracking?  Because the hole for the recoil spring is nearly 6" deep, through moderately hard steel, with a less than ideal coolant situation.  After more painfully slow machining/drilling with very small pecks and full retractions between pecks, it was done.  The Z axis got a workout that day, I tell you what.

With that done, there was only one operation left, but it was the most critical.  The Uzi being what it is and working the way it does, it generally doesn't require much precision.  This last operation is the only one that that really matters and it has to be exactly right.  Trimming the front end of the bolt and machining the bolt face is what will set the headspace for the gun.  Without having the headspace right, the cartridge case could rupture and the gun blow up.  It's not quite as critical with a blowback as it is with a locked breech system, but still important.  Finish drilling the recoil spring hole was no biggie but of all the painfully slow machining I've done, what's next was the slowest.  I wanted to avoid chatter in the cartridge recess/bolt face as much as possible.  To finish machine the bolt face, I had to use a 5/16" cutter hanging out of the collet 4", spinning at just a few hundred RPM, and stepping down a whole .010" at a time.  Then I had to drill the hole for the firing pin tip, and my long collet only cleared the side of the bolt by .020".  Know what's fun?  None of that.  But it worked and got the job done.

I actually did one last manual operation once the CNC work was done.  I located and drilled the through hole for the extractor retainer pin on the mill by hand.  It crosses the extractor hole off center and to drill it first might have made the extractor drill bit wander.  All in all, I think it turned out alright.  For something I reverse engineered with a calipers and machined in a tough material that I'm not very familiar with, I'm satisfied with the results.  Here it is next to my original IMI bolt:

It's fun to play dress up

I keep looking at the original Vietnam era Colt M16A1 parts kits, but they're always really beat and a lot of money for what you get.  I mean, you can get a whole, complete, new AR-15 for what an M16 parts kit costs.  Even cheaper than that though is my EBR, a Mossberg 715T.  The 715T is already just a 22lr dressed up in an AR-15 shaped plastic shell, and I decided to dress it up even more.

The 715T being just a 22 in a plastic shell that it is, standard AR/M16/M4 pattern parts won't fit.  In keeping with my general theme of "lets see how cheap we can do this," I decided to use airsoft parts with 3D printed adapters.  Some airsoft parts are surprisingly high quality, those guys get as into their hobby as we get into ours.  For my dress up kit I'm using an ICS stock, but just about any airsoft M16A1 style stock should work as long as it's the style with a the long screw attaching it. For the front end I'm using a JG/Golden Eagle M16A1 handguard. The whole conversion only cost me about $40 for the parts.

Here are all the printed parts that are needed:

And here's where they go on the rifle:

The handguard adapter holes are sized to be tapped for 8-32 socket head screws. The stock adapter hole is sized to use a 10-24 screw. I didn't have the long original screw for the stock so I made one with some 10-24 all-thread and welded a screw to the end to hold the stock on. It ended up being around 10" long, basically all the way from the butt plate to the 3D printed adapter.  The front handguard cap gets screwed to the front sight post with an 8-32 screw, and the front of the handguard needs to be trimmed slightly for screw clearance like so:

The front sight post and handguard cap should be a tight slip fit over the barrel, and the original 715T sling swivel will still work. I use an optic anyway, so the front sight is just decoration for me and a little bit of movement is ok, but it you use iron sights the front sight post has two holes in the bottom for 4-40 set screws if you really want to lock it down.  Some versions of the 715T have a threaded barrel so an actual flash hider can be bought cheap and threaded on, but mine is unthreaded.  My flash hider is printed solid and is meant to be a tight press fit onto the barrel.  It took a lot of force to to get mine pressed on, and it should be more than enough for a 22lr.  It's also pretty much just for decoration anyway.  The handguards need to be glued to the two handguard adapters too.  I used hot glue, but superglue would work just fine too.

When everything is printed in black and assembled, here's what we end up with:

If you happen to have one of these rifles and want to dress it up, my printable files can be found here: https://www.thingiverse.com/thing:3610994

I hate machining steel.

Now for the hardest part of my "doing it the hard way" Uzi project, the bolt.  There are a lot of differences between semi-auto and full auto Uzi bolts, primarily because of the striker instead of the fixed firing pin.  I could have bought a factory semi-auto bolt, or I could have modified my original bolt, but as previously discussed, I'm an idiot and apparently a glutton for punishment.  I decided to just make my own.

I made a CAD model of my FA Uzi bolt, then added the necessary modifications for semi-auto use so that I could CNC machine it.  The factory Uzi bolt is 4130 steel, but I decided to make mine out of A2 tool steel.  I chose A2 because it machines alright, it's very tough without being too brittle, and most importantly, I have a large chunk of it.

I hate machining steel.  Nothing about it is any fun.  It's hard on cutters, it's painfully slow compared to aluminum, and the chips are tiny little razors just waiting to bury themselves in your skin.  I'm also used to machining aluminum but very little steel(and even less hardened steel) so I run steel very conservatively.  My little CNC mill is not fast, and it is not powerful, I could never run aluminum at the speeds I'm used to.  But for steel, I don't need high speed anyway so it works out alright.  I use carbide endmills for everything because life is too short for high speed steel, and even good carbide is cheap these days.  Also machining high speed steel with high speed steel cutters is likely just going to chew up cutters so carbide is cheaper in the long run.

