A while ago I posted a thread asking about installing an AR rifle barrel on a receiver with M4 feed ramps. I thought I 'd post my results just as a matter of information. I thought about trying to make a video of it, but have neither the knowledge or equipment to do so, and it's too late now as it's already done. I don't claim any expertise, nor am I trying to knock anyone who tried without success to make it work, or said it couldn't be done. This has worked for me so far. The first thing I did was to search the net for info. General opinion is that you don't fool with the ramps in the receiver itself so you don't cut through the anodizing. I found a video showing how to do it with a Dremel tool, an abrasive stone, two grits of Cratex wheels and polishing compound. Having used a Dremel before I knew they can be hard to control in a close area. I've also learned from experience that any grinding wheel will cut much faster on a surface you don't want to cut than one that you do. I chose a different method. I first tried needle files, but the barrel extension was hard enough to resist filing, so I used a cheap set of diamond coated files that are sold at hardware stores, flea markets, etc. They worked quite well. Step one was to carefully move the bottom of the ramps in the extension forward until they were even with the receiver ramps with no overhang to snag the bullet nose. Next I blackened the ramps with a black felt tip marker. Using the half-round file, I then cut the middle of the ramps down to blend the center area to the top and bottom areas, not taking any material off either end of the ramps. I was also careful not to widen them. I don't think the inner side is too important, but the outer probably is.
After they looked about right, I polished them with a red Cratex wheel, bullet shaped. I also broke the corners at the tops of the bolt lug clearance cuts and lightly polished them so they wouldn't scratch the bullets or cases as they slid by on their way into the chamber.
After re-assembly, I cycled a couple of different types of rounds through the action without firing them. Later I was able. to get to a range and try the rifle out. It cycled flawlessly with Win. 55 gr. FMJ target loads and some old soft point handloads I got in a trade 30 years ago. Two different magazines were used, one steel and one plastic. May be beginner's luck, but it has worked, so far.
After they looked about right, I polished them with a red Cratex wheel, bullet shaped. I also broke the corners at the tops of the bolt lug clearance cuts and lightly polished them so they wouldn't scratch the bullets or cases as they slid by on their way into the chamber.
After re-assembly, I cycled a couple of different types of rounds through the action without firing them. Later I was able. to get to a range and try the rifle out. It cycled flawlessly with Win. 55 gr. FMJ target loads and some old soft point handloads I got in a trade 30 years ago. Two different magazines were used, one steel and one plastic. May be beginner's luck, but it has worked, so far.