Concentricity Tools

I just found a tool on Amazon by RCBS which is set up exactly like yours. I'd trust that form over what I ended up with by hornady, as you can measure more than just the bow or bend in a cartridge. It looks like a very simple tool to make, and will probably be one of the next tools I do build. Thanks for ALL the input! There is great info on this thread!

joe
 
lordbeezer said:
Don’t ask me about my 30 half pint I made up to have a 30 cal ar15 round. (Before the 300 series rounds)
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If that 30 half pint is what I think it is, I would really like to hear about it.
I made up a 30 Fireball in a bolt gun (very close to a 300 Blackout) just for the pleasure of it. The reamer was modified by PTG to my specs so it would shoot the lightest .308 bullets as fast as possible from a 223 case. It was just an exercise to satisfy my curiousity.
 
I’m sure you’ll make a nice one. Reason I didn’t use two bearings at each end didn’t want to add the clearances of bearings into the mix. I’ll be watching for yours.
 
Started off cutting 308 shorter. Reforming to 1.460 to fit ar15 mag. Then inside ream. Shorting 22-250 was the ticket. Less work. Rebarreled nef single shot. Worked up loads. Then reworked 98 Mauser for stronger test bed. Even fed short rounds. Ended up with 110 berger hp and 147 ball. Almost a 1.5x308. Have to pick up a 7.62x39 bolt. Rework a 30 cal barrel and see how it works out. Been on back burner for 11-12 years. 0817769B-6C4E-4217-8D9A-91AF13A5C989.jpeg
 
I finally sat down at the drawing board and threw together a quick plan. Please pardon the lettering - I'm not used to doing that while kneeling at an angle to the board. Anyway, the proof is in the pudding, so I'm going to make this implementation. I'm still waiting on the bearings (623zz bearings ordered back in November, turned out to be from China, expected delivery is February). I think this is slightly overkill, but the structure was to make sure that external variables will be minimized. If desired, one could weld this together without a mill and it should work just fine. Or mill and screw it together without welding. The only machine tool required for this design is a lathe to put a boss on the cartridge rollers. If you offset those frame sides enough, it could easily be done to use larger bearings where you wouldn't need a lathe, but I have one, so I designed it to be done with one.
 

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  • reloading-concentricity_tool.pdf
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I may do a revision, because I am taking issue with the limitations. Right now it is designed for a cartridge with a maximum of 4". I think maintaining size but trimming the sides down a little would get over that, but I am also thinking that larger rollers would help (and trim the top just little on one end) to give it a bigger capacity.

joe
 
Just wondering what makes a cartridge crooked to start with?
Does straightening a cartridge affect neck tension in that cartridge?
 
Tozguy said:
Just wondering what makes a cartridge crooked to start with?
Does straightening a cartridge affect neck tension in that cartridge?
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I believe you are correct. It would decrease the neck's grab in some areas, making it inconsistent. Another side effect would be that
the pressure of changing instead of removing the bullet and re-seating could lower the life expectancy of the case. But, if you only load once (like some do) for long range competitions, it might be a viable option to straighten.
 
That fixture is meant to "check and correct" small amounts of error. By small, I mean a thou or so. I have used that fixture for 10 or 12 years and when I found a round that was out more than that, I went looking for the source of the issue. Sometimes it is something very simple like dirt on one side of the cone of the seating stem. (Wilson seater) Another time it was wear in the press. We reload at the range. It is a dirty environment that causes all kinds of wear on everything that moves. We strive for precision and that means close tolerances. Close tolerances and dirt are not compatible. In the 20 or so years that I have shot benchrest, I think I have gone thru 5 or more presses, many seaters, and over a dozen sizing dies. (made with Newlon blanks - not hardened) The bottom line here is that checking loaded rounds helps validate your loading regimen.
 
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