Product Description
16" barrel for Semi Auto KP31.
Works with slant pattern KP31 shroud. Will work with compensated shroud if the exit hole is opened to .635".
HEADSPACE on Closed Bolt Semi Auto Guns vs Open Bolt / Fixed Firing Pin Blow Back Machine Guns
For the full auto open-bolt original machine gun, the case exposed on rear: .105" - .125". Original KP31 bolts have a bolt face pocket depth of .09". Since these SMGs (as well as the Stemple / BRP SMGs) are fixed firing pin / blow back machine guns, the bolt stops on the back of the case rather than the rear of the barrel. The final critical stage of Open Bolt / Fixed Firing Pin Blow Back SMG process is when the mouth of the case makes a firm and crisp stop on the inside cutout of the chamber. At this instant, the extractor snaps over the case rim and allows the firing pin to contact the primer and detonate the cartridge.
In a closed-bolt semi auto KP31, the chamber depth should be deepened to match the pocket depth in the bolt. Otherwise, the case mouth can get deformed when chambered resulting in massive blow outs at the chamber end. Most semi auto KP31s use modified original KP31 bolts with a bolt face pocket depth of .09". The chamber should be deepened so the case exposed on the rear is just a few thousandths less than the pocket depth on the bolt face. This way the bolt would actually be stopping its forward movement on the back of the barrel rather than on the back of the case. Always inspect and measure these relationships when substituting bolts and barrels in your gun to ensure proper and safe function.
End is threaded 1/2-28
US Made
4140 Alloy Steel
Parkerized Metal Finish
Twist Rate: 1:10
Extractor Location
The extractor relief on this barrel is setup for the BRP-Stemple extractors as well as the original KP31 extractor.
