Wednesday, December 29, 2010

More on the Bill Holmes-ish .50 B.M.G. rifle

Been a couple weeks since I updated, I know. I have been pretty busy with the Christmas holidays,  with work (had to work the holidays, I don't think there have been too many holidays I don't wind up working. All part of the job.) and family in town and a whole list of other stuff to keep up with, I just haven't had much time to sit down and type up an entry.


Well, at my last update I had a more-or-less complete receiver sitting in my garage, a bolt that had had its outer diameter turned, a fire control group, and a few other odds and ends. One thing I lacked was a buttstock of some sort. I looked at the rifle for a few days trying to figure out what would work best and look like it fit the overall rifle.

This in itself was pretty difficult, because there are a number of stocks on the market that look good on most homebuilt rifles, such as the M4 collapsible stock, or the standard A2 buttstock from  a m16 or AR15. I had a couple of each of these laying around, and held them up to the receiver for mockup, only to quickly shelve them again. The 2.25" outer diameter of the rifle just didn't look right when paired up with the roughly 1.375" outer diameter of the collapsible M4 stock, and the A2 didn't look right at all.

I went over to Google and typed in "tubegun" to see what else was popular or available so maybe I could get some ideas. I found several that made use of AR15 and M16 stocks of many different manufacture, such as some seen on this site. In fact, those stocks look great on those tube rifles, but on my large receiver, an AR stock was just absolutely goofy looking. I feel that if you are going to build a firearm, it is important to at least try to make it look proportional.With that, the AR stock idea was shelved.

I couldn't very well use the exact stock method Holmes outlines in his book, as it is nothing more than a piece of tube with a flat plate attached. It really wasn't very flattering, although I realize his idea was more to have something utilitarian than pretty. After all, the buttstock does not decide whether the gun goes bang or not. After banging my head against the wall for a few days trying to decide what to do, I finally threw something together out of a few pieces of scrap material I had laying around. With the idea that I would build something similar to what Bill Holmes designed, but with a bit more eye appeal. I started with a piece of seamless DOM tubing that was about 1.375" OD, then cut off a 10" long chunk of it and chucked it in the lathe. I then knurled the tubing in the lathe after squaring off the ends. I had a small section of 4130 2" OD round rod left, so I bored it out for the DOM tubing so the tubing would sit perfectly centered in it, then fired up the welder and burned it in place. Once that was done, I cut a plate from .375" plate in the shape of an AR buttstock so that a buttpad meant for an A2 stock would fit and look right. I drilled and tapped 5/16" holes in the 4130 round stock I had previously welded to the DOM tubing, then drilled 11/32 holes in the end of the rifle receiver to match the drilled and tapped holes in the 4130. When the button head bolts were installed to attach the stock, it pulled the whole thing in tight, and the bolt would move all the way back in the receiver and bottom out on the buttstock, providing full access to the ejection port. It came together so well, there's no way I could have ever planned it.

Still, after looking at it, I still didn't like the large tube to small tube transition, and figured if I was going to use what I had thrown together, I needed to add a little bit to it. I dug around in the scrap bin and found some .5" 1018 round steel rod. I cut a good 14" section of this off, did some simple bending on it, then welded it to the bottom of the buttplate going forward to the 4130 round stock that fit into the receiver. I took another chunk of .375" plate and cut out a rectangular section that was welded to the bottom of the 4130 piece. I welded the .5" round rod to this to complete the buttstock for the moment. I then cut a slot in the bottom of the rifle receiver directly below the buttstock mounting area for this flat plate to slide in to place. This filled in the gap behind the AR pistol grip and the round rod on the stock I made. After all that, I cut up some .125" plate to fill in the gap between the DOM and the .5" round rod that the stock was made from. Bolted it all together, bent up a piece of that .5" round rod and threaded one end to attach it to the rifle bolt as a start for a bolt handle. I managed to completely botch this piece, (the bolt handle), but left it on for the time being, mainly so I could get a feel for the way everything looked together.
I threw some rattle can black spray paint on the parts, and threw it together to see where I stood. Ignore the bolts in the rear of the receiver, I had misplaced the button head bolts I bought for this purpose.




I'm still not entirely happy with it, although I do have a couple ideas how I can make it look a little better. I am going to bore 3 sequential 1.375" holes through the .125" plate I had welded in and then I will sand all the welds and other odds and ends down. If I am still not happy with it........

To hell with it then. I will just make it a pistol. A reaaaalllly looooooong pistol.

