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