I'm looking at getting a reamer for one of their calibers made and was wondering who makes the reamers for them. Thanks

I would not be the least surprised that they make their own. You can get clones from various places, but the JDJ's are guarded proprietary cartridges. Call him and he'll tell you. You want a JDJ, Mr. Jones will do the work.

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"Use A Big Enough Gun!"

You can get a custom reamer of the same dimensions as a JDJ cartridge, but just don't call it a JDJ.