Anyone here know exactly how a bcg is machined/fabricated? Specifically referring to the carrier itself, and how it is made/machined? The main point for asking, is that I would like to know what is the cause for some carriers developing that rough, textured finish, sometimes referred to as “orange peel”/etc ??? I’m trying to get a better understanding of what causes this “orange peel” finish, and why some carriers from the same manufacturer wind up with this characteristic, but others do not???
Further, can anyone here comment on the bcg finishing process? Just referring to the standard finish as seen on Colt/etc. Not referring to any specialized coatings such as Failzero/etc. Are standard bcg’s just parkerized??
Thanks for any insight.
I don’t know how they do it for production, but if I were to make one I would throw a piece of round stock in a lathe, turn it down to size, drill thru the part, then cut to proper depth and diameter for the bolt. Swap it around and then cut to proper depth and diameter for the back end. Next I would load it into a mill and machine out all the other features, as well as drill the holes, tap the ones for the gas key. Then heat treat, chrome line, phosphate/ parkerized.
Then again, maybe there are manufacturing processes that I don’t know about that would be faster, better, cheaper than above.
I totally agree. The lathe seems like the only feasible method, or , if in a mass production situation, a cnc lathe. However, the orange peel texture as seen on many carriers cannot be explained, unless it is merely in the parkerizing, which to me seems unlikely as I’ve seen carriers with orange peel textures seemingly so thick, it just doesn’t seem possible to be strictly a parkerizing flaw. It just looks as if its textured down in the steel itself…???
Can parkerizing cause such rough, orange peel like texture???
Could someone post a pic of this “orange peel”? I am a machinist by trade and might be be able to give an explination.
cant help but here is a pic posted by Brownells on Facebook a couple of days ago…
seem like the front portion of the carrier has a rough finish since the early stage (2nd pic from the right) of the mfg process
I know what you’re referring to with the “orange peel” surface texture, and it appears to only be on the forward section of the carrier exterior. I figured that was from shot-peening. I know that bolts are shot-peened, but didn’t think it was really necessary for carriers. However, I’m not sure what else to attribute that surface texture to.
You are referring to the area on the left side, front between the raised pads the carrier rides on? This is cut with a form tool, while the rear is turned.
With modern cnc machining is there a reason the the bolt carrier cannot be made as a monolith unit to include the gas key? Is it cost? Does someone currently make such a unit? Or does having a monolithiic bolt carrier complicate clearing certain malfunctions?
I don’t think it would be possible, what with the gas key covering up the pocket that the cam pin rests in not to mention the actual tunnel for the gas down thru the gas key, no way to machine that.
I mean there are ways, laser sintering or using another method, I forget the name of it but it involves using weight and acoustics to weld very thin layers of metal together, slowly building the part up.
However I don’t believe either method would create a strong enough product to use as a BCG and would be extremely way too cost prohibitive.
it is most likely chatter during the manufacturing prosess. either a dull tool, poor operator, which this is no shortage of, or a warn out machine. all these things are caused, usually, by trying to get the most production possible. unless it is on a critical surface, i doubt it would make any difference other than cosmetic.
Not hard at all- Bore a hole from the bottom up, bore a second hole from the key face to meet it, Extrude Hone to smooth if needed
Thanks for posting that Brownells pic, I too have a pic, a much better pic, way more detail, but this phone will not let me post pics to the net. I can email anyone who is willing to accept the pic. My direct email is pc197933@gmail.com
ToddK, by “form tool”, do you mean as done on a shaper???
What I was referring to machining the whole BCG as one piece, without changing any dimensions of the BCG, you simply cannot machine the gas path with the carrier being one piece without boring a hole thru the bottom of the carrier which would change the whole dynamics, I’m guessing that it would prevent the gun from operating, giving the gases another route to escape from the carrier before it has the chance to do its job. I mean you could then weld a plug back in but that’s pointless.
Machining the gas key separately is easy, doing it as one piece with the rest of the carrier, not so much.
I’ve almost wondered if some carriers are cast?? I’ve got a couple of new LMT enhanced carriers with a slightly rough looking surface. The contact areas on the carrier have a rough look to them, which looks like more than just the little you can get from parkerizing. For most of my carriers the spots that contact inside the upper are very smooth, but not these LMT’s. They seem “bumpy”.
I have gotten a couple carriers like that with the rough finish and is why I polish the guide rails on all my carriers to glass smooth.
The point is, if somebody really wanted to make a carrier with an integral gas key, we have the technology to do so. Production would likely be more complicated and more expensive but wouldn’t require anything exotic
Michael, so you are polishing the top and bottom guide rails? What’s your method for polishing these surfaces? I’ve got a couple ideas myself. Curious as to what your method is? We love tinkering in the machine/armorer shop.
I just use a popsicle stick with some 2000 grit paper and go slow. nothing fancy and puts a gentle radius on the edges too. I have noticed that it cycles smoother by hand afterwards. I am sure that it would probably do the same after lots of rounds but i also feel it might save some wear and tear on the receiver as well.