Sika,
What are you hoping to accomplish by this? We do offer 243 cases and you should be able to find these without too much difficulty. There's a distinct possibility of misfires in this case if it's reformed to 243 and used with slow burning powders, used in colder temps, etc.. We're very specific in warning about this, and recommend that these cases be used for their intended purpose (LR shooting, such as the Palma course). If you do choose to reform the cases, remember to change out your decapping pin. The Palma case uses a 1.5mm (.060") flash hole instead of the normal 2.0mm (.080") pin, and will stick if used with the larger pin.
