Now that we have the barrel turned to the correct specs we need to focus on the "barrel extension" part of the build and mill it so it will work in combination with the M261 bolt conversion. We will need to make four cuts (5 if you are using a blank barrel) the first cut will be at the top dead center, this is made to clear the charging handle as the extension goes further into the receiver. The second cut is made on the bottom to clear the magazine you just need to cut away enough to offer proper clearance. The next two cuts are made using a woodruff cutter. Luckily I had the two sizes I needed already on hand so for once I didn't need to buy tooling for a project! The right side of the extension gets a 1/8" slot milled for the extractor and the same for the left side for the wire that helps retain the case (this cut may need hand finished with a round file so the wire does its job). The left side is then cut again for the bolt guide rod. You must measure this cut correctly or the bolt will not seat in and cant possibly causing undue stress and twisting on the whole unit. I will get more detailed pictures up of each cut. This was the prototype so its not really pretty.
|Top has been milled off, slot for extractor is milled (note new garage walls being put up)|
|View of extractor slot, over sized a little but it will work.|
|Left guide rod slot being milled|