Introduced in 1964, Ruger's 10/22 autoloading rifle is one of the most popular members of the rimfire genre ever. No greater compliment is paid these well-engineered guns than the cottage industries that spring up yearly making accessories and performance parts. Despite all the available upgrades-in-a-box, some of us like doing our own work. The 10/22 is amenable to many simple do-it-yourself modifications.
My sporter model was reasonably accurate but not spectacular. Rather than purchase a new barrel, I elected to see if improved accuracy would be obtained simply from better chamber throat specifications and better headspacing. Many others have written well, and in great detail, before about such modifications but they bear repeating here.
Most .22 target arms are chambered with dedicated match-spec reamers, with shorter chamber body and throat sections than the standard "sporting" chambers. While more finicky about ammo and function, the match chambers center cartridges and minimizes bullet jump to the rifling, thereby improving relative accuracy. My reamer is of the popular "Bentz" pattern and came from Manson Precision Reamers. The body section is about. 100" shorter than the standard chambers.
The first order of business was to tear down the gun and remove the barrel. I'll leave it the readers to study up on this procedure and will recommend the J.B. Woods disassembly guides. On the 10/22, the unthreaded barrel is retained in the receiver by a simple dovetail-clamp arrangement and comes right off.
The machine work for this project is very simple and, if you do not have a lathe, any friendly machine shop could do the work in just a few minutes. Everything else is easily done by hand. All you have to do is face back the barrel shoulder at the receiver shank and shorten the breech face the corresponding amount. .070" to .080" is about as much as you can remove without adding a shim to the dovetail-clamping surfaces. In hopes of maximizing benefits of the improved match-grade throat, I removed around .150" and made a simple shim to take up the slack.
Finishing the chamber can be done by hand if you are careful, since little material is coming out. Cut slowly without lateral pressure and be sure to clear the chips every few thousandths. Whatever you do, do not run the reamer backwards or else you will surely damage it. Just black the breech face of the barrel with magic marker to indicate the...