What is involved in chambering a Marlin 336 to 30-30 AI? Can it be done without removing the barrel or does it need to be set back a turn? I just picked up a used Marlin and would like to make it my first wildcat. DW

No bbl set back is necessary if the current headspace in the rifle is good.
Both headspace on the case rim.
The A/I version extends and straightens out the shoulder to give some more case capacity.

If the reamer extension w/reamer can fit into the disassembled receiver from the back, it can be done by hand.
Many gunsmiths would want to pull the bbl and set it up in the lathe to do the work.

Thanks, in the article I read It was done by hand. I didn't think about headspacing on the rim. DW

But Marlin barrels are so easy to remove there is no reason not to; then you can see what you are doing; assuming you are going to ream it by hand. By lathe is always better.