My new bolt is going to take 5 setups to machine, basically machine a side, turn it in the vice, machine the next side, and so on.  I don't need to machine the top because it's already flat.  After several hours of painfully slow machining, it's starting to look like something.

Operation 1, the right side:

Operation 2, the bottom:

Operation 3, the left side:

The last two ops are the important ones, and also the most nerve wracking, so stay tuned.  Same Bat time, same Bat channel!

More spoilers

Another post full of spoilers.  First, I have a 3D printer(two actually, but who's counting).  Not really that big a deal, lots of people have them.  Second, I have a 3D scanner.  It is not the world's greatest scanner, but it works for my needs.  And what I needs now are some grips for my Uzi.

I was not happy with the grips that came with my parts kit.  The pistol grips were ok-ish, but the foregrips were just beat to death.  Scuffed and scraped with half the ribs worn off.  I definitely needed something better.  I bought some original "Excellent condition" grips from a vendor and they were better, but definitely still used.

I decided that I wanted to 3D print some new grips, but there is only one CAD file that I could find that was even remotely accurate looking, and it's proportions were so far off that the parts could not be made to fit the real gun.  And that's where the 3D scanner comes in.  Usually I scan people to 3D print mini versions of them so my scanner isn't great with small objects, but it's good enough for my needs.  The actual scanning doesn't take long at all, but there is a lot of post process clean up with involved.  To be honest, it probably would have been faster for me to just redraw them in Solidworks, but this whole project has been an exercise in doing things the hard way.

Anyway, here's what I ended up with.  I printed them in blue because only the cool kids have blue handguards.  Deal with it.  Actually, these are essentially my "rough draft" prints and blue is what happened to be in the printer at the moment.

Overall they fit ok, but not quite perfect, so I'm going to do some more editing of the STLs before reprinting them in black.  I'm not quite happy with the texture on some of the ribs either, so I'll fix that while I'm at it too.  And, not that I'm counting because it doesn't matter for a pistol build, these handguards would count as a US part for 922r.

More legal requirements and stuff

Since my Uzi build started with a machine gun parts kit, the fire control group has some naughty bits in it that are definitely not legal for use.  We'll need to modify the lower grip assembly so that it's both legal, and usable with the striker fired semi-auto bolt.  The first thing to do is to make sure that the selector lever can't slide far enough forward into the full auto position.  That's pretty easy to do, all you need to do is weld a blocking plate into the grip assembly to limit the selector lever's travel.  I made mine out of some 1/8" steel plate and welded it in.  You can see here the plate welded in so that the selector lever can't go any further forward.

Next up is the sear.  Aside from the FA sear being a naughty bit, it won't work with the striker setup anyway.  It's not shaped right to catch the striker.  There are semi-auto sears available, but I'm cheap and it's very easy to modify the original.  Using a cutoff wheel in my Dremel, I started cutting away at the sear.  The left ear is the only one that matters because it's the one that catches the striker, but I trimmed them both, for good measure.  Here it is with the first ear trimmed:

And with the second ear trimmed:

I eyeballed the angle based on pictures of the commercially available sears.  It's not ultra critical on these things, as long as it's close enough so that the striker can't slip past the sear.  You can see here on the right side of the pic how the modified sear catches on the striker:

I wanted to check my sear engagement on the striker, so I got out my handy Sharpie and colored the sear ears.  Then after assembling things and dry firing it several times, I pulled it back apart to check the wear pattern.  Here's how much actual contact I'm getting between the sear and striker(on the left ear).  Not a lot, but enough.  More contact will lead to trigger creep, and after everything is together and working, I'll see what I can do to improve trigger feel.

That should about cover it

In my last post I mentioned the top cover of the Uzi.  Like many of the other parts, it needs to be modified for semi-auto use too.  It's got this nifty ratchet mechanism on the charging handle to hold the bolt open.  An added safety precaution on an open bolt machine gun, and just a handy feature to have on a closed bolt semi-auto.  The problem is that the semi bolt doesn't move back as far as the FA bolt, so the original charging handle ratchet can't go back far enough to unlock and slide back forwards.  The ratchet unlocking mechanism is super simple, and activates when the spring inside hits the back of the slot.  A lot of people simply take the ratchet mechanism out for their conversions, but I like it.  All that's needed to modify it for semi-auto use is to make the slot shorter to match the shorter travel of the bolt.  Conveniently, the top cover sheetmetal is the same thickness as the receiver, so I cut a leftover piece of receiver to fit the slot.  For my conversion, I needed to add a piece .825" long.  Your results may vary, but it should be around there someplace.

Uzi build, part??

I finally got the receiver of my Uzi finished.  The biggest part left was welding on the rear most section.  Conveniently, the top cover works as the perfect gauge to set the overall length.  Using the top cover as a guide (and taking weld shrinkage into account), once it was tacked in place I clamped my copper plates inside and welded away.  Here's what I ended up with:

The last little bit left was to rivet the ejector in.  I actually bought the proper rivet and used a few of the rivet bucks I made for my AK build to set it.

Apparently, I tried too hard when I set the rivet, because the base of the ejector cracked.  Oops...  It fits into the receiver snug and it's good and tight so I think it will still work.  If it ever does start to work loose, I'll get a new one.