Turk Mauser is an intermediate Mauser action so it's limited to the spacing of these action...1909 Peruvian, 1935 Argentine, commercial Oberndorf and customs such as those by Duane Weibe. The extension in part is a lip to support the rear handguard. This feature is generally machine off for a sporter action. It will leave a receiver that is longer than a large ring Mauser. Since these are small ring thread I believe they can be turned down to "early Rigby" profile. Anybody done this? The high clip bridge is another great feature...short be able to rework to just about any caliber you want for stripper clip feed. Workmanship is excellent....make a great retro sporter. Ron