I received a request to turn the rear of a “mil spec” bolt carrier down in a lathe to convert it into a pistol bolt carrier. I’ve never tried any machine work on an M16/AR15 bolt and was wondering if anyone here has any experience doing it. I’m sure that carbide lathe tooling will be necessary. Are they carburized or through hardened steel?
I told the customer that they would need to provide a print or a sample of a pistol carrier that I can measure. Please let me know if it is feasible or if you you have any suggestions, even if it is “Hell no, don’t do it!”
A “mil-spec” carrier is through hardened and carbide is a must. That being said, I’m confused. I wouldn’t think there is anything you can do to a carrier on a lathe except except turn down its diameter. Given my understanding of a pistol carrier, conversion of a standard carrier would be done on a vertical mill. Given your reputation and the quality of your work, this project isn’t worth it. I’m guessing a finished carrier can be purchased for an amount equal to an hour and half of your your shop rate. AR-15 pistols are crapastic little toys that rarely run correctly and beat them selves to death when they do. What would you say to the same guy who asked you to accurize his Llama 1911? Not a project I would stamp my name on…
I think this would be about shortening it at the back, right? I’d do it with a cutoff wheel on the surface grinder but a chop saw would do as well, then square it up with a carbide end mill.
Thanks Ned - I haven’t seen it yet but yes, he said that shortening the rear of it was most of the work. I’m not sure if there needs to be any other type of modification at the rear to interface with the buffer & spring or not. I have zero experience with AR pistols so I told him that I’d need a sample carrier or a print.
MarkG - you may be right. It sounded like an interesting challenge so I told him that I’d take a look at it. I may do the machine work but won’t be building the gun or trying to make it run.
Cut it down? Ive helped a few buddies who wouldnt go down the NFA route to put together pistols. I havent used a pistol buffer tube yet that required anything other than a GI carrier, GI spring and GI buffer. The pistol buffer tubes that KAK is putting out even have a shoulder on them for the Sig brace which is pretty slick.
I guess there are a few really short ones out like sinlessorrow posted, but I think those are rare. Those look like it would be used in that PDW stock that the canadians are making similar to the honey badger stock.
It might be easier to chop it off and add a tail piece like the Colt SCW in the photo above than to turn down the OD. I think he may have a Bushmaster carrier that he’s going to let me hack on. If the project goes anywhere, I’ll add an update.
ETA: Does anyone know if the NEA carrier has any buffers in the rear or just the plastic tip?
I’ve milled carriers before for various purposes…they’ve eaten cobalt TiN and TiCN coated end mills. On the whole, I agree with Markm; not worth it with the nonsense pics he provided you. Anyone serious will accept advise to go NFA. Just mY opinion though.
Quick update - I received a Brownells M16 bolt carrier (don’t know who makes them for Brownells) and turned down a portion of the rear, leaving a shoulder for the buffer spring to seat against. It looks similar to the NEA bolt in the photo without the plastic tip. I decided to try turning it first because that still left the option of chopping if off if I totally FUBAR’d it. While it was pretty hard, a good coated carbide insert handled it. The bigger problem was the slot that runs lengthwise down the bolt. This gave an interrupted cut that busted the tip off my insert twice.
Taking light cuts (about .010 to .015) I was able to whittle it down and keep the cutter intact with a good surface finish and gave it back to my customer. If I had to do a bunch of them, I’m sure there is a tougher carbide insert that could handle the interrupted cut that would be better suited for the job. All in all, it was a fun challenge.
I asked my customer to keep me updated on his testing.
Dave, can you expand on this a little? I’m not even sure what the owner is trying to accomplish. Is he trying to replicate a part to work with that stock and receiver extension or is he trying to redesign the carrier / buffer?
I’m very curious. Is he going to be using a stronger spring being that he is eliminating the buffer assembly and reducing the mass of the carrier? The gas pressure at the port is going to be very high and he will definitely need to account for that [now missing] weight somehow.
The project belongs to a customer. I was asked to do the machine work on the bolt carrier and I offered a few suggestions to him but I’m not building the gun.
My concern would be that if something goes kablooey, some bottom feeding attorney is going to be chasing after anyone who had anything to do with this “experiment”. I know, I hate all the liability crap too, but sometimes I think it’s best to be a spectator. The cons seem to outweigh the pros on this job.
I realize the work has already been completed, but for those that stumble across this in the future:
The carrier is typically made from 8620, is heat treated and carburized. There are areas which receive hard chrome, the rest is phosphate after heat treat. The core hardness equates to around RHC 35 if I remember correctly. Tough material, but once you get through the .020" or so of case, it should machine readily.
Yes, I would say that my experience with this carrier matched your description. The interrupted cut was a bigger challenge than cutting though the hard, carburized layer.
