Tuesday, June 14, 2011

Bill Holmes .50 BMG rifle update

Well, I disassembled the whole rifle to check for any damage/s. I had to clean it a lot more than I thought I would, that surplus ammo shoots DIRTY. No big deal, some rubbing and some CLP cleaned everything right up. In my visual inspection, I was looking for any cracks, abnormal rubbing, fractures, pits, and anything else that might cause a catastrophic failure later on.

So far, I have found exactly no damage, no fractures, no evidence of wear at all aside from being really dirty. Now, I did find a few issues I will have to address before finishing everything in Duracoat.

1. The bolt face needs polishing. There are still some tool marks on it from the milling and turning. These are mainly cosmetic, but there is one small area of metal where the cartridge sits on the bolt face that is about 0.001" higher than the surrounding metal, so when the cartridge goes off, it stamps an impression in the head of the case this small amount and makes it slightly difficult to remove. A small needle file and some emery cloth will remove this and polish it up smooth.

2. I will have to put in a firing pin return spring of some sort. I had trouble removing fired cases because of the previously mentioned tooling mark on the bolt face, but also because the firing pin sticks forward and won't easily retract, probably due to the gunk the surplus ammo leaves behind.

3. The firing pin now sticks out too far. In my efforts to get it to protrude enough to activate those hard surplus primers, I drilled the bolt head too deep for the pin. Now, the firing pin actually punctures the primers. This lets a bunch of hot burning gunk into the bolt head, which is part of why the firing pin sticks. Thankfully, since I drilled the bolt head too far, all I have to do is put in a small section of a spring coil to get the pin to retract. This should fit in nicely where the bolt head was counter-bored for the AR15 firing pin. No fuss, no muss.

4. The small allen head bolts that hold the bolt head to the bolt body did back out and made the bolt a little wobbly. Some locktite will easily fix this once the bolt is ready for final assembly after Duracoat. Given the epic shock I subjected them to today, I'm not surprised.

5. The barrel extension backed off of the barrel a smidgen. I forgot to torque it down before installing it the last time I had the barrel assembly out. This is not too big a deal, but it could have been a big problem had it gotten much worse, as that is what controls how the cartridge headspaces. I will likely integrate a small setscrew into the assembly and silver solder the barrel to the barrel extension after torquing it all down in a vise. All I need is a small "check" assembly that will prevent the barrel extension from easily rotating. This issue could have been prevented by me not having a case of temporary rectal-cranial-inversion, but I'm glad to see that even though it did loosen, the rifle did not blow up, and the threads on the barrel and barrel extension held together just fine.

6. I managed to scratch and ding the heck out of the stock and receiver today. I have a lot of sanding and polishing in my future anyway, so no real loss there....

7. The muzzle brake worked very well, despite not being fully ported. I meant to mill rotated ports in it similar to the last brake, but was on a bit of a time crunch, so I just bored 7/16" holes down it's length, spaced .75" apart, center to center. It vented the expanding gases to the left and right of the shooter quite nicely, as my stepson can attest to, given that he was filming to the left of the gun about 15 feet or so away and still got knocked back by the muzzle blast. However, I think it can work better, and I want to play with the design a little in my 3d modeling program a little more. This is the same program I have been using to design the silencer I plan to build once my form 1 comes back from the ATF.

8. I need more ammo. Shooting this thing is a.d.d.i.c.t.i.v.e.

It is unlike anything I've shot before, and is an absolute adrenaline rush. You start squeezing the trigger, and just as soon as you realize the trigger completed its' break, you feel the WHAM as the rifle shoves you back, (no kick, just a nice shove), you hear a decent BOOM, then the shockwave of the round exiting the barrel hits you. You can feel it for minutes afterwards. It is also very loud. The first time we had the rifle clamped to the ammo crate and fired a round off, I said, "Hmm. That's not too loud, although it does have a bit of a blast to it. That can't be much louder or have much more recoil than a Mosin Nagant or a M1 Garand." I decided to shoot my M1 Garand real quick, just to see.
Yeah.
I was wrong about that, too.
The M1 Garand sounds and feels like a .22 by comparison. My sporterized M44 Nagant is a kitten next to the .50. I imagine if I got around to building that muzzle brake for my M44 that it would have a lot less recoil than it does. Food for thought.

So, now I get to attend to a very small checklist of piddly things, as well as finish the scope mounts and bipod before I sandblast the whole thing and apply some shiny to it thanks to the good folks at Lauer Weaponry.

For now, I'm going back to my 3d modeling program and do some fluid dynamics calculations to see what I can get out of that muzzle brake. I hope y'all have enjoyed everything thus far, I know I have.

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