I got a bit farther than this with the rifle build before the holidays, but have had two separate things going on to take up my time, one concerning the .50 cal rifle and the other concerning another project waiting in the wings. More on that later.

Tuesday, December 14, 2010

Laziness finally kicked in.

Okay, so I've been a little busy the last few days and haven't had time to update my work on my .50 BMG build. My significant other has had a bit of a setback in her education, and I have been dedicating most of my time to helping her out and getting her to feeling better. The ball is rolling again, although I'd swear someone stole our original rolling ball and put an egg shaped one in its place, because that little S.O.B. doesn't seem to want to roll straight.


Most or all of the photos I will be throwing up here today are of work that has already been done, i.e. I already did the work a few weeks back but didn't think to take pics at the time. Part of my problem is simple; I use my iPhone camera to take most of my pics and video, but while I am in the garage, most of the time my iPhone is hooked up to a ipod speaker dock so I have some music to work to. Given that Steve Jobs is an idiot, the iPhone is not entirely compatible with the ipod dock, so taking the phone off and putting it back on the dock in order to use the camera involves a lot of touchscreen-button pushing. This is not something I want to do while having oily and greasy hands and fingers. So, some of the more menial things simply don't get photographed. Thankfully, for things like that, there is always google images and youtube. So, if you are just that set on seeing someone use a lathe tailstock to drill out a chunk of metal, you probably won't see that here. However, feel free to go spend several mindless hours of your time on youtube or google images. I toss images up more as a guideline to what is being used and how, and then a completed product.
Another part of today's post I should mention is that most of the metal parts pictured look very dirty and have odd black spots in random places. Part of this is a result of doing metal work, (especially grinding and sanding) in a closed area. That black soot gets everywhere. Another reason is that I have sprayed the parts with a couple coats of black rattle can spraypaint.
Why would I do that?
Simple.
Just about any kind of metal you can buy will have an oxidized coat on it, if not a layer of what I refer to as "hot roll" coating*. Below this coating are usually a number of pock marks in the surface of the metal, as well as some corrosion and in really bad cases, corrosion to the point of surface pitting.
I spray black spray paint on the surface so that I know how far down I have to grind, mill, and/or sand until the surface is smooth enough it can be polished.
A lot of the metal I used to build the trigger guard and buttstock area was old scrap I had laying around, and as a result most of it is pretty pitted. There are also a number of grinding scuffs wherein I ground the welds I could get to. I will have to go back and sand these areas with block and some heavy grit paper and progressively lighter grit paper in order to flatten the whole area and get it looking right. Yes, this is a PITA. But, I want it to look good.
 So, with all that said, realize that most of what nastiness you see is there for a reason. Don't crucify me just yet.
On with the show.


I suppose it is worth mentioning that the original Holmes design uses a striker system of sorts, wherein a spring loaded firing pin is held captive by a sear when the bolt is pulled back, in lieu of a firing pin that is struck by a hammer. As such, I needed a trigger assembly that did not rely on a hammer assembly, such as that that many other .50 manufacturers use. I don't know for sure, but I think most of the .50 manufacturers on the market simply use a AR 15 grip, trigger, hammer, spring assembly, etc. Nothing wrong with that, of course, as it seems to work just fine. However, I'm building my rifle on the cheap, so I originally thought I would just machine my own trigger and sear system to save money. Well, as the title of the post says, I got lazy. Turns out I had a complete trigger assembly laying around from another project that would work just fine.


This is a part to another project I am building (soon to be posted about!). It originated in an open bolt tube gun (bonus points to anyone who can figure out what kind) and given that the open bolt system and a striker system both rely on a sear to release a spring loaded bolt or firing pin, this turned out to be an obvious, easy choice. I hated to put anything on the gun I didn't build, but the price of the metal necessary to build a completed homemade assembly was almost the same price as buying another one of these surplus trigger groups (about 10 bucks), so I just went online and ordered another open bolt trigger group. Yes, I'm lazy. So lazy I didn't want to carve out a new trigger, sear, and safety. So sue me.

