Thursday, March 22, 2012

Project digressions

I've been working so much on the Hi Point drum over the last several weeks that I have gotten slightly burned out on it. I cut out all the parts to make a new mag tower and have it all sitting here, ready to weld up, but just couldn't bring myself to start on it at the moment. I figured that since I've spent so much time and money on it, I needed to just step away from it for a week or two and collect my thoughts on the rest of it. I still have some friction issues to sort out even if the newly angled mag tower solves the nose diving issue, and I need a clear head before I try to solve that issue. So, I dug into my project bin and pulled out some parts for one of the other builds I've wanted to start.
Don't think that I've given up on the drum, I'm just stepping away for a week or so to take a break from the usual "one step forward, two steps back" conundrum that the drum project seems to have. I'll pick up on the drum next week or the week after. All the parts are sitting here, and I want to make sure I give it 100% when I do get to working on it.
Anyway, on to the project.
I have a good gunny friend who was lamenting to me one day how there just isn't a viable option for guys like him who would prefer to have a carbine in .45acp. He picked up a Hi Point carbine in .45 at my recommendation, and although it is a viable option, the low magazine capacity and aesthetics of the rifle just don't suit him. He carried a M4 in Iraq, but hated the 5.56 round. He kept telling me how he would have given ten of those rifles for just one in .45 acp. After listening to his laundry list of complaints, I looked into the market of what is available for shooting .45 out of an AR15. It seems that while there are a handful of companies that now make a dedicated .45 AR, none are affordable and many are very hard to get. For years, Olympic was the only company that made one, and they were very hard to find and expensive when you could find them. The available mags for them were also a disappointment. In the market now, there are some who offer a dedicated lower that uses Grease Gun 30 round surplus magazines in conjunction with a .45 upper, but are still expensive, not to mention the user loses the option of swapping to a different caliber upper receiver. There is also the option of a blowback action versus direct impingement, but I was only able to find one company that has a production level upper that uses the DI gas system, and it was prohibitively expensive.After all my internet digging, I finally started to see where my gunny friend was coming from; there is a heck of a market out there for a .45 carbine that is affordable and readily available. I can't do anything about availability to the general market, but I can sure help this guy out. I figure it's the least I can do in thanking him for his service in the Marines......

To start, I procured a barrel blank from Green Mountain Barrel in with a .45 caliber bore. It was just a 16" length barrel, making it perfect for this project. I then bought a upper receiver forged blank from DSA, and some steel stock from Speedy metals. Some of this project will be outlined in this post, and the rest will be in another post to come.

To start, the upper receiver blank is literally a 0% blank, there is no machine work done to the blank at all. There are forging seams all over the receiver and the blank is oversize due to the forging process and must be machined to size. This is a problem when it comes to machining, as there aren't any good places to reference a flat surface. With no good flat surfaces, it can't be clamped easily to machine the necessary surfaces to size. Once either the top or bottom is perfectly flat, the rest of the receiver can be easily machined. After some head scratching, I finally figured out how to clamp the receiver to start milling it down. I had to extend the width of the jaws on my mill so the take-down lugs could be secured, and since the lugs are not flat, I had to make some shims that would allow me to get the receiver as flat as possible. Setting this up took several hours to get the upper with less than .001" of slope, they are just that deformed when in the raw stage.

To start, the receiver was clamped in place, and very light (.001") passes were made across the top of the receiver until a perfectly flat reference surface was registered.



Next, a dovetail cutter was used to cut the 30 degree/60 degree cuts for the picatinny rail. This was done in light passes (.005" per pass) until it met the measurements I found over at Biggerhammers site. I forgot to take pics of this, but the end result is shown below.

Here I tossed a cheap optic on the rail to check for parallel cuts from one side of the receiver to the other. The optic does not sit level front to back because....



......the receiver needed to be referenced and have the slots cut for optic retaining screws! I did this with a .1875" end mill and spaced the cuts out .1875 between slots, each slot cut to a depth of .12"

The end result is an optic that sets perfectly in line on the receiver. I also had to mill the rear of the receiver flat and file/sand the radius on the rear of the receiver to match the curve on a lower AR receiver. After milling these slots, I flipped the receiver over in the mill vise and milled the take-down lugs and bottom of the receiver to spec. Once that top rail was milled flat, I had a good reference surface for cutting everything else.
 Fits good, looks good.
I took such care to make sure everything was machined right, and the end result is that the upper and lower mesh very well. I can't even fit a .001" feeler gauge between the receivers. If you've inspected most production receivers, you might have noticed some slop between the two. One of the complaints my Marine friend had with the service issued M4s they had was slop in fitment, so I wanted this to be good enough a Devil Dog would be proud to hump some miles with it.

You may notice the odd shape on the rear of the receiver; that is where the forward assist would normally go. I am removing that from the receiver altogether, but needed the flat surface for clamping. It will eventually be milled/filed/sanded flat to match the rest of the receiver.


So, the receiver was good to go on the outside machining, but I had one big problem remaining- there was no hole through the center for a bolt or barrel. I chucked the receiver in the 4 jaw chuck on the lathe and got the nose of the receiver dialed in as close as I could get it to center. Best I could get it was about .001" total runout, which is more than good enough.

Start out with a 12" long aircraft drill, 1/8" diameter, and take small pecks until the whole receiver is bored through, then work up to a 1/2" aircraft drill and finish boring it out.


 Step up to a 3/4" drill and keep drilling. Take light cuts to keep it from going off-center.....
 Then remove the receiver and check the rear for concentric bore, before chucking it back up reversed and boring the rear to 3/4".


Clamp the upper in place on the lower and check for bore concentricity with the lower....

Since I will be boring the main receiver out to 1", I wanted the nose to be bored to .745" so I could press in the barrel. This worked out fine with the drill bit I used to bore the nose.


Here is the bottom side of the receiver after milling and boring.


The rough drilled inside of the receiver. I will eventually drill this to .875 and then get a reamer to ream it out to 1.00" so it's nice and smooth.

Here's the nose after being filed and sanded smooth....

The fallout from all that drilling on the lathe........



Next up was the barrel. I put the barrel between centers and measured runout; there was about .010" of runout from the factory. No problem, I just turned the barrel between centers until it was bore-centric. After that was done and the barrel had less than .001" of runout over the length of the barrel, I chucked up one end in the 3 jaw chuck and started profiling the barrel. Here you can see the area I was turning down to be press fit in the nose of the receiver.


After profiling the rest of the barrel down to a 1.00" outer diameter and turning down the shank to .750" for a tight fit in the receiver nose, I popped the barrel in place for a quick teaser picture....


This has been a lot of work to get to this point, so far I have a couple of days of machine time just in the upper receiver and only a couple hours of work in the barrel. For anyone considering building one of these forged uppers, I hope you like hard work unless you have a CNC machine. They are currently about 28 bucks each and a 100% complete stripped upper receiver goes for about 60 bucks. I don't mind the hard work involved because I wanted it to lock up tight to a standard lower, and truthfully it would've been a small challenge to adapt a pre-machined upper to what I wanted to do with it. If you don't have a mill and a lathe and a lot of time on your hands, just buy a 100% upper and fit a barrel to it.

There's more to this project, in fact a whole lot more. I still have to machine a bolt/ejector/extractor, thread the end of the barrel, machine the barrel retaining nut, and make the forearm, among several other things. There is also the issue of magazines, since standard Thompson and Grease Gun magazines are too wide to work with a standard lower magwell. I'll get to that soon, but for now......

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