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.

3 comments:

  1. Trigger group from a Suomi?

    ReplyDelete
  2. Awesome! I'm gonna trade them for browser cookies I've been hearing about.

    ReplyDelete