Case Wobble

[MVW]

I have noticed when turning cases in a chuck, such as an rechargable screwdriver, that the cases wobbles a lot. I note this in the context of turning case necks. Given that there is some play in the mandrel of the neck cutter, it seems like this would degrade the uniformity of the turned necks. Does anyone ever try and square up the cases so that they turn straight?

It also occurred to me that we talk about truing the bolt face on the rifle, but that seems minor compared to the amount of wobble that is inherent in the cases themselves. Does this have any impact on the quality of the cartridges?

I am using a Lee case holder.

Thanks, Mike

 

[jsn]

My guess is the Lee case holder. I was using the Lee case trimming system for small lots of brass rather than adjust the trimmer every time I changed calibers. Every piece of brass that I spun in the case holder in a drill exhibited obvious runout/wobble. Good idea, poor implementation. The result was the trim length at the case mouth was out .002 from side to side. The case holder that goes into the drill is the problem, and the chuck probably doesn't help either.

On the case holder, nothing is square or concentric with anything. The surface the case head rests on is not square to the threads. The hex faces are twisted, not straight. Three case holders, same result.

I contacted Lee to discuss, whoever I spoke to was not impressive. I told him what I had found regarding all of the above, his answer was "we aren't selling these things for very much." After what could best be described as a long pregnant pause, I asked if .002 in case trim length variance on the same piece of brass caused by the case holder was an acceptable tolerance to Lee. The reply was yes. There wasn't any point in discussing anything else.

You're using the Lee case holder, I suspect that is the problem. The chuck on the rechargeable screwdriver probably contributes somewhat to the wobble you describe as well.

But what is the result you're getting in case necks? Do you measure the results to see if the neck thickness is what you want and is uniform?

 

[BoydAllen]

There are several good holders on the market. I would try something else. Sinclair, K&M, and 21st Century Shooting come to mind. Time for a new toy.

 

[Longshooter70]

I noticed the same thing as you. What I did was to take my Lee case holder apart and stoned the surface that the case head presses up against completely flat and true. I then stoned the back of the case holder, the part that screws down, completely flat. On the tip that goes into your drill, there are six sides. I stoned all six completely flat and true as well as the back of the holder. When I chuck it in my drill, I use my hand to tighten the chuck so that it tightens completely flat against the drill chuck. I then make sure when I run the drill it has no apparent wobble. When I put a case into the holder, I make sure the back of the case is flat against the case holder and rotate the case as I tighten it. Give the drill a spin and make sure it runs true, if not, loosen it up and square the case in there.

It sounds more complicated than it is. It only takes a half hour or so and it eliminates a whole lot of run out. I hold the neck trimmer in my hand so any runout is felt, plus it's not a rigid mount that may cause the case neck to deform.

May sound crazy but it works for me as I have very little neck runout due to neck turning. YMMV...

John

 

[wapiti25]

You should have a mandrel that fits snug in your brass. Tight enough to require a good lube such as STP and oil mixed, the cases need to be tight to cut true. You should measure the case neck thickness with a ball mic at least 4 places around the neck and see how the thickness varies after turning. Casenecks can be cocked or "wobble" because of the sizing dies used. You need to check cases as they come out of your rifle and make certain that they are good from the chamber. You are on the right track with your question, make sure where the run out is coming from.

 

[MVW]

Thanks for the suggestions. I am using a K&M expander mandrel and neck turning tool, so the case fits pretty tight over the pilot. However, it seems like the neck thickness uniformity isn't all that improved. On some cases, if I move the case a bit in the holder it will have less runout, so I suspected that it had more to do with the cases, but I may try a different a different case holder and see how that works.

 

[tenring]

Get the Sinclair case holder, and really tighten it down. You should have just a tad of wobble, and that is OK>

 

[Leaddog]

21st Century with lathe eliminates your problems.

 

[Wooly]

There are several good holders on the market. I would try something else. Sinclair, K&M, and 21st Century Shooting come to mind. Time for a new toy.

Found this old post from an internet search. Hopefully some of you are still subscribed.

I am having the same problem and have been ever since I started turning necks a few years back. I own and use all three of the systems that Boyd list above. I get the case wobble in all three. The brass I use is Lapua and Federal Premium. So, I think the majority of the wobble is coming from the brass and not the chuck since they all do it.

I'm in the middle of working up 200 pieces of "once fired" Federal Premium 308 that was given to me by a buddy. It came from a police department. Here are my steps, in order, so far:

- Tumbled clean.
- FL sized through a Forster Comp die and CoAxial press.
- They were still a little snug in my chamber so I bumped the necks back as far as I could using a Redding Comp Body Bump die and a Big Boss II press. Now they chamber with minimal effort. The cops must have had loose chambers.
- Expanded the necks using a KM expander mandrel.
- Turning the necks using the hand held KM Neck Turner, KM Turning Mandrel and powering the chuck with a drill.
- I see lot of wobble. Some worse than others.

Here is what I know: The case necks are of uniform thickness after turning. They measure with variations less than 4 ten/thou (.0004). I think that is good and a big improvement over factory.

Could the shell holders and collets be made more precisely? No doubt. But I think that the majority of this wobble is coming from the cases themselves. When put on a Sinclair concentricity gauge or a Neco, the cases show runout between the neck and the body. Some in access of 4 thou. Not good at all. This even after these cases have been sized twice through precision equipment.

I think it was David Tubb on one of his old videos that talked about the "banana" in a fired case. This due to the microscopic variation in brass thickness that does not let the brass return to its original shape after firing or when originally produced. Anyway he marked each loaded round with a Sharpie at the apex of it's runout and oriented the mark at 12:00 o'clock when chambering the round for firing. I guess he also culled some of the worse cases. He said it improved his groups significantly. Maybe things like that were why guys like him won so many national championships?

I will check again for concentricity of the bullet to the case body once these are loaded. I bet there will be some variations even though the neck thickness is very uniform. This is an aggravating deal and I am not sure of was causes it all or the best way to deal with it.

Cheers,
Woolly

 

[BoydAllen]

I think that you need to upgrade your case holder. Recently I got a 21st Century holder that I think very highly of. If you let the case and turner wobble, and go to the shoulder much too fast to make a clean cut, and return to the mouth slowly, your necks should be very uniform. Are you turning necks that have been expanded up quite a bit, or are they the same caliber as the case was made?

 

[Wooly]

I think that you need to upgrade your case holder. Recently I got a 21st Century holder that I think very highly of. If you let the case and turner wobble, and go to the shoulder much too fast to make a clean cut, and return to the mouth slowly, your necks should be very uniform. Are you turning necks that have been expanded up quite a bit, or are they the same caliber as the case was made?

Yes, I have the whole 21st Century setup. I can turn the case necks to a uniform thickness of .0004". But the cases are still not concentric.

 

[BoydAllen]

No turner will make a case straighter. That's not what they are intended for. If they do a good job of making your necks' thickness uniform, you have the best that you can expect. For straighter you need to look at your FL sizing. For hard brass, annealing may help them straighten better from being fired.