I made one for my 45/70 Guide Gun from one of the NTN plastic bore guides for a bolt action. Pull out the yellow pastic end and cut off the small cylindrical section from the other end. I did this quite a while ago so I'm going from memory here. I think I cut away a little of the bevel also to get closer to the inside diameter. Then I put a sharp 1/2" drill in the drill press and started to drill/ream from the beveled end to enlarge the guide from that end. The hole down the center of the guide is tapered and did not require enlarging from the end where the yellow plug was. Careful, the plastic guide is hard to hold in the drill press, so I held on to it by hand. Hold on tight, it wants to twist out of your hands. The hole down the middle now ends up slightly smaller than 1/2" because the plastic seems to stretch over the drill as you try to enlarge the hole. You will end up with a small bevel remaining at the end of the guide, just enough to seal against the chamber openning. Works great. Oh yes, you also have to cut off the plastic handle that sticks out the side of the guide. Hope this helps, Hart.
Whoops, after rereading your post I see its for a bolt action and not a lever action. Just leave the the handle on, the one that fits where the bolt handle goes.
i did the same thing as hart-- took a standard MTM guide, removed the yellow part, cut the tapered part off closer and used a standard case de-burring tool (or a uni-bit, if ya got one) to enlarge the hole to the proper size.
