Hey guys,
I am looking into doing some neck turning for my 22-250 to try to tighten up the groups even a little more and had the question of what is the best value for product to do this? I've looked at a few tools and they seem to be at around the $50 mark. Is that to be expected and is there any to stay away from? Thanks for the help and knowledge
Here's some thoughts on neck turning. This was to a guy who requested info on neck turning with a hardinge tool room lathe You'll probably end up with more questions than answers but it may offer some pointers as well.
Enjoy.
I’m going to write this on the preface that there is some experience with machining equipment operation and terminology. Things like running tools on center, how tight to pinch a 5C collet, etc. Some things may be a little too specific and if I sound “preachy” I apologize. I don’t want to leave something out so please be patient with me on this part. Initially I just used a 5C collet that would support a majority of the case and then went for it. This worked, but it's not the "right" way to do it as it forces you to take a whole lot for granted. I then modified the process a little and started supporting the case at the web and used a mandrel supported by a drill chuck for the neck.
Think of it as turning between centers. This works fine if you are really careful but I didn't like it all that much because to get a good finish this way the mandrel has to be close to the neck ID and this creates its own set of problems. So, this is my latest idea. Haven't tried it out yet, but I'm pretty sure it’s going to be the hot ticket for this. It’s also the most involved to get going as it requires fabrication of some tooling.I have to assume your set up with 5C collets if you’re using a Hardinge. Step one is to make a die of the same cartridge, preferably with the same reamer that chambered the gun. We’ll use a 6mmBR as an example. Drill/ream a hole in a piece of stock that will support the pilot of the reamer. I suggest using a chunk of 6mm barrel if you have one as the hole and pilot diameter are already done for you. I like tools that have some “meat” to them so I’d use the cylinder portion of the barrel if it were mine.
Run it between centers prior to reaming to get the OD and the bore concentric with one another. Take off just enough to get it cleaned up cause there will be some more work done to the outside after chambering. “Cram” your reamer in there and allow it to go to a depth where just the rim of the case is poking out the back unsupported. A precise depth isn't important. All we are doing is making a tool to support the case body. Now face off the front so that the entire neck of the case is unsupported and hanging out in space. Leave a portion of the shoulder in tact so the case can register off of something. This will aid in setting up your machine for travel stops, etc.
After reaming my next step would be adding a registrable surface on this “die” to datum off of. I’d just turn down the die and leave a flange on the side opposite of the case rim. This way it’ll just purchase up against the face of the 5C collet and you can pop it in and out on the fly. Saves having to mess with a collet stop and I think it’ll give just as good a result. Make sure you undercut at the body/shoulder junction so that the tool radius doesn’t create a fillet. This will mess with your 5C collet when it pulls tight. Again, I’d probably do all this between centers to mitigate TIR between the ID/OD of the part. I assume you see where this is headed.
Next phase would be working on how to retain the cartridge case when it’s in the part. We don’t want it walking out the back and rattling around inside the collet tube/spindle. More than likely there's enough ambient surface friction/tension between the case and the die so that nothing else is needed to hold the case still. (It is only neck turning after all) At this point I’d not modify the collet any and just try it out and see if it works. If it does, then just get to making chips! If it doesn’t then we’ll need to put some cuts in the sides so it’ll squish down when the 5C collet locks up. We are basically making a collet within a collet so I’ll quit calling it a die at this point. I'd then use a super skinny slitting saw , probably a 1/32 and cut three slots on a 120* index. If you have access to an EDM then maybe just cut 4 with that. Don't go the full length of the die otherwise you'll be fiddling with three pieces. Just run it up fairly close to the flange so it keeps itself together.
It needs to deform a tiny amount to bite this case so that you can machine the necks. Couple tricks here to ponder while making this: HSS chamber reamers really respond well to a high sulfur content cutting oil. Mobile Vactra works well and that super stinky crap brownells sells also does. A pipe cutting/threading oil isn’t a bad choice either. Run your reamer no more than 400rpm when chambering this die. It's going to load up with chips fairly quickly so remove and evacuate them often. When you’re done hopefully you don't have "rings of Saturn" in your chamber, but if you do it's still not a big deal cause this is just a collet. "Hone" your chamber with some 220 grit soaked in WD40 and then stop. Don't polish it. We want this thing to "bite" the case so it doesn't move. The finish should resemble a cylinder bore on an engine.
Neck actual turning process: (finally!)
Now, the idea here is that if a guy wants to be SUPER ANAL about neck turning the only way to really really know if the case is going to put that bullet on bore centerline is to machine the OD and ID of the neck concentric with the OD of the case body. In the past, the best luck I’ve had with boring small diameter holes is with a .1875” two flute carbide end mill. Set it up as a boring bar with just one "ear" sticking out to cut with. If you want it really, really nice use a diamond lap and put a radius on the cutting surface. If you haven’t done it this way, your in for a treat as it works pretty dern good. Just have to eyeball the tool to center a bit. You can adjust the relief of the tool just by rotating. Now, take off the absolute bare minimum to clean it up. Right now red lights and sirens should be going off in your head. If you bore the neck, the bullet runs the risk of just slipping in without being retained by anything. Especially if you turn the necks down to the finish diameter. Your right and we’ll address this now.
Lets say your running this 6mmBR in a .262”ND chamber. The bullet measures .2428”. This leaves us a window of .019” to work with. Divide that by two and we don’t even have .01” so you’ll have to be Jonny on the spot with your boring procedure otherwise you’re going to ruin cases. We have to put a bit of extra material on the ID side of this so that you have material removal the whole length of the neck when boring. To do this I’d just size the case with a smaller neck bushing than what you would normally use. Just reduce it a couple thousandths and you should be fine.
Now we can start turning necks on the cases. Like I said, I've never actually done it this way, but it seems (in my head) the way to go so that you truly have a case that is going to put that bullet on bore CL. Here's why I think its the better solution. When you cram a mandrel in a case neck you’re running on the assumption that the neck is concentric to the bore. You’re also assuming that the neck is straight. It is when you have the mandrel in there, but what happens when you remove it? If stuff is kinked or out of whack it’s going to spring right back to how it was before. I can't help but feel that this collet/boring/turning process takes care of all these potential issues because you are machining on the case with a single point tool with the neck in an unsupported/free state. You could just run a custom chucking reamer in the neck and called it good but the reamer would just follow the existing hole.
Now, I make no claims that this is the end all answer, it may turn into a royal PIA that is just too much trouble to bother with. I think done right though it could yield some good results and with a machine like a Hardinge it’s not a difficult or labor intensive process. I say do ten cases this way, then ten cases with a regular neck turning tool and go shoot some groups. That is the end all proof right there, what it does on paper. If you don't see a thing then I'd just use whatever method works the fastest, probably the 5C collet holding the cartridge and then using a hand neck turning tool.
Last thing: Get the radius right on your turning tool so that it's a natural blend into the shoulder. Nothing screams amateur night more than a fat ol bump in the neck/shoulder junction after neck turning. I would think that you’d be able to use a travel stop/dial/DRO to set a limit, but that’s assuming the cases are consistent. There’s a lot of variables here.
Hope this made sense and helps you out. Feel free to give me a call if you want though. 703.673.4251 rings right to my desk.
Cheers and all the best,
Chad