Tuesday, April 19, 2011

Update on the .50 BMG

I have to admit, I've been busier than heck with school and getting things set up for the summer and fall semesters, so my builds have all suffered. I have gotten a little bit of work done on the trigger guard assembly I posted about last week, and I began construction on a new bolt body made of 1.5" OD DOM steel. I couldn't use the old bolt body, since it was constructed of aluminum. The bolt must ride over the hammer and reset it after each shot, so this would have quickly worn the aluminum down and ruined it.

 First, I finished profiling the trigger guard. I didn't take any pictures of this because I was in such a hurry to get it done I forgot my camera. However, after cutting the rest of the profile and rounding a few edges, I had a complete piece ready to mount on the .50.
This presented a new problem, as the receiver on the .50 is a piece of 2.25" OD tubing, and the top of the trigger group was flat. I didn't have 2.25" round nose endmill to cut the tubing radius, and a hole saw wasn't going to work, either. What I wound up doing was taking a piece of 2.25" solid 4140 round stock, 3/8" thick, and cutting it in half. I then milled the top flat, and centered a 1/2' endmill in the piece of stock. I then took the piece of 4140 and ground cutting edges on it. Then I heated it up until it was cherry red and I confirmed it had lost its' magnetic properties with a small magnet. Once it hit this stage, I held the heat on it for a couple minutes at approximately the same temperature. I then quenched it in oil to harden it, and once it had cooled a bit, I stuck it in my oven for 1 hour at 500 degrees. I can't say for sure how hard it is, but hitting it real good with a file did nothing but dull the file teeth. After this, I took a piece of 1/2" OD steel rod and welded it in place in the slot I had milled in the half moon shaped piece. I was able to cut a nice radius in the top of the trigger group with this on the mill. Here are some pics of the completed radius, though I could've taken better pics.

 Here's the completed cutter

Next up, I needed a way to mount the housing to the gun. I figured the easiest way to do this was with some 5/16" Allen head bolts. I didn't want the bolts to show, so I got an endmill out and countersunk the bolts into the housing. Some .5" OD cold roll steel stock, drilled and tapped to 5/16" served as nuts. The housing was mocked up in place, and the tapped pieces of steel were tacked in place very carefully.

The screws and tapped pieces of steel.

Setting up the housing to countersink the allen bolts

With everything welded in place, the trigger group was bolted on, and everything was test fit for clearance.

I have GOT to move that scope mount forward.

With that part done, I needed to machine a new bolt body that would work just like the old one, but would facilitate the use of a hammer instead of a striker. I started out with a chunk of 1.5" OD, 1" ID DOM tubing.

First, I threaded the inside to accept the old bolt head,

Then I threaded the outside so that the old 2" sleeves would thread back on.

Here's the new steel bolt body next to the old aluminum one. The one on the left is the new steel one. I haven't sanded or polished it yet, so it's still a bit rough. I also have to cut threads on the back end. I should have this done tomorrow. I hope to machine a new firing pin then as well and also mill out the bolt for the hammer to travel through and effectively whack the firing pin.

That's all for now, more tomorrow I hope.


  1. A true Engineer. Don't have the right tool? Just make your own! Fantastic. I bow to your superior redneck engineering skills my friend.

  2. Aw, shucks. *blushes*.
    Tweren't nuthin'.

    Seriously, though, I went ahead and milled some 1018 steel with that thing today. As long as I cut slow, it worked fine and was still sharp when I was done.

    I got the bolt back together and almost ready to go, I have some final milling to do on it to make it work 100%, but so far it cycles well, the hammer drops and recocks smoothly, etc. I kinda wish I had used a hammer setup to begin with. Live and learn.

  3. Oh, and a tip of the redneck's Stetson to you for your kind words, my friend.