Anybody with access to machine tools can aim a hole down the middle of a bolt. Without machine tools it would be difficult.

I wonder what the diameter of the reamer is. Given the cost of the tool, I'd say making a homemade reamer is worth pursuing. Like biopete mentioned, why not use a drill bit?

I wouldn't obsess over any carbon that stays in the chamber. The material is soft and not abrasive, so it can't harm the surfaces as metal or dirt can.

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95 E320 Cabriolet, 169K