Turning down a Lee 308 Collet die mandrel?

[jlow]

Anyone have any experience turning down this die?

I mic the mandrel and a 175gr SMK and I figure the difference is about 2.5 thousands and with the spring back the actual neck tension is probably only based on a 1.5 thousands – good for NRA high power single load but perhaps not for mag loaded rounds especially if I want to keep my OAL relatively consistent.

Was thinking of putting the mandrel on a drill press and turning it down one more thousands to get a total hold of 2.5 thousands using 600 grid sand paper – anyone done this with success?

 

[bozo699]

jlow,
I imagine you could but be very careful to stay as even with pressure and coverage of the sandpaper to keep the mandrel a consistent size as possible.
Wayne.

 

[jlow]

Thanks Wayne - good advice!

 

[bozo699]

jlow,
If it were me doing it and I didn't have a lathe I would do as you are planning, when you get it where you want it, take a accurate measurement of it (with Mic) not calipers and call Lee they sell them in increments of .001 I believe, that way you will have one that is near perfect and a mirror finish, of course then again if you have ever looked inside a Lee die there finish looks like they used a rat tailed file ??? I am having Lee make me a custom collet die for my 6brx and I am purchasing several sized mandrels with it, I hope it works good.
Wayne.

 

[jlow]

Hey guys thanks a lot – I did not realize Lee has that service, will call them up and see what they say.

I do have some concerns as to how even I can take the mandrel down with sandpaper – visions of wiggle worm comes to mind – LOL! Yea, unfortunately I don’t have a lath and so…. I do have a good Mitutoyo digimatic micrometer but if I screw it up, it will be too late.

 

[ReedG]

You actually can do a pretty good job with a drill and extra fine emery cloth. Turn the mandrel at a fairly rapid speed and really just polishing it will take off .001. Be careful to do the full length of the mandrel so as to not get the top part smaller than the lower portion.

 

[jlow]

Thanks Dave for the encouragement and link! As they say, “Great minds think alike” – I have another collet die on the way to me right now as I write.

Being a DIYfer, I will give this a go with my drill press, it has a ½ chuck and so works well. In the mean time, I will also likely order one of those shinny beauties with the mirro finish from Lee now that Wayne has put that image in my head that will not go away – LOL! What will we men do without our tools?

 

[MrMajestic]

Back up your abrasive material with a flat file and it will give you a straighter job.

 

[jlow]

Thanks guys again. Gave it a go today with the one I had. Started off with the diamond file but it was very slow going and so I switched over to a length of 400 grit sandpaper shaped like a band one inch wide and about six inch long, held each end with my two hands and basically moved it up and down moving the band back and forth like a saw but using the flat one inch area flat against the mandrel and it went fast – only took about one minute total time with repeated check along the way with the micrometer. Repeated the sequence with another similar shaped band of 600 grit paper and smooth it out like a mirror.

Here is a photo of the mandrel. You can see that I only sanded from the decapping pin area up about 2/3 of the way. The reason I did not go higher is because it was not necessary. The collet mush down on the case in the area where I put that red bar, this is pretty obvious when you look at the design of the die and also where the brass left an color impression rubbing against the mandrel.

Measured the finish product with the Mitutoyo micromer in four areas starting at the red bar and going all the way to the decapping pin, took three readings around the mandrel at each area and here are the averages: 0.30420”, 0.30430”, 0.30438”, and 0.30443” –so pretty close within 0.0002” variance increasing as you go down towards the decapping pin which was expected. The average of all the numbers is 0.30434” which is 0.00133” smaller than the 0.30567” diameter I started out with.

I next size a case neck which had previously been sized with the thicker mandrel. Took three measurement around the neck, ran it through the new resized mandrel and took another three measurements – neck thickness decreased by 0.00112” so that is very close to the 0.00133” reduction in size of the mandrel and pretty much what I wanted – success!

 

[bozo699]

Good deal jlow, sounds like it is plenty accurate enough to make good ammo, probably as accurate as it was when it came from Lee anyway, a neat project with a positive outcome
Wayne.

 

[jlow]

Thanks Wayne! Will know when I shot that OCW that I made up with it today - LOL!