So, the trigger/sear assembly was ready as soon as it shipped to my house. Without any pressure against the sear, the assembly worked very smoothly with no grit or unevenness to the overall pull. Even with pressure applied to the sear, the trigger pull is just slightly creepy with a decent break. Time will tell how it works out when the captive firing pin and spring assembly are being held by this sear. Overall, I like it, with a notable exception being the safety. Clunky and ugly are the best terms I can describe the safety with. I did, however, have to cut a screw tab off the rear of the trigger group and drill the assembly for two different pins that would secure the trigger assembly to the rifle receiver.
It should be mentioned here that I really did not care for the trigger group that the Holmes plans outline. The outlined assembly in the Holmes plans do not provide for what I consider a 100% secure sear assembly, even though I know for a fact that his provided planned assembly does work, given the number of these rifles that have already been built. The two assemblies (Bill Holmes and the open bolt SMG trigger assembly) both work the exact same way, but the SMG assembly is even simpler in design than the Holmes design and the sear seems a bit more reliable at first glance. Again, I know the Bill Holmes design works and I'm guessing works well, given the number of rifles built using that design. I just liked the simplicity of the one I used and the cost. Again, so sue me.

So, now I've got a trigger assembly. Great. I've got something I can run around the garage with and make "pew pew" noises with. This is fine, but what I really wanted is the trigger assembly mounted to a receiver (so I've got something I can shoulder and run around in my garage, pointing  and making "pew pew" noises). Albeit it wouldn't be as cool as this "pew pew".
So, I dug around in my scrap metal bin and found a two foot long section of some .125" thick 2" wide hot roll steel plate. After taking some quick measurements as to how tall I needed the strips cut in order to let the sear of the trigger group protrude into the receiver at least 3/16", I threw some black spray paint on the steel plate, used a scribe to outline the cuts needed, then took a cutoff wheel in a grinder and cut the plate out. I also added an extra 1.25" to the overall length, more on that in a second. I considered cutting four total plates to make a rectangle, then just decided to bend the metal in a small metal brake and only have one weld to make. I try to save myself a little welding and extra work when I can......

I threw the trigger group in this steel rectangle I had made and put the trigger group in place, clamped it all together, and drilled it for the pins that would hold the trigger group into the rectangle. After those were drilled, I cut a piece of 3/8" plate to weld in behind the trigger.


This plate was thick enough to mount my next example of laziness to.





I could have made a grip out of wood, but I already had one of these AR grips laying around on a Smith&Wesson M&P 15 lower I've had that is in need of an upper. Why complicate things when you're feeling unambitious?

The final product mocked together



It's a little rough right now, but a little sanding and polishing will fix that up.

Next up, I had to cut a slot in the bottom of the receiver for the sear to protrude through. This required a bit of filing and sanding to get cleaned up in preparation for the striker assembly that is forthcoming.

Annnnnnnnnd, the whole thing welded together........





Now, throw a bolt into the mix with a makeshift bolt handle.




So, the main body of the gun is together. Just need a scope mount, buttstock, firing pin, final bolt handle, and some miscellanea. Still doesn't look like much in these pics, but it gets better.

Stay tuned..........


*When you buy normal, non-alloy steel from your local steel yard, you can buy several different shapes (i.e. round rod, bar stock, plate, and sheet) in either "hot rolled" or "cold rolled". The hot roll is generally cheaper, but is not as clean and is usually not precisely sized. It is as it comes out of the steel mill, with a really nasty black oxidized coating on it. Cold roll, on the other hand, is extremely clean, has no black coating on it, and is usually within .005 of what size it should be, sometimes even closer. Cold roll costs much more than hot roll, though. Hot roll steel is simply the steel after it was pressed into a mold or poured into a mold, pressurized while still somewhat molten and allowed to cool, whereas cold roll steel is steel that was poured and allowed to cool before it was run through a series of extremely high pressure rolls or into a high pressure mold. It is formed under extreme pressure while still cold, or at least at non-molten temps. More info on this can be found here. Now, this only covers basic run-of-the-mill (no pun intended) steel, there are many kinds of steel out there beyond these.

Wednesday, December 8, 2010

Laughing is good for the soul. I hope.

Some of the kinds of tools that see a good bit of use in my tool collection are mill files. I have a good number of different files, each for a different purpose. Some are good for heavy stock removal while others are good for light feathering of material prior to sanding and polishing.

I had welded a seam on some 4130 stock earlier, and had chucked the assembly in the lathe and turned down most of the weld. I didn't want to go too far into the parent material with a grinder or the lathe bit, so I saved the last .05" or so for filing, starting with a heavy mill bastard and progressively working my way up to finer teeth grades of file before finishing with 80 grit sandpaper.

Well, I had been using my heavy mill bastard file on another project (soon to be posted about), and I thought I had left the file over on the workbench by that particular firearm project. When I shut the lathe down to find my file, it was nowhere to be found. I continued to wander around the garage in search of my tooling for almost half an hour when all of a sudden my phone began ringing. I picked it up and started conversating with a friend of mine who had some firearm related questions. After answering his initial questions, he inquired as to what I was doing at the moment.

I sat there thinking for a second trying to think of the best way to explain it to him, when I finally answered, " I'm looking for one of my tools, but all I keep getting is a 404 error: File not found."


About the same time he recovered from his laughter I found my file, laying right next to the tailstock of my lathe. Apparently I had put it there in preparation for the lathe work I had planned to do, and forgotten all about it.

Tuesday, December 7, 2010

50 cal barrel

Here's a link to an auction on Gunbroker that has a barrel identical to the one I used on my rifle.


http://www.gunbroker.com/Auction/ViewItem.aspx?Item=204292323

A little spendy, but a good place to start.

Machining the chambering area.

On to the next piece of the puzzle, the threaded chambering piece, or "barrel extension", that attaches to the barrel.

(I think Bill Holmes refers to this as the barrel extension in his book, as it is not the actual "chamber". I couldn't think of a decent term for this piece, so barrel extension is fine. Whatever.)

So, yet again I chucked up some more of the 2" diameter 4140 solid round stock and began the arduous task of parting it off in the lathe. Trust me when I say, parting off 4140 round stock with a HSS cutoff blade on an old Logan lathe is a real PITA. That took me at least a couple of hours or so.
Thankfully I have a new lathe lined up for purchase, and as soon as the money comes through in the next few weeks, I should have a much newer and larger lathe.
So, once I was done standing there and listening to the squeal of the metal being parted and the roar of the back gears on my lathe, I had a >2.5" long section of 4140 ready to be machined. When I was done parting the material, I faced off both ends of the section of solid round and began the next long task, boring the whole thing out to a 1" inner diameter.

I don't know who coined the term "boring" to describe drilling out large holes, but they were right on the money with that particular word. Geez, was that boring.

And messy. That took a lot of cutting oil for the drill bits and HSS boring bar.

I didn't bother taking any pictures of that process. A 1/8" bit to start, and slowly worked my way up to a 1" drill bit to bore through the whole thing.

 Once I was done with the drilling, I had to bore one side out to 1.3" inner diameter and 1.75" deep in preparation for threading.



Now, the inner .75" was bored out to 1.5".

Next, the outer 1" of that side was now bored to 1.3" and was then threaded to 8 t.p.i.





I cannot stress how difficult this was to do, doing a smaller bore and thread on the outside with a larger bore on the inside. It also had to be measured and cut precisely in order to get a round to chamber properly. The largest reason for the smaller threads was because the M3 barrel I bought was already threaded on the chamber area, and it had the most unconventional sized threads I have ever seen. In retrospect, I wish I had had a normal barrel blank to turn instead of the surplus M3 barrel I bought. Oh well, live and learn. It seemed to work out just fine in the end, however it took quite a while to do this.

The bored and threaded piece.



Next, this same piece was reversed in the lathe chuck and a dial indicator was used to check for runout to make sure I had faced it off properly. After I was certain it was, I removed it from the lathe and took it to the workbench for some paperwork.
Paperwork?
Yes. Paperwork.
As in, drawing a section that mated with the face of the bolt I had previously machined in my cad program, printing it out, and gluing it to the other side of the piece I had just bored and threaded.





You can see that there are inner and outer lines. I used the outer lines as a guide for a punch. The dashed lines were there to represent areas that did not need cutting.
I went back with a punch and outlined all the areas to be machined, and after that removed the paper in preparation for machining.
All the punch marks in the corners and inside edges were drilled with a 1/16" bit first before clamping the piece in the mill. I then took a 1/4" four flute endmill and trimmed the rest of the inner "ear" area out. As you might have guessed, the inner circular area was the 1" bore from earlier, so all that had to be milled out was the inner "ear" areas. These "ears" took several passes with the endmill, and when I was within .01" or so of the edge limit, I stopped milling. I then took a bastard cut file and finished the part until the bolt snugly fit into this piece.

Once the bolt fit snugly in place in this "barrel extension", I threaded the whole assembly on to the barrel.
Here's the extension in place on the end of the barrel with the tapered barrel retainer in place as well.



Now, here is the entire assembly including the bolt in place. It is a very, very snug fit.


It was a heck of a lot of work to get to this point, but it was well worth it to see that part come together.

Notice that the bolt only has the outside machined, and I will say now that there was a lot of work involved in getting that particular item drilled and bored as well.
With that out of the way, its getting late here and it's time for me to call it a night.
More later.....

Sunday, December 5, 2010

Wednesday, December 1, 2010

Receiver fun

Now that we're past the rest of the previous noise.......



On to the receiver!

Honestly, there wasn't a whole lot to the receiver. Let me begin by saying that the overall length is arbitrary, well, as long as it isn't any shorter than say, two feet long or so. Any shorter than that, and I would be concerned about having the muzzle blast a bit too close for comfort.

The Bill Holmes guide calls for a three foot long piece of 4130, 2.25" outer diameter and .12" wall thickness. This gives a .005 inner clearance when a 2.000" inch piece of 4140 is used for the bolt, which has shown to be more than sufficient for clearance. The bolt will move back and forth and turn freely, especially when given a little bit of oil to lube things up a bit.

Anyway, I originally bought a 3' section of 4130 for the receiver. I had no issue with a 3' long receiver at first, until I realized I really didn't like the overall look of the gun as the original plans outlined. I finally got around to photoshopping the whole thing and then I realized I preferred the receiver right around 28" long. So, back in the lathe the whole assembly went, and I parted off about 8 inches of receiver. I did a rough reassembly of the barrel and receiver blank tube and decided I was pretty happy with the overall length and appearance of it.

In the original plans, Bill Holmes outlines a number of slots that are to be cut into the end of the receiver, mainly for looks. I liked the slotted look on his receiver, but affixing a large (2.25" od) tube into my milling machine is a bit of a pain, as I don't have a vise that can effectively grip a tube of that diameter. I can do it, but it takes a heck of a lot more work than I was interested in doing, given that the whole slotting thing is arbitrary, and really is done just for looks. After mulling the whole thing over, I decided to just drill a series of holes in a similar manner as the slots were supposed to be milled.

I took the original drawing from the Holmes manual and got the necessary dimensions from it, then opened up my copy of Deltacad (my favorite CAD system) and redrew the whole receiver and measured out the series of sequential holes that I wanted. I first inserted the .5" holes in the drawing where I wanted them after calculating the given distances to make sure everything was even and equidistant, then I put a smaller circle inside the center of the .5" hole so that I would have a place to center a punch.
After that, I measured and illustrated in my CAD drawing where the slots for the bolt handle and the bolt access needed to be. I also made a set of marks in these, as I didn't want square corners to all the slots I had to cut, I wanted radiused corners instead. So, I guesstimated what radius  I wanted and from there marked the center of that so I could drill a hole and complete the inside of that corner.

Once I had all that done, I printed the whole thing out at a 1:1 scale, which gave me about 4-8x11 sheets to join together on the receiver. I then took the receiver and sprayed 3M spray-on adhesive on the receiver and on the printed out drawings. Here I made a mistake, although not a crucial one. When I applied the drawings to the receiver, I managed to misalign the ones with the series of holes to drill. I didn't notice this until after I had drilled them. Dammit.
Thankfully it isn't off by much, and it really doesn't make much difference. Thankfully it is not altogether too noticeable, but I know it's there, and it irritates me when I pick up the rifle and see it.

Once the template was in place, I got a punch out and marked the center of all the holes to be drilled, both the series of sequential holes (speed holes, as Homer Simpson calls 'em), as well as the holes in the slotted areas' corners.

Next came the fun part. Drilling a LOT of holes.
By the way, Harbor Freight is good for a handful of things, including cheap prices on 10 packs of HSS drill bits. I picked up 2 packs of 1/16", 1/8", and 1/4" drill bits in anticipation of this process. Glad I did, because HSS drill bits do NOT last long against 4130 tubing, even with ample cutting oil.
I started out by clamping the tubing to the mill/drill table and making sure it was centered for the drill bit. (Side note here: clamping the tubing to the table in preparation for drilling is not hard. Getting it clamped to the table or the vise securely enough to be milled is something else entirely.) I have a few different centering drill bits that are normally used in a lathe to drill a centered hole in stock that is to be mounted between centers and turned. I used one of these bits to do the initial drilling to mark the hole, then switched to 1/8" bits to finish the hole boring. Once that was done, I switched to a 1/4" bit to enlarge the hole, then a 1/2" bit to finish the job. I have a small carbide tool that is used for cutting and clearing any shavings that remain from drilling holes in metal, so once everything was drilled I went ahead and trimmed out any remaining shavings.

This is what I was left with



And, after adding a barrel and barrel nut for mockup,



I also drilled holes about 3" in front of the chamber area in which the tapered barrel retainer would reside. Twelve 5/8" holes were drilled in two rows of six holes around the circumference of the receiver. The tapered barrel retainer would be plug welded through these holes once the chamber and a handful of other things were machined and set in place. However, that is for another